BEGIN:VCALENDAR PRODID:University of Cologne\, ITP\, Events Server X-WR-TIMEZONE:Europe/Berlin BEGIN:VEVENT SUMMARY:CMT | Oksana Sukhostavets DTSTART;TZID=Europe/Berlin:20140912T140000 DTEND;TZID=Europe/Berlin:20140912T153000 DTSTAMP:20260527T090436Z UID:0000000523@events.thp.uni-koeln.de DESCRIPTION:Oksana Sukhostavets\, University of San Sebastian\n\nLinear an d nonlinear vortex dynamics in single and coupled magnetic discs\n\n\n\n Contact Person: Achim Rosch LOCATION:Seminar Room of the Institute for Theoretical Physics END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Bela Bauer DTSTART;TZID=Europe/Berlin:20140916T140000 DTEND;TZID=Europe/Berlin:20140916T153000 DTSTAMP:20260527T090436Z UID:0000000519@events.thp.uni-koeln.de DESCRIPTION:Bela Bauer\, Microsoft Station Q\n\nArea laws in a many-body l ocalized state and its implications for topological order\n\nThe question whether Anderson insulators can persist to finite-strength interactions - a scenario dubbed many-body localization - has received a great deal of in terest. We formulate a precise sense in which a single energy eigenstate o f a Hamiltonian can be adiabatically connected to a state of a non-interac ting Anderson insulator\, and define a many-body localized phase based on this. We explore the possible consequences of this\; the most striking is an area law for the entanglement entropy of almost all excited states in a many-body localized phase. We present the results of numerical calculatio ns for a one-dimensional system of spinless fermions. Furthermore\, we stu dy the implications that many-body localization may have for topological p hases and identify scenarios in which many-body localization can help to s tabilize topological order at non-zero energy density. We also explore the ways in which a relatively small quantum computer could be leveraged to s tudy many-body localization. We show that\, in addition to studying time-e volution\, a quantum computer can\, in polynomial time\, obtain eigenstate s at arbitrary energies to sufficient accuracy that localization can be ob served.\n\nContact Person: Simon Trebst LOCATION:Seminar Room\, Conainer Building END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Lukas Janssen DTSTART;TZID=Europe/Berlin:20140917T100000 DTEND;TZID=Europe/Berlin:20140917T113000 DTSTAMP:20260527T090436Z UID:0000000525@events.thp.uni-koeln.de DESCRIPTION:Lukas Janssen\, Simon Fraser University\n\nQuadratic band touc hing points in 3D: NFL phase versus topological Mott instability\n\n\n\nCo ntact Person: Achim Rosch LOCATION:Seminar room of the Institute for Theoretical Physics END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Lih-King Lim DTSTART;TZID=Europe/Berlin:20140925T140000 DTEND;TZID=Europe/Berlin:20140925T153000 DTSTAMP:20260527T090436Z UID:0000000524@events.thp.uni-koeln.de DESCRIPTION:Lih-King Lim\, Institut d'Optique\, Palaiseau\n\nDirac cones m erging transition and geometric phase in Stuckelberg interferometer with c old atoms\n\n\n\nContact Person: Achim Rosch LOCATION:Seminar Room of the Container Building END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Wolfgang Lechner DTSTART;TZID=Europe/Berlin:20140930T100000 DTEND;TZID=Europe/Berlin:20140930T113000 DTSTAMP:20260527T090436Z UID:0000000513@events.thp.uni-koeln.de DESCRIPTION:Wolfgang Lechner\, University of Innsbruck\n\nQuantum Soft Mat ter with Cold Polar Molecules: Glass and the Hexatic Phase\n\nThe realizat ion of cold ensembles of polar molecules has opened a new pathway to explo re the dynamics of quantum many body systems with strong\, long-range and anisotropic dipolar interactions. While theoretical studies have so far fo cused on the equilibrium phases in the highly degenerate quantum regime \, I will focus in my talk on non-equilibirum dynamics in the regime where q uantum and thermal fluctuations are of the same order of magnitude. I will present two proposals: i.) a study on the glass transition in the presenc e of quantum fluctuations and ii.) a study on quantum fluctuations in the hexatic phase. i.) I will show\, how the glass phase can be prepared in a bilayer system of ultracold dipolar molecules and present results on class ical and quantum glassy behavior\, characterized by long tails in the rela xation time and dynamical heterogeneity. I will also present experimental accessible order parameters based on marker molecules\, distinguished by p roperly chosen internal levels\, and find quantum features of dynamical he terogeneity. ii.) The hexatic phase is an intermediate phase in two dimen sional systems when going from the crystal to the liquid phase. I will pre sent results on the influence of quantum fluctuations on the nature of the hexatic phase and methods that allow one to measure these effects in a se tup with polar molecules. \n\n\n\nContact Person: Philipp Strack LOCATION:Seminar Room of the Institute for Theoretical Physics END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Jean-Marie Stephan DTSTART;TZID=Europe/Berlin:20141024T140000 DTEND;TZID=Europe/Berlin:20141024T153000 DTSTAMP:20260527T090436Z UID:0000000515@events.thp.uni-koeln.de DESCRIPTION:Jean-Marie Stephan\n\nEntropy and Mutual information in low-di mensional classical and quantum systems\n\n\nIn studies of quantum phases of matter\, the\nentanglement entropy has established itself as an importa nt practical\nresource. For example it is universal at one-dimensional qua ntum critical\npoints: the leading term can be used to extract the central charge\nc of the underlying conformal field theory\, and thus identify th e\nuniversality class. I will show how an analogous\ninformation theoretic quantity defined for classical systems\, the\nRenyi Mutual Information (R MI)\, can be used to access universality\nclasses in 2d. In particular for a rectangle cut into two rectangles\,\nthe shape\ndependence of the RMI c an be computed exactly and is proportional to c.\n\nI will also discuss ho w this Mutual information is related to the\nentanglement entropy of certa in Resonating valence bond states in\n2d\, as well as other basis-dependen t entropies in 1d quantum\nsystems. In all cases\, the information theoret ic approach\nprovides an efficient way of identifying the various competin g orders\nin a given classical or quantum system.\n\n\nContact Person: Joh annes Helmes LOCATION:Seminar Room of the Institute for Theoretical Physics END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Pablo Serna Martinez DTSTART;TZID=Europe/Berlin:20141031T140000 DTEND;TZID=Europe/Berlin:20141031T153000 DTSTAMP:20260527T090436Z UID:0000000564@events.thp.uni-koeln.de DESCRIPTION:Pablo Serna Martinez\, Universidad de Murcia\n\nDeconfined qua ntum criticality in a 3D classical loop model\n\nLoops arises as long leng th description for many quantum problems\, in particular for SU(n) magnets . An interesting scenario in this kind of problems is the so-called deconf ined criticality\, a transition between Néel and valence bond solid phase s in 2D quantum magnets\, where numerical studies support a continuous pha se transition but also display strong violations of finite size scaling th at are not yet understood. This scenario is also believed to describe the phase transition for classical magnets where hedgehogs are suppressed. Thr ee dimensional completely-packed loop models were shown to describe the sa me features as quantum magnets in 2D and the phase transition between a N éel state and a valence bond liquid. By modifying these loop models we ca n drive them to a phase transition with the same features: a magnetic orde red phase where there are long loops and a paramagnetic phase where a latt ice symmetry is broken. In common with the direct studies of quantum Hamil tonians\, we find strong violations of scaling for the SU(2) case. We desc ribe accurately these violations and reach larger sizes than previous stud ies\, making use of a wide range of observables. However\, we do not find any conventional signs of a first order transition.\n\n\nContact Person: S imon Trebst LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Johannes Reuther DTSTART;TZID=Europe/Berlin:20141114T140000 DTEND;TZID=Europe/Berlin:20141114T153000 DTSTAMP:20260527T090436Z UID:0000000543@events.thp.uni-koeln.de DESCRIPTION:Johannes Reuther\, FU Berlin\n\nA functional renormalization-g roup approach for frustrated quantum spin-systems\n\nWe apply the function al renormalization group (FRG) method to describe\nground state properties of frustrated spin-1/2 systems on two-dimensional\nlattices. In order to be able to use this technique we rewrite the spin\noperators in terms of p seudo fermions. The resulting fermionic model is\nthen treated via FRG\, w hich manages to sum up diagrammatic contributions\nin different interactio n channels in infinite order. Calculating the\nmagnetic spin susceptibilit y we determine the ground state phase diagrams\nof various frustrated spin systems. Thereby\, we discuss models such as the\nJ1-J2 Heisenberg model on the square lattice and the Kagome Heisenberg\nmodel. A specific focus w ill be on the iridate compound Li_2IrO_3\, where\nexperiments suggest a ma gnetically ordered ground state of incommensurate\nspiral type. Applying o ur FRG technique to an extended Heisenberg-Kitaev\nmodel we are able to de velop a microscopic scenario for the exchange\ninteractions in this compou nd\, explaining the experimental findings.\n\n\nContact Person: Simon Treb st LOCATION:Seminar Room 03 - ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Wolf Wuester DTSTART;TZID=Europe/Berlin:20141205T140000 DTEND;TZID=Europe/Berlin:20141205T153000 DTSTAMP:20260527T090436Z UID:0000000574@events.thp.uni-koeln.de DESCRIPTION:Wolf Wuester\, ETH Zuerich\n\nCavity quantum electrodynamics w ith many-body states of a two-dimensional electron gas\n\nLight-matter int eraction has played a central role in understanding as well as engineering new states of matter. Reversible coupling of excitons and photons enabled groundbreaking results in condensation and superfluidity of nonequilibriu m quasiparticles with a photonic component. We investigated such cavity-po laritons in the presence of a high-mobility two-dimensional electron gas\, exhibiting strongly correlated phases. When the cavity was on resonance w ith the Fermi level\, we observed previously unknown many-body physics ass ociated with a dynamical hole-scattering potential. In finite magnetic fie lds\, polaritons show distinct signatures of integer and fractional quantu m Hall ground states. Our results lay the groundwork for probing nonequili brium dynamics of quantum Hall states and exploiting the electron density dependence of polariton splitting so as to obtain ultrastrong optical nonl inearities.\n\nContact Person: Philipp Strack LOCATION:Seminar Room 03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Thomas Lang DTSTART;TZID=Europe/Berlin:20141212T140000 DTEND;TZID=Europe/Berlin:20141212T153000 DTSTAMP:20260527T090436Z UID:0000000548@events.thp.uni-koeln.de DESCRIPTION:Thomas Lang\, Boston University\n\nDimensionless ratios for SU (N) symmetric Hubbard models and their critical points\n\nUsing unbiased q uantum Monte Carlo simulations we investigate the quantum phase transition s in SU(N) Hubbard models on square and honeycomb lattices. We construct a nd measure dimensionless fermionic correlation and order parameter ratios\ , which provide precise and independent estimates for the couplings at whi ch a mass gap opens in the single particle spectrum and at which the order sets in. Furthermore these correlation ratios prove to be highly sensitiv e to weak order and render the need of pinning fields unnecessary. In par ticular\, we study the nature and location of the phase transition between the semi-metal and Mott insulating antiferromagnetic state in the SU(2) H ubbard model on the honeycomb as well as the potentially deconfined Neel t o valence bond solid phase transition in the SU(6) Hubbard model on the sq uare lattice.\n\n\nContact Person: Simon Trebst LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Zala Lenarcic DTSTART;TZID=Europe/Berlin:20150116T140000 DTEND;TZID=Europe/Berlin:20150116T153000 DTSTAMP:20260527T090436Z UID:0000000615@events.thp.uni-koeln.de DESCRIPTION:Zala Lenarcic\n\nNonequilibrium properties of Mott insulators\ n\n\n\nContact Person: Achim Rosch LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Natan Andrei DTSTART;TZID=Europe/Berlin:20150119T140000 DTEND;TZID=Europe/Berlin:20150119T153000 DTSTAMP:20260527T090436Z UID:0000000565@events.thp.uni-koeln.de DESCRIPTION:Natan Andrei\, Rutgers University\n\nQuench dynamics in integr able quantum many body systems\n\n\n\nContact Person: Achim Rosch LOCATION:Seminarraum 0.03 Gebaeude TP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Henry Legg DTSTART;TZID=Europe/Berlin:20150123T140000 DTEND;TZID=Europe/Berlin:20150123T153000 DTSTAMP:20260527T090436Z UID:0000000569@events.thp.uni-koeln.de DESCRIPTION:Henry Legg\, University of St Andrews\n\nApplications of magne tohydrodynamics to condensed matter - A Ward identity for magnetic helicit y\n\n\n\nContact Person: Achim Rosch LOCATION:Seminar Room 03 - ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Christopher Max DTSTART;TZID=Europe/Berlin:20150130T140000 DTEND;TZID=Europe/Berlin:20150130T150000 DTSTAMP:20260527T090436Z UID:0000000633@events.thp.uni-koeln.de DESCRIPTION:Christopher Max\, University of Cologne\n\nQuantum Criticality of Crystals\n\n\n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Andrey Bolotnikov DTSTART;TZID=Europe/Berlin:20150410T140000 DTEND;TZID=Europe/Berlin:20150410T153000 DTSTAMP:20260527T090436Z UID:0000000660@events.thp.uni-koeln.de DESCRIPTION:Andrey Bolotnikov\, Duesseldorf\n\nScattering of electrons in graphene: some of recent results\n\nAfter the experimental realization of graphene by Novoselov and Geim in 2004\, for which they were awarded the N obel Prize to in 2010\, the scattering theory of two-dimensional massless Dirac fermions has become relevant because of its role in understanding gr aphene's transport properties. The latter motivated Jhih-Sheng Wu and Mich ael M. Fogler to study the problem of scattering on a circular step-like p otential barrier\, which is assumed to be a model for a circular cluster o f charged impurities. The aim of the talk is to make an overview of some m ain aspects of their recent article Scattering of two-dimensional massless Dirac electrons by a circular potential barrier [1]. In this publication the scattering problem was treated with respect to the values of two param eters\, X and rho\, characterizing the size and the strength of the barrie r\, respectively. For each combination of X and rho a suitable tool was fo und for studying the scattering problem. One of the article's conclusions is the fact that formation of circular clusters increases the conductivity compared to the case of randomly distributed impurities.\n\n[1] Jhih-Shen g Wu and Michael M. Fogler\, Scattering of two-dimensional massless Dirac electrons by a circular potential barrier\, arXiv: 1410.0272v1 1 Oct 2014. \n\nContact Person: Maria Hermanns LOCATION:Seminar room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Victor Jouffrey DTSTART;TZID=Europe/Berlin:20150415T143000 DTEND;TZID=Europe/Berlin:20150415T160000 DTSTAMP:20260527T090436Z UID:0000000670@events.thp.uni-koeln.de DESCRIPTION:Victor Jouffrey\, University of Lyon\n\nSound absorption in No n-Kramer Quantum Spin Ice\n\nIn this talk\, I will be presenting the conse quence of the coupling between magnetic and vibrational degrees of freedom in Non-Kramer Quantum Spin Ice models focusing on experimentally relevant signatures for this specific class of quantum spin liquid. First\, I will introduce Quantum Spin Ice physics borrowing insights from its well-studi ed classical counterparts. In particular\, our work will build on the assu mption that the monopole excitations present in classical Spin Ice remains well-defined quasi-particles. Quantum fluctuations of the spins provide a coherent mechanism for the transport of monopoles and lead to the emergen ce of a U(1) gauge field and an associated gapless photon. I will briefly explain how the pseudospin living on the vertex of the pyrochlore lattice emerges from the combination of single-ion physics and crystal field symme tries and insist on the importance of its non-Kramer nature to couple line arly phonons. The coupling between magnetic and vibrational degrees of fre edom will be introduce on physical grounds and its form will be inferred f rom simple symmetry arguments. The last part of the talk will be focused o n the consequences of this coupling on sound absorption measurements empha sizing the major role of the gapless photon.\n\nContact Person: Maria Herm anns LOCATION:Seminar room\, Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Yoran Tournois DTSTART;TZID=Europe/Berlin:20150417T140000 DTEND;TZID=Europe/Berlin:20150417T150000 DTSTAMP:20260527T090436Z UID:0000000667@events.thp.uni-koeln.de DESCRIPTION:Yoran Tournois\, Utrecht University\n\nThe holographic electro n star\n\nThe Anti-deSitter/Conformal Field Theory (AdS/CFT) correspondenc e is a duality relating strongly correlated quantum field theories to clas sical gravity in one higher dimension. Although discovered in the context of string theory\, it has more recently been applied to condensed matter p hysics\, where it offers insight into strongly correlated systems at a qua ntum critical point. \n\nIn this talk\, I will briefly introduce the AdS/C FT correspondence and indicate the connection to condensed matter physics. I turn to the electron star\, a model of a perfect fluid of charged fermi ons backreating onto the geometry. I will discuss the numerical results ob tained by solving the resulting equations of motion. Then\, I turn to a de scription of fermions in curved spacetime\, after which I will consider th e fermion equations of motion in the electron star background. Finally\, a s an outlook\, I will mention several extensions of this model.\n\nContact Person: Maria Hermanns LOCATION:TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Lei Wang DTSTART;TZID=Europe/Berlin:20150424T140000 DTEND;TZID=Europe/Berlin:20150424T153000 DTSTAMP:20260527T090436Z UID:0000000655@events.thp.uni-koeln.de DESCRIPTION:Lei Wang\, ETH Zurich\n\nRecent Surprises in the Simulation of Quantum Phase Transitions\n\nI will talk about two recent surprises in th e quantum Monte Carlo (QMC) simulation of quantum phase transitions. \n\nS urprise one is the solution of a thirty years old sign problem by Huffman and Chandrasekharan. It enables us to study the fermionic quantum critical point of spinless Dirac fermions using unbiased continuous-time QMC simul ations. Compatible results are also obtained from infinite projected entan gled-pair states calculations. I will compare the numerical results with p redictions of the Gross-Neveu theory and discuss their physical implicatio ns. \n\nSurprise two is a generic\, efficient and elegant approach to comp ute fidelity susceptibility of correlated fermions\, bosons\, and quantum spin systems in modern QMC methods. It can be used to detect quantum phase transitions without any prior knowledge of the local order parameter. Usi ng it I will shed light on the hypothetical spin-liquid phase in the Hubba rd model on honeycomb lattice. \n\n\nContact Person: Simon Trebst LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Johannes Knolle DTSTART;TZID=Europe/Berlin:20150508T140000 DTEND;TZID=Europe/Berlin:20150508T153000 DTSTAMP:20260527T090436Z UID:0000000656@events.thp.uni-koeln.de DESCRIPTION:Johannes Knolle\, Cambridge\n\nDynamics of a Quantum Spin Liqu id\n\nTopological states of matter present a wide variety of striking new phenomena\, most prominently is the fractionalization of electrons. Their detection\, however\, is fundamentally complicated by the lack of any loca l order. While there are now several instances of candidate topological sp in liquids\, their identification remains challenging. Here\, we address o ne of the key questions: How can a quantum spin liquid phase be diagnosed in experiments?\nWe find that the dynamical response can serve as a valuab le tool for diagnosing quantum spin liquids. We provide a complete and rar ely available exact theoretical study of the dynamical structure factor an d the inelastic Raman scattering response of a two-dimensional quantum spi n liquid in Abelian and non-Abelian phases. We show that there are salient signatures of the Majorana fermions and gauge fluxes emerging in Kitaev's honeycomb model. Our analysis identifies new varieties of the venerable X -ray edge problem and explores connections to the physics of quantum quenc hes.\nA number of proposals suggest that some materials with strong spin-o rbit coupling\, e.g. {Na/Li}2IrO3 or alpha-RuCl3 compounds\, realize some of the physics of the Kitaev model. We discuss the current experimental si tuation\, recent measurements and explore more generally the effect of bre aking the integrability on response functions of Kitaev spin liquids. \n\n Contact Person: Maria Hermanns LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Olga Petrova DTSTART;TZID=Europe/Berlin:20150522T140000 DTEND;TZID=Europe/Berlin:20150522T153000 DTSTAMP:20260527T090436Z UID:0000000657@events.thp.uni-koeln.de DESCRIPTION:Olga Petrova\, MPI-PKS\n\nDefects and Majorana modes in the Ki taev honeycomb model\n\nKitaev's honeycomb model [1] is a quantum spin liq uid\, celebrated for\nboth the richness of its physical features\, and the fact that it\nadmits an exact solution. The latter can be cast in terms o f Majorana\nfermions living in the background of a static Z_2 gauge field. The\ngapped phase of this model exhibits Z_2 topological order\, equivale nt\nto that of the toric code. Its ground state is a featureless spin\nliq uid whose nontrivial properties can be revealed by introducing\nlattice de fects. In the talk I will show that certain kinds of lattice\ndislocations and bond defects in this originally Abelian system carry\nunpaired Majora na fermions [2\,3]. Each pair of such defects gives rise\nto a non-local p hysical fermion mode\, i.e. a topologically-protected\nqubit\, made out of two Majorana modes connected by a Z_2 gauge string.\nThe qubit's composit ion reveals the crucial role of the emergent gauge\nfield\, neglected in m ost treatments of the Kitaev model\, in the\nphysics of Majorana modes. I will demonstrate how the non-local\nfermion can be created or annihilated by winding a magnetic vortex\naround a defect.\n\n[1] A. Kitaev\, Ann. Phy s. 321\, 2 (2006).\n[2] O. Petrova\, P. Mellado\, O. Tchernyshyov\, Phys. Rev. B 88\, 140405 (2013).\n[3] O. Petrova\, P. Mellado\, O. Tchernyshyov\ , Phys. Rev. B 90\, 134404 (2014).\n\nContact Person: Maria Hermanns LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Stefan Maier DTSTART;TZID=Europe/Berlin:20150529T140000 DTEND;TZID=Europe/Berlin:20150529T153000 DTSTAMP:20260527T090436Z UID:0000000685@events.thp.uni-koeln.de DESCRIPTION:Stefan Maier\, University of Cologne\n\nThe quest for the anti ferromagnetic strange metal: ideas for the Wilsonian renormalization group \n\nWhile the problem of calculating critical exponents was believed to be \nessentially solved by some experts already in the 1980s\, this does not\ nhold true for metallic systems at present. In a recent study of the\nspin -fermion model [1]\, Sur and Lee have found the first renormalization\ngro up fixed point for a quantum-critical metal using an\nepsilon-expansion ar ound $d=3$. The critical theory was shown to have a\nquasi-local boson and one-dimensional electrons. However\, the nature of\npotential fixed point s in the physical dimensionality $d=2$ and the\nvalues of critical exponen ts are an important open problem. In this\ntalk\, I will therefore present first attempts to tackle this problem\nwithin a Wilsonian-type renormaliz ation group framework\, where modes\nwith decreasing momenta are integrate d out successively.\n \n[1] Sur and Lee\, PRB 91\, 125136 (2015)\n\nContac t Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Patrick Neven DTSTART;TZID=Europe/Berlin:20150619T140000 DTEND;TZID=Europe/Berlin:20150619T153000 DTSTAMP:20260527T090436Z UID:0000000699@events.thp.uni-koeln.de DESCRIPTION:Patrick Neven\n\nPhD defense\n\n\n\nContact Person: not specif ied LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Johanna Kleinen DTSTART;TZID=Europe/Berlin:20150626T140000 DTEND;TZID=Europe/Berlin:20150626T153000 DTSTAMP:20260527T090436Z UID:0000000704@events.thp.uni-koeln.de DESCRIPTION:Johanna Kleinen\n\nOn the effect of a single magnetic impurity at the edge of a 2-dimensional topological insulator (Master Colloquium)\ n\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | David Luitz DTSTART;TZID=Europe/Berlin:20150703T130000 DTEND;TZID=Europe/Berlin:20150703T143000 DTSTAMP:20260527T090436Z UID:0000000654@events.thp.uni-koeln.de DESCRIPTION:David Luitz\, Toulouse\n\nMany body localization in the random field Heisenberg chain\n\n In this talk\, I will give an introduction to the phenomenon of many body localization and its differences from single p article Anderson\nlocalization. Then\, I discuss our recent exact diagonal ization results of the many body localization (MBL) transition in the rand om field Heisenberg chain and present in particular the energy vs\ndisorde r strength phase diagram that was obtained from various estimators. The ph ase boundary is strongly energy dependent\, thus providing evidence for an extensive mobility edge. At low disorder strength\, eigentstates are ergo dic and can be described by GOE statistics\, while in the strong field pha se\, they are localized and show Poisson statistics. In the MBL phase\, th e eigenstate\nthermalization hypothesis is no longer fulfilled.\n\nIf time permits\, I will provide an outlook on our current work\, where we\nlook at the exact time evolution of initial product states.\n\nReference:\nLuit z\, D. J.\, Laflorencie\, N. & Alet\, F.\nMany-body localization edge in t he random-field Heisenberg chain.\nPhys. Rev. B 91\, 081103 (2015).\n\nCon tact Person: Simon Trebst LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Roman Orus DTSTART;TZID=Europe/Berlin:20150710T141500 DTEND;TZID=Europe/Berlin:20150710T154500 DTSTAMP:20260527T090436Z UID:0000000668@events.thp.uni-koeln.de DESCRIPTION:Roman Orus\, University of Mainz\n\nEntanglement\, tensor netw orks\, and topological quantum order\n\nTopological order in a 2d quantum matter can be determined by the topological contribution to the entangleme nt Renyi entropies. However\, when close to a quantum phase transition\, i ts calculation becomes cumbersome. In this talk I will show how topologica l phase transitions in 2d systems can be much better assessed by multipart ite entanglement\, as measured by the topological geometric entanglement o f blocks. Specifically\, I will present an efficient tensor network algori thm based on Projected Entangled Pair States (PEPS) to compute this quanti ty for a torus partitioned into cylinders\, and then use this method to fi nd sharp evidence of topological phase transitions in 2d systems with a st ring-tension perturbation. When compared to tensor network methods for Ren yi entropies\, this approach produces almost perfect accuracies close to c riticality and\, on top\, is orders of magnitude faster. Moreover\, I will show how the method also allows the identification of Minimally Entangled States (MES)\, thus providing a very efficient and accurate way of extrac ting the full topological information of a 2d quantum lattice model from t he multipartite entanglement structure of its ground states. If time allow s I will also present briefly other ongoing projects at our group involvin g the use of tensor networks to study large-spin Kagome quantum antiferrom agnets\, 1d symmetry-protected topological order\, continuous unitary tran sformations\, and (1+1)d lattice gauge theories.\n\n\nContact Person: Joha nnes Helmes LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Oleg Tretiakov DTSTART;TZID=Europe/Berlin:20150714T100000 DTEND;TZID=Europe/Berlin:20150714T113000 DTSTAMP:20260527T090436Z UID:0000000703@events.thp.uni-koeln.de DESCRIPTION:Oleg Tretiakov\, Tohoku University\n\nAntiferromagnetic Skyrmi ons\n\nManipulating small spin textures\, which can serve as bits of infor mation\, by electric current is one of the main challenges in the field of spintronics. Ferromagnetic skyrmions recently attracted a lot of attentio n because they are small in size and are better than domain walls at avoid ing pinning while moved by electric current. Meanwhile\, ferromagnetic sky rmions still have disadvantages such as the presence of stray fields and t ransverse dynamics\, making them harder to employ for spintronic applicati ons. In this work\, we propose a novel topological object: the antiferroma gnetic (AFM) skyrmion. This topological texture has no stray fields and we show that its dynamics are faster compared to its ferromagnetic analogue. We obtain the dependence of AFM skyrmion radius on the strength of Dzyalo shinskii-Moriya interaction coming from relativistic spin-orbit effects an d temperature. We find that the thermal properties\, e.g. such as the AFM skyrmion radius and diffusion constant\, are rather different from those f or ferromagnetic skyrmions. More importantly\, we show that due to unusual topology the AFM skyrmions do not have a velocity component transverse to the current and thus may be perfect candidates for spintronic application s.\n\nContact Person: Markus Garst LOCATION:Seminar Room 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Andrew Mitchell DTSTART;TZID=Europe/Berlin:20150724T140000 DTEND;TZID=Europe/Berlin:20150724T153000 DTSTAMP:20260527T090436Z UID:0000000705@events.thp.uni-koeln.de DESCRIPTION:Andrew Mitchell\, Utrecht University\n\nKondo blockade conduct ance through single-molecule junctions\n\n\n\nContact Person: Ralf Bulla LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Dimitri Pimenov DTSTART;TZID=Europe/Berlin:20150807T140000 DTEND;TZID=Europe/Berlin:20150807T153000 DTSTAMP:20260527T090436Z UID:0000000740@events.thp.uni-koeln.de DESCRIPTION:Dimitri Pimenov\, LMU / TU Munich\n\nFermi-Edge polaritons wit h finite hole mass\n\n\n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Johannes Reuther DTSTART;TZID=Europe/Berlin:20150824T140000 DTEND;TZID=Europe/Berlin:20150824T150000 DTSTAMP:20260527T090436Z UID:0000000743@events.thp.uni-koeln.de DESCRIPTION:Johannes Reuther\, FU Berlin\n\nClassification of spin liquids on the square lattice with strong spin-orbit coupling\n\nThe investigatio n of spin liquids is a fascinating field in condensed\nmatter physics that is increasingly motivated by experiments. Exhaustive\nclassifications of spin liquids have been carried out in several systems\,\nparticularly when full SU(2) spin-rotation symmetry is present. Systematic\nstudies that ex plore strongly spin-orbit-coupled magnetic compounds (for\nwhich there are many experimental examples) are\, however\, relatively\nscarce. We report on a classification of Z_2 spin liquids on the square\nlattice when SU(2) spin symmetry is maximally lifted. Using projective\nsymmetry group metho ds\, we find that\, surprisingly\, the lifting of spin\nsymmetry yields va stly more spin liquid states compared to SU(2)-invariant\nsystems. A gener ic feature of the SU(2)-broken case is that the spinons\nnaturally undergo p+ip pairing\; consequently\, many of these Z_2 spin\nliquids feature a t opologically nontrivial spinon band structure\nsupporting gapless Majorana edge states. These boundary modes are often\nprotected by a combination o f time reversal and lattice symmetries and\nhence resemble recently propos ed topological crystalline superconductors.\n\nContact Person: Simon Trebs t LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Philipp Weiss DTSTART;TZID=Europe/Berlin:20150924T140000 DTEND;TZID=Europe/Berlin:20150924T153000 DTSTAMP:20260527T090436Z UID:0000000752@events.thp.uni-koeln.de DESCRIPTION:Philipp Weiss\, Karlsruhe Institute for Technology\n\nInterfer ence of quantum critical excitations and soft diffusive modes in a disorde red antiferromagnetic metal\n\n\n\nContact Person: Achim Rosch LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Bela Bauer DTSTART;TZID=Europe/Berlin:20150925T140000 DTEND;TZID=Europe/Berlin:20150925T153000 DTSTAMP:20260527T090436Z UID:0000000751@events.thp.uni-koeln.de DESCRIPTION:Bela Bauer\, Microsoft Station Q\n\nTopological Crystalline Bo se Insulators in Two Dimensions\n\n\n\nContact Person: Simon Trebst LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Jamir Marino DTSTART;TZID=Europe/Berlin:20151009T140000 DTEND;TZID=Europe/Berlin:20151009T153000 DTSTAMP:20260527T090436Z UID:0000000757@events.thp.uni-koeln.de DESCRIPTION:Jamir Marino\, TU Dresden\n\nDriven Markovian Quantum Critical ity\n\nWe identify a new universality class in one-dimensional driven open quantum systems with a dark state. Salient features are the persistence o f both the microscopic non-equilibrium conditions as well as the quantum c oherence of dynamics close to criticality. This provides a non-equilibrium analogue of quantum criticality\, and is sharply distinct from more gener ic driven systems\, where both effective thermalization as well as asympto tic decoherence ensue\, paralleling classical dynamical criticality. We qu antify universality by computing the full set of independent critical expo nents within a functional renormalization group approach.\n\n\n\nContact P erson: Philipp Strack LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Marijan Beg DTSTART;TZID=Europe/Berlin:20151023T140000 DTEND;TZID=Europe/Berlin:20151023T153000 DTSTAMP:20260527T090436Z UID:0000000758@events.thp.uni-koeln.de DESCRIPTION:Marijan Beg\, University of Southampton\n\nGround state search \, hysteretic behaviour\, reversal mechanism\, and normal modes of skyrmio nic textures in confined helimagnetic nanostructures\n\nMagnetic skyrmions have the potential to provide solutions for low-power\, high-density data storage and processing. One of the major challenges in developing skyrmio n-based devices is the skyrmions' magnetic stability in confined helimagne tic nanostructures. Through a systematic study of equilibrium states\, usi ng a full three-dimensional micromagnetic model including demagnetisation effects\, we demonstrate that skyrmionic textures are the lowest energy st ates in helimagnetic thin film nanostructures at zero external magnetic fi eld and in absence of magnetocrystalline anisotropy. We also report the re gions of metastability for non-ground state equilibrium configurations. We show that bistable skyrmionic textures undergo hysteretic behaviour betwe en two energetically equivalent skyrmionic states with different core orie ntation\, even in absence of both magnetocrystalline and demagnetisation-b ased shape anisotropies\, suggesting the existence of novel Dzyaloshinskii -Moriya-based shape anisotropy. We also show that the skyrmionic texture c ore reversal dynamics is facilitated by the Bloch point occurrence and pro pagation. Finally\, we report the resonance frequencies and corresponding normal modes of all identified equilibrium states as well as how the reson ance frequencies change depending on both the external magnetic bias field and disk sample diameter.\n\nContact Person: Markus Garst LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Yoshio Kuramoto DTSTART;TZID=Europe/Berlin:20151026T161500 DTEND;TZID=Europe/Berlin:20151026T174500 DTSTAMP:20260527T090436Z UID:0000000785@events.thp.uni-koeln.de DESCRIPTION:Yoshio Kuramoto\, Institute of Materials Structure Science KE K\, Tsukuba\, Japan\n\nOrthogonality and exciton correlations leading to K ondo-like effect\n\nIn certain Sm systems with mixed valence such as SmOs4 Sb12 and\nSmT2Al20 with T=Ti\, V\, Cr\, Ta\, etc\, the resistivity and spe cific heat\nshow behaviors reminiscent of the Kondo effect. However\, the \nbehaviors are almost independent of applied magnetic field. We\nascribe the Kondo-like behavior to charge correlations. Acccoding to\nour model\ , the effective hybridization of Sm 4f-electrons is reduced\nby the orthog onality effect with the Coulomb interaction U between 4f\nand conduction e lectrons. The Coulomb interaction also acts to\nenhance the hybridization via the exciton-like correlation. The\northogonality effect becomes domin ant as U and/or the number of\nconduction channels increases\, and eventua lly makes the effective\nhybridization vanish. We combine the continuous- time Monte Carlo\ncalculation and the analytic theory to derive the dynami cs in the wide\ntemperature range.\n\nContact Person: Achim Rosch LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Torsten Karzig DTSTART;TZID=Europe/Berlin:20151030T140000 DTEND;TZID=Europe/Berlin:20151030T150000 DTSTAMP:20260527T090436Z UID:0000000782@events.thp.uni-koeln.de DESCRIPTION:Torsten Karzig\, Microsoft Station Q\n\nSteps towards robust q uantum computation with Majorana bound states\n\nBraiding of Majorana zero modes provides a promising platform for quantum information processing. S trictly speaking\, however\, the scheme relies on infinite braiding times as it utilizes the adiabatic limit. I will discuss how to minimize nonadia batic errors for finite braiding times by finding an optimal protocol for the Majorana movement or adding so-called counter-diabatic terms to the Ha miltonian.\n\nIn the second part of the talk I will present a scheme to su bstantially increase the robustness of a Majorana pi/8 phase gate\, which is a missing ingredient when implementing universal quantum computation us ing Majorana bound states.\n\nContact Person: Maria Hermanns LOCATION:0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Ori Alberton DTSTART;TZID=Europe/Berlin:20151118T140000 DTEND;TZID=Europe/Berlin:20151118T153000 DTSTAMP:20260527T090436Z UID:0000000793@events.thp.uni-koeln.de DESCRIPTION:Ori Alberton\, Weizmann Institute\n\nFate of the one-dimension al Ising quantum critical point strongly coupled to a gapless phonon\n\nTh e problem of a quantum Ising degree of freedom coupled to a gapless bosoni c mode appears naturally in many one dimensional systems\, yet surprisingl y little is known how such a coupling affects the Ising quantum critical p oint. We investigate the fate of the critical point in a regime\, where th e weak coupling RG indicates a flow toward strong coupling. Using renormal ization group analysis and numerical density matrix renormalization group (DMRG) calculations we show that quantum fluctuations near the critical po int cause phase separation on an emergent long scale\, and the transition becomes first order. This suggests the existence of a tricritical point wi th potentially exotic properties.\n\nContact Person: Sebastian Diehl LOCATION:Seminaroom 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Michael Scherer DTSTART;TZID=Europe/Berlin:20151120T140000 DTEND;TZID=Europe/Berlin:20151120T153000 DTSTAMP:20260527T090436Z UID:0000000780@events.thp.uni-koeln.de DESCRIPTION:Michael Scherer\, University of Heidelberg\n\nCompetition of d ensity waves and quantum multicritical behavior in Dirac materials\n\nI di scuss the competition of spin- and charge-density waves and their quantum multicritical behavior for the semimetal-insulator transitions of low-dime nsional Dirac fermions. Employing the effective Gross-Neveu-Yukawa theory with two order parameters as a model for graphene and a growing number of other two-dimensional Dirac materials allows us to describe the physics ne ar the multicritical point at which the semimetallic and the two ordered p hases meet. With the functional renormalization group approach\, we reveal a complex structure of fixed points. Their the stability properties decis ively depend on the number of Dirac fermions Nf. We give estimates for the critical exponents and observe crucial quantitative corrections as compar ed to a previous first-order epsilon expansion. For small Nf\, the univers al behavior near the multicritical point is determined by the chiral Heise nberg universality class supplemented by a decoupled\, purely bosonic\, Is ing sector. At large Nf\, a novel fixed point with nontrivial couplings be tween all sectors becomes stable. At intermediate Nf\, including the graph ene case (Nf=2) no stable and physically admissible fixed point exists. We therefore suggest that Graphene's phase diagram in the vicinity of the in tersection between the semimetal\, antiferromagnetic and staggered density phases is governed by a triple point exhibiting first-order transitions.\ n\nContact Person: Philipp Strack LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Manuel Zohlen DTSTART;TZID=Europe/Berlin:20151210T084500 DTEND;TZID=Europe/Berlin:20151210T093000 DTSTAMP:20260527T090436Z UID:0000000798@events.thp.uni-koeln.de DESCRIPTION:Manuel Zohlen\n\nVortex crystallization in a bilayer Heisenber g-Kitaev model\n\n\n\nContact Person: Simon Trebst LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Stephanie Matern DTSTART;TZID=Europe/Berlin:20151211T140000 DTEND;TZID=Europe/Berlin:20151211T150000 DTSTAMP:20260527T090436Z UID:0000000773@events.thp.uni-koeln.de DESCRIPTION:Stephanie Matern\n\nUnconventional magnetism in spin-orbit ent angled Mott insulators (Master Colloquium)\n\n\n\nContact Person: not spec ified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Wilfried Michel DTSTART;TZID=Europe/Berlin:20151211T150000 DTEND;TZID=Europe/Berlin:20151211T160000 DTSTAMP:20260527T090436Z UID:0000000799@events.thp.uni-koeln.de DESCRIPTION:Wilfried Michel\n\nFinite-Temperature Sensitivity of Entanglem ent Spectra and Their Numerical Reconstruction from Renyi Entropies (Maste r Colloquium)\n\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Peter Zoller DTSTART;TZID=Europe/Berlin:20151214T160000 DTEND;TZID=Europe/Berlin:20151214T173000 DTSTAMP:20260527T090436Z UID:0000000786@events.thp.uni-koeln.de DESCRIPTION:Peter Zoller\, University of Innsbruck\n\nDriven Dissipative O pen Many-Body Systems in Quantum Optics \n\n\n\nContact Person: Achim Rosc h LOCATION:HS II END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Arijeet Pal DTSTART;TZID=Europe/Berlin:20151218T140000 DTEND;TZID=Europe/Berlin:20151218T153000 DTSTAMP:20260527T090436Z UID:0000000779@events.thp.uni-koeln.de DESCRIPTION:Arijeet Pal\, University of Oxford\n\nFinite temperature mobil ity edge in many-body localized systems\n\nThe ergodic hypothesis for an i solated quantum system has been a subject of intense investigation in rece nt years. Under what conditions does a quantum system thermalize in the ab sence of a heat bath? It has been argued that in the presence of strong di sorder\, a system loses its ability to equilibrate itself even at infinite temperature\, a phenomena now known as many-body localization (MBL). I wi ll review the basic notions of this new phase of matter characterized by i ts dynamics. Due to the violation of equilibrium statistical physics in th is phase\, MBL protects topological and symmetry-breaking orders in situat ions where they are destroyed at thermal equilibrium.\n\nIn this talk I wi ll discuss the phase transition between MBL and ergodic phases tuned by en ergy density\, leading to a finite temperature mobility edge. As concrete examples I will focus on the one-dimensional random-field Heisenberg and t he infinite-dimensional quantum random energy models. The latter has been a useful mean-field model for analyzing the thermodynamic spin-glass trans ition. Its tractability allows the comparison between analytical and numer ical study of a finite temperature mobility edge.\n\nContact Person: Phili pp Strack LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | David Mesterhazy & Florian Hebenstreit DTSTART;TZID=Europe/Berlin:20151218T100000 DTEND;TZID=Europe/Berlin:20151218T113000 DTSTAMP:20260527T090436Z UID:0000000803@events.thp.uni-koeln.de DESCRIPTION:David Mesterhazy & Florian Hebenstreit\, Universitity of Bern \n\nDissipative dynamics of Bose-Einstein condensation and entanglement ge neration\n\nWe elaborate on a proposal for the state preparation of quantu m many-body systems by engineered dissipation. Specifically\, we discuss t he purely dissipative dynamics of a large system of s = 1/2 quantum spins or\, equivalently\, hard-core bosons on a regular lattice. In the first pa rt of the talk\, we introduce the underlying quantum master equation (Lind blad equation) and exemplify how it can be used to determine the equations of motion for correlation functions. In the second part of the talk\, we resolve the real-time dynamics of the dissipative process. This allows us to identify different characteristic time scales for the dynamics for whic h we determine their finite-size scaling. We introduce the concept of cumu lative entanglement distribution to quantify multi-particle entanglement a nd show that the considered protocol serves as an efficient method to prep are a macroscopically entangled Bose-Einstein condensate.\n\nContact Perso n: Sebastian Diehl LOCATION:Seminar Room 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Marc Schulz DTSTART;TZID=Europe/Berlin:20160108T140000 DTEND;TZID=Europe/Berlin:20160108T153000 DTSTAMP:20260527T090436Z UID:0000000796@events.thp.uni-koeln.de DESCRIPTION:Marc Schulz\, University of Minnesota\n\nFrustrated topologica l symmetry breaking: geometrical frustration and anyon condensation\n\n\n\ nContact Person: Johannes Helmes LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Igor Mekhov DTSTART;TZID=Europe/Berlin:20160115T140000 DTEND;TZID=Europe/Berlin:20160115T153000 DTSTAMP:20260527T090436Z UID:0000000788@events.thp.uni-koeln.de DESCRIPTION:Igor Mekhov\, Oxford University\n\nUsing quantized light in ul tracold atom problems\n\nAlthough light is the main tool in quantum gas ph ysics\, its quantumness is often neglected. We show that elevating light t o a quantum variable leads to a plethora of novel many-body phenomena\, un obtainable in classical optical setups. \n First\, we prove that the quan tum backaction of a weak global measurement can efficiently compete with s tandard short-range processes in a strongly correlated system (ultracold b osons or fermions in an optical lattice)\, leading to novel phenomena. We demonstrate generation of the multimode generalizations of Schroedinger ca t and NOON states\, nonlocal quantum Zeno dynamics\, and non-Hermitian pro cesses without the need of postselection. For fermions\, we show the measu rement-induced antiferromagnetic states\, as well as the protection and br eak-up of strongly interacting fermion pairs. The backaction results in th e generation of genuinely multipartite entangled modes of matter waves\, w hich show non-Gaussian properties beyond quantum optical analogues. \n Se cond\, trapping quantum gases inside a high-Q cavity\, creates a paradigm of quantum optical lattices. We demonstrate the emergence of novel many-bo dy phases: delocalized dimers\, trimers\, etc. of matter waves\, even beyo nd the density orders such as density waves and supersolids. We show that cavity QED of strongly correlated systems can efficiently simulate systems with short- and long-range interactions\, while still profiting from the collective enhancement of the light-matter interaction.\n\nContact Person: Philipp Strack LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Spiros Sotiriadis DTSTART;TZID=Europe/Berlin:20160125T123000 DTEND;TZID=Europe/Berlin:20160125T134500 DTSTAMP:20260527T090436Z UID:0000000812@events.thp.uni-koeln.de DESCRIPTION:Spiros Sotiriadis\, University of Pisa\n\nEquilibration and me mory preservation after a quantum quench\n\nResearch in out-of-equilibrium quantum physics has recently revealed relaxation towards a non-thermal st atistical ensemble (Generalised Gibbs Ensemble or shortly GGE) that retain s more memory of the initial state than the conventional thermal ensemble. The information content of this ensemble remains however a riddle. By ana lytically studying the time evolution after abrupt changes (quantum quench es) in extended one-dimensional quantum systems\, we demonstrate relaxatio n according to the GGE in various different settings and specify the infor mation that survives in the stationary state. In the case of evolution und er a gapless non-interacting Hamiltonian on the other hand\, we observe th e failure of the GGE and find evidence of a novel type of equilibration ch aracterised by the preservation of non-Gaussian correlations of the initia l state. We propose an experimental check of our predictions based on curr ent experimental techniques.\n\nContact Person: Sebastian Diehl LOCATION:Seminarroom 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Tobias Grass DTSTART;TZID=Europe/Berlin:20160127T140000 DTEND;TZID=Europe/Berlin:20160127T153000 DTSTAMP:20260527T090436Z UID:0000000813@events.thp.uni-koeln.de DESCRIPTION:Tobias Grass\, Institut de Ciencies Fotoniques\, Barcelona\n\n Make ions count: solving computational problems via quantum simulation\n\n Trapped ions provide flexible emulators of spin Hamiltonians. In this talk \, I will motivate to use ions for an implementation of a Mattis-type spin glass model. Finding the ground state of this model is equivalent to the optimization process in the number partitioning problem - a potentially NP -hard computational task. A transverse magnetic field introduces quantum e ffects\, and opens the door to quantum annealing. A numerical study of the system dynamics demonstrates the feasibility of this approach.\n\nContact Person: Sebastian Diehl LOCATION:Seminaroom 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Markus Grassl DTSTART;TZID=Europe/Berlin:20160128T120000 DTEND;TZID=Europe/Berlin:20160128T131500 DTSTAMP:20260527T090436Z UID:0000000807@events.thp.uni-koeln.de DESCRIPTION:Markus Grassl\, University Erlangen-Nuernberg\n\nEntanglement Polytopes of Some Five Qubit States\n\nThe local spectra of quantum states in SLOCC classes of n qubit states\ngive rise to polytopes in n-dimension al real space. While for more than\nthree qubits there are infinitely SLOC C classes\, there are always\nfinitely many so-called entanglement polytop es. The entanglement\npolytopes can be computed from a generating set of a ll covariants with\nrespect to the group of local transformations. Further more\, a duality\nbetween entanglement polytopes and algebraic varieties y ields a\ndescription of different types of entanglement. In the talk\, we will\nillustrate this approach and present results for entanglement polyto pes\nfor some five qubit states.\n\nContact Person: David Gross LOCATION:Seminar Room 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Loic Henriet DTSTART;TZID=Europe/Berlin:20160209T100000 DTEND;TZID=Europe/Berlin:20160209T110000 DTSTAMP:20260527T090436Z UID:0000000822@events.thp.uni-koeln.de DESCRIPTION:Loic Henriet\, Ecole Polytechnique\, France\n\nNon-equilibrium phenomena in light-matter systems\n\nRecent experimental developments off er platforms to investigate the interaction between light and matter at th e quantum level\, encouraging the buildup of theoretical tools to describe their dynamics. The great control over the system parameters also permits to tune many-body Hamiltonians\, opening the way to explore novel quantum phases. In this talk\, I will first introduce a nano-engine device compos ed of a quantum dot coupled to external environments\, and show that vacuu m symmetry breaking generates a rectified current flowing through the devi ce. I will then present a stochastic approach which aims at computing the out-of-equilibrium dynamics of spin-boson models. This approach permits to explore the strong coupling regime of the Rabi model\, which is the simpl est model of interaction between light and matter\, and to investigate the quantum phase transition in the ohmic spinboson model\, which describes a two-level system interacting with a dissipative environment. I will also present an hybrid setup comprising a double quantum dot coupled to a micro wave cavity\, which was realized recently. This system produces a highly e ntangled state of light and matter in relation to Kondo physics. \n\nConta ct Person: Sebastian Diehl LOCATION:Seminarroom 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Pavel Ostrovsky DTSTART;TZID=Europe/Berlin:20160212T140000 DTEND;TZID=Europe/Berlin:20160212T153000 DTSTAMP:20260527T090436Z UID:0000000810@events.thp.uni-koeln.de DESCRIPTION:Pavel Ostrovsky\, MPI Stuttgart\n\nAnomalous Hall effect in we akly disordered ferromagnets\n\nAnomalous Hall effect arises in systems wi th both spin-orbit coupling and magnetization. Generally\, there are three mechanisms contributing to anomalous Hall conductivity: intrinsic\, side jump\, and skew scattering. The standard diagrammatic approach to the anom alous Hall effect is limited to computation of ladder diagrams. We demonst rate that this approach is insufficient. An important additional contribut ion comes from diagrams with a single pair of intersecting disorder lines. This contribution constitutes an inherent part of skew scattering on pair s of closely located defects and essentially modifies previously obtained results for anomalous Hall conductivity. We argue that this statement is g eneral and applies to all models of anomalous Hall effect. We illustrate i t by an explicit calculation for two-dimensional massive Dirac fermions an d for the Rashba ferromagnet model with weak disorder. In the case of Dira c electrons\, inclusion of the diagrams with crossed impurity lines revers es the sign of the skew scattering term and strongly suppresses the total Hall conductivity at high electron concentrations. In the 2D Rashba model\ , the proposed mechanism provides the only contribution to the anomalous H all conductivity in the most relevant metallic regime.\n\n\nContact Person : Dmitry Bagrets LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Michael Brockmann DTSTART;TZID=Europe/Berlin:20160226T140000 DTEND;TZID=Europe/Berlin:20160226T153000 DTSTAMP:20260527T090436Z UID:0000000802@events.thp.uni-koeln.de DESCRIPTION:Michael Brockmann\, MPI PKS Dresden\n\nEquilibration in the sp in-1/2 Heisenberg chain after an interaction quench\n\n\n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Michael Walter DTSTART;TZID=Europe/Berlin:20160304T140000 DTEND;TZID=Europe/Berlin:20160304T153000 DTSTAMP:20260527T090436Z UID:0000000831@events.thp.uni-koeln.de DESCRIPTION:Michael Walter\, Stanford University\n\nRandom tensor networks and holographic duality\n\nTensor networks provide a natural framework fo r studying\nbulk-to-boundary or holographic correspondences. In this talk\ , we will\nexplore the holographic properties of random tensor networks wi th\nlarge bond dimensions. We find that they realize many of the\ninterest ing structural features of the AdS/CFT correspondence in\nquantum gravity: Entanglement entropies of boundary subsystem\ncorrespond to minimal domai n walls in the bulk\, and the physics in the\ndomain is encoded faithfully in the boundary subsystem. Increasing the\nentanglement in the bulk ultim ately creates the analog of a black\nhole\, with an associated Hawking-Pag e phase transition. All this can\nbe understood by mapping the statistical properties of random tensors\nto the partition function of classical ferr omagnetic Ising models.\nFrom the perspective of quantum information theor y\, random tensor\nnetworks implement quantum error-correcting codes with interesting\nlocality properties\, and their emergence can be understood a s an\nassisted form of entanglement distillation.\n\nContact Person: not s pecified LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Boye Buyens DTSTART;TZID=Europe/Berlin:20160307T140000 DTEND;TZID=Europe/Berlin:20160307T150000 DTSTAMP:20260527T090436Z UID:0000000838@events.thp.uni-koeln.de DESCRIPTION:Boye Buyens\, Ghent University\n\nGauge field theories: the Ha miltonian picture\n\nMotivated by the entanglement properties of low-energ y states of local Hamiltonians I introduce matrix product states (MPS) as a variational ansatz for the study of one dimensional quantum many-body sy stems. Then I apply the MPS formalism to study 1+1 dimensional QED\, also know as the massive Schwinger model. I explain how MPS are used to compute an approximation of the ground state and discuss its entanglement propert ies. Next\, MPS are used to study non-equilibrium dynamics by a quench in the form of a uniform background electric field. When the electric backgro und field is small\, the results are explained by investigating the low-en ergy spectrum of the Hamiltonian. For larger values of the quench we obser ve thermalisation. Finally\, I discuss how the MPS framework is generalise d to higher dimensions and can be used to simulate real-time evolution.\n\ nContact Person: Sebastian Diehl LOCATION:Seminarroom 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Jan Manousakis DTSTART;TZID=Europe/Berlin:20160318T140000 DTEND;TZID=Europe/Berlin:20160318T153000 DTSTAMP:20260527T090436Z UID:0000000826@events.thp.uni-koeln.de DESCRIPTION:Jan Manousakis\n\nField theory of statistical toplogical insul ators with chiral symmetry (Master defense)\n\n\n\nContact Person: not spe cified LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Ferdinand Brennecke DTSTART;TZID=Europe/Berlin:20160415T140000 DTEND;TZID=Europe/Berlin:20160415T153000 DTSTAMP:20260527T090436Z UID:0000000832@events.thp.uni-koeln.de DESCRIPTION:Ferdinand Brennecke\, University of Bonn\n\nEquation of state of the 2d Hubbard model\n\nQuantum gases of interacting fermionic atoms in optical lattices promise to shed new light on the low-temperature phases of Hubbard-type models\, such as Mott-insulating and spin-ordered phases o r possible d-wave superconductivity. We experimentally realize the two-dim ensional Hubbard model by loading a quantum degenerate two-component Fermi gas of 40K atoms into an anisotropic optical lattice geometry. Using high -resolution absorption imaging combined with radio-frequency spectroscopy we are able to resolve the in-situ distribution of singly and doubly occup ied lattice sites within a single two-dimensional layer.\n\nIn this talk\, I will report on the in-situ observation of the fermionic Mott insulator and a measurement of the equation of state of the repulsive Hubbard model in two dimensions which constitutes a benchmark for state-of-the-art theor etical approaches.\n\nContact Person: Philipp Strack LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Finn Lasse Buessen DTSTART;TZID=Europe/Berlin:20160429T140000 DTEND;TZID=Europe/Berlin:20160429T150000 DTSTAMP:20260527T090436Z UID:0000000867@events.thp.uni-koeln.de DESCRIPTION:Finn Lasse Buessen\, University of Cologne\n\nFunctional Renor malization Group Studies of Spin-Orbit Entangled j=1/2 Mott Insulators (Ma ster's Colloquium)\n\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Tomaz Prosen DTSTART;TZID=Europe/Berlin:20160513T140000 DTEND;TZID=Europe/Berlin:20160513T153000 DTSTAMP:20260527T090436Z UID:0000000874@events.thp.uni-koeln.de DESCRIPTION:Tomaz Prosen\, University of Ljubljana\n\nIntegrability of a d eterministic cellular automaton driven by stochastic boundaries\n\nWe prop ose an interacting many-body space-time-discrete Markov chain model\, whic h is composed of an integrable deterministic and reversible cellular autom aton (the rule 54 of [Bobenko et al\, CMP 158\, 127 (1993)]) on a finite o ne-dimensional lattice\, and local stochastic Markov chains at the two lat tice boundaries which provide chemical baths for absorbing or emitting the solitons. Ergodicity and mixing of this many-body Markov chain is proven for generic values of bath parameters\, implying existence of a unique non -equilibrium steady state. The latter is constructed exactly and explicitl y in terms of a particularly simple form of matrix product ansatz which is termed a patch ansatz. This gives rise to an explicit computation of obse rvables and k-point correlations in the steady state as well as the constr uction of a nontrivial set of local conservation laws. Feasibility of an e xact solution for the full spectrum and eigenvectors (decay modes) of the Markov matrix is suggested as well. We conjecture that such ideas can pave the road towards a theory of integrability of boundary driven classical d eterministic lattice systems.\n\nContact Person: Zala Lenarcic LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Lukas Janssen DTSTART;TZID=Europe/Berlin:20160518T110000 DTEND;TZID=Europe/Berlin:20160518T123000 DTSTAMP:20260527T090436Z UID:0000000871@events.thp.uni-koeln.de DESCRIPTION:Lukas Janssen\, TU Dresden\n\nSpontaneous breaking of Lorentz symmetry in QED3\n\nThe phase diagram of quantum electrodynamics in three space-time dimensions as a function of fermion flavor number N exhibits tw o well-known phases: at large N > Nc1 the system is in a conformal gapless state\, while for small N < Nc2 the fermions are expected to develop a dy namical mass due to spontaneous chiral symmetry breaking. Using epsilon ex pansion near the lower critical dimension of two\, in combination with the recent results on the generalization of the F theorem to continuous dimen sion\, we show that Nc1 > Nc2. There is therefore an intermediate range of values of N at which a third phase is stabilized. We demonstrate that thi s phase is characterized by spontaneous breaking of Lorentz symmetry\, in which a composite vector boson field acquires a vacuum expectation value w ith the fermions and the photon remaining massless.\n\nContact Person: Die trich Roscher LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Anne Nielsen DTSTART;TZID=Europe/Berlin:20160603T140000 DTEND;TZID=Europe/Berlin:20160603T153000 DTSTAMP:20260527T090436Z UID:0000000840@events.thp.uni-koeln.de DESCRIPTION:Anne Nielsen\, MPI-PKS Dresden\n\nFractional quantum Hall phys ics in lattice systems\n\nThe fractional quantum Hall effect\, which can b e realized in certain\ntwo-dimensional systems at low temperature and high magnetic field\, leads\nto many interesting properties\, such as the poss ibility to have anyonic\nquasiparticles that are neither bosons nor fermio ns. There is currently\nmuch interest in investigating the possibilities f or having fractional\nquantum Hall physics in lattice systems\, both becau se it may lead to new\nways to realize the effect\, and because the lattic e gives rise to new\nfeatures and opportunities. Here\, we propose a quite general approach\nbased on conformal field theory to obtain lattice fract ional quantum Hall\nmodels. The models have analytical ground states\, and we use Monte Carlo\nsimulations to compute\, e.g.\, topological entanglem ent entropies and shape\nand statistics of anyons. We also discuss how one can interpolate between\nlattice and continuum fractional quantum Hall mo dels and propose a scheme\nto implement a related model in ultracold atoms in optical lattices.\n\nContact Person: not specified LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Yin-Chen He DTSTART;TZID=Europe/Berlin:20160610T140000 DTEND;TZID=Europe/Berlin:20160610T153000 DTSTAMP:20260527T090436Z UID:0000000879@events.thp.uni-koeln.de DESCRIPTION:Yin-Chen He\, MPI-PKS Dresden\n\nSpin liquids on kagome lattic e and symmetry protected topological phase\n\nIn my talk I will introduce the spin liquid phases that occur in kagome antiferromagnets\, and discuss their physical origin that are closely related with the newly discovered symmetry protected topological phase (SPT). I will first present our numer ical (DMRG) study on the kagome XXZ spin model that exhibits two distinct spin liquid phases\, namely the chiral spin liquid and the kagome spin liq uid (the groundstate of the nearest neighbor kagome Heisenberg model). Bot h phases extend from the extreme easy-axis limit\, through SU(2) symmetric point\, to the pure easy-plane limit. The two phases are separated by a c ontinuous phase transition. Motivated by these numerical results\, I will then focus on the easy-axis kagome spin system\, and reformulate it as a l attice gauge model. Such formulation enables us to achieve a controlled th eoretical description for the spin liquid phases. We then show that the ch iral spin liquid is indeed a gauged U(1) SPT phase. On the other hand\, we also propose that the kagome spin liquid is a critical spin liquid phase\ , which can be considered as a gauged deconfined critical point between a SPT and a superfluid phase. \n\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Alexander Glaetzle DTSTART;TZID=Europe/Berlin:20160617T140000 DTEND;TZID=Europe/Berlin:20160617T153000 DTSTAMP:20260527T090436Z UID:0000000892@events.thp.uni-koeln.de DESCRIPTION:Alexander Glaetzle\, University of Innsbruck\n\nDesigning Quan tum Spin Models with Laser-Dressed Rydberg Atoms\n\nIn my talk I will star t with a review of our recent work on realizing a broad class of lattice s pin-1/2 models with cold alkali atoms stored in optical or magnetic trap a rrays. In particular\, we exploit the strong angular dependence of van der Waals interactions between high angular momentum Rydberg states. Together with the possibility of designing step-like potentials we can implement A belian gauge theories in a series of geometries\, which could be demonstra ted within state of the art experiments. The resulting energy scales of in teractions compare well with typical temperatures and decoherence time-sca les\, making the exploration of exotic forms of quantum magnetism\, includ ing emergent gauge theories\, compass models and quantum spin ice models\, accessible within state-of-the-art experiments.\n\nContact Person: not sp ecified LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Elio Koenig DTSTART;TZID=Europe/Berlin:20160624T140000 DTEND;TZID=Europe/Berlin:20160624T153000 DTSTAMP:20260527T090436Z UID:0000000863@events.thp.uni-koeln.de DESCRIPTION:Elio Koenig\, University of Wisconsin\, Madison\n\nAnomalous H all effect in topological insulators and superconductors\n\nIn the first p art of the talk\, the recent advance in the theory of the anomalous Hall e ffect is reviewed. Remarkably\, it was shown that diagrams with crossed im purity lines yield an anomalous Hall conductivity that is independent of i mpurity concentration\, and thus is of the same order as other known extri nsic side jump and skew scattering terms. Based on a semiclassical interpr etation\, we explain that such diagrams represent diffractive skew scatter ing contributions originating from rare two-impurity complexes. \n\nNext\, results for the anomalous Hall conductivity sigma_xy of the surface state s in cubic topological Kondo insulators are presented. We consider a gener ic model for the surface states with three Dirac cones on the (001) surfac e: The Fermi velocity\, the Fermi momentum and the Zeeman energy in differ ent Dirac pockets may be unequal. The microscopic impurity potential media tes mixed intra and interband extrinsic scattering processes. We discuss v arious special cases of our results and the experimental relevance of our study in the context of the recent hysteretic magnetotransport data in SmB 6 samples.\n\nThe last part of the talk is devoted to our recent study of the temperature dependent anomalous ac Hall conductance sigma_xy(omega\, T ) for a 2D chiral p-wave superconductor [3]. This quantity determines the polar Kerr effect\, as it was observed in Sr2RuO4. We concentrate on a sin gle band model with generic\, isotropic dispersion relation subjected to r are\, weak impurities treated in the Born approximation. Again\, the empha sis is on diffractive skew scattering from quantum impurity complexes. It is explicitly shown\, that this effect contributes to leading order in imp urity concentration and is thus comparable to earlier results within the s ame model.\n\n\n\nContact Person: Dmitry Bagrets LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Marcello Dalmonte DTSTART;TZID=Europe/Berlin:20160630T110000 DTEND;TZID=Europe/Berlin:20160630T123000 DTSTAMP:20260527T090436Z UID:0000000890@events.thp.uni-koeln.de DESCRIPTION:Marcello Dalmonte\, University of Innsbruck\n\nEffects of clus tering in soft-shoulder Hubbard models: from supersymmetric critical point s to unconventional quantum liquid.\n\nIn this seminar\, I will discuss ho w complementing the Bose-Hubbard model with soft-shoulder interactions all ows for the stabilization of exotic state of matters which\, in one- and t wo-dimensions\, break the typical Luttinger and Landau liquid paradigms. I n the first part talk\, I will present discuss the basic classical statist ical mechanics ingredients of such potentials\, which support cluster solu tions with extensive ground state degeneracy. Using a combination of field theoretical and numerical approaches\, the phase diagram of the model wil l be presented. In particular\, I will focus on the existence of a Cluster Luttinger liquid phase\, which cannot be captured using conventional ‘c oarse graining’ schemes of Abelian bosonization\, and show how this phas e is separated by a conventional Luttinger liquid via a phase transition w ith emergent conformal supersymmetry. In the second part of the talk\, I w ill discuss the fate of such states and transitions in two-dimensions usin g numerical simulations. In this context\, strong soft-shoulder interactio ns lead to a dramatic change of the ‘Bose surface’\, and stabilize a p hase with no broken symmetry but still displaying quasi-long-range coheren ce\, of Bose-metal type. The mechanism for the stabilization of such exoti c liquids is clusterization\, which defines a low-energy manifold displayi ng extensive ground state degeneracy and\, and the same time\, suppress su perfluid order. Finally\, I will present some considerations on the experi mental realization of both one- and two-dimensional cases using laser-dres sed Rydberg atoms. \n\nContact Person: Jamir Marino LOCATION:Seminar room 0.01\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Darshan Joshi DTSTART;TZID=Europe/Berlin:20160630T120000 DTEND;TZID=Europe/Berlin:20160630T133000 DTSTAMP:20260527T090436Z UID:0000000908@events.thp.uni-koeln.de DESCRIPTION:Darshan Joshi\, TU Dresden\n\nCoupled-dimer magnets: From Heis enberg to Kitaev\n\n\n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Cedric Beny DTSTART;TZID=Europe/Berlin:20160706T160000 DTEND;TZID=Europe/Berlin:20160706T170000 DTSTAMP:20260527T090436Z UID:0000000906@events.thp.uni-koeln.de DESCRIPTION:Cedric Beny\, Hannover\n\nTensor networks and AdS/CFT \n\nI w ill introduce some basic facts about the AdS/CFT correspondance which may be relevant to tensor network models. The group of isometries of Anti de S itter space is also the group of Lorentzian conformal maps on its "boundar y at infinity". Similarly\, the isometries of Hyperbolic space or de Sitte r space form the Euclidean conformal group. Thinking of path integrals as continuous tensor networks\, one can see how the ground state of a quantum field theory in AdS space may be thought of as that of a conformal field theory on its boundary\, whose correlators are represented by tree tensor networks. TTNs also arise when computing correlators in MERA\, which can b e thought of as a discretisation of de Sitter space. Is there a formal rel ationship between these two pictures?\n\nContact Person: David Gross LOCATION:Seminar room 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Halil Cakir DTSTART;TZID=Europe/Berlin:20160708T140000 DTEND;TZID=Europe/Berlin:20160708T150000 DTSTAMP:20260527T090436Z UID:0000000907@events.thp.uni-koeln.de DESCRIPTION:Halil Cakir\, University of Heidelberg\n\nDynamics of the Tran sverse Field Ising Chain after a Sudden Quench\n\nDue to experimental adva nces in the preparation and control of \nultra-cold atomic gases\, there i s a widespread interest in the behaviour \nof quantum systems out of equil ibrium. A common way to probe quantum \nsystems for non-equilibrium phenom ena is given by sudden quenches. I \nwill present results concerning the d ynamics of the longitudinal spin \ncorrelation function after a sudden que nch in the Transverse Field Ising \nChain. A distinguishing feature of thi s model is that it exhibits a \nquantum critical point separating a ferrom agnetic from a paramagnetic \nphase. Furthermore\, the system can be expre ssed as a fermionic harmonic \noscillator\, which allows us to determine t he longitudinal correlation \nfunction after a sudden quench exactly by us ing Wick's theorem. In \nparticular\, I will concentrate on the behaviour of the longitudinal \ncorrelation function for quenches from an initially large external field \nto the vicinity of the quantum critical point withi n the paramagnetic \nphase. We conjectured a formula for the asymptotic be haviour in this \ncase and compared it to numerical calculations of the co rrelator. Based \non this conjectured formula\, we found that the decay of the correlation \nfunction is characterized by two correlation lengths an d that the \ncorrelation function attains its stationary values already at short \ndistances.\n\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Markus Mueller DTSTART;TZID=Europe/Berlin:20160712T140000 DTEND;TZID=Europe/Berlin:20160712T153000 DTSTAMP:20260527T090436Z UID:0000000897@events.thp.uni-koeln.de DESCRIPTION:Markus Mueller\, Paul-Scherrer Institut\n\nOn many-body mobili ty edges in interacting systems\n\nIn recent years\, many-body localizatio n and the prediction of a metal-insulator transition at finite temperature has attracted a lot of attention as a way to maintain permanent off-equil ibrium conditions in a thermodynamic\, but closed quantum many-body system . Such transitions\, driven by energy density (or ”temperature”)\, req uire the presence of a many-body mobility edge in energy\, that separates localized from ergodic states. I argue that for short range interactions t his scenario is beyond the control of perturbation theory and seems incons istent due to inclusions of the ergodic phase in the supposedly localized phase. Those inclusions are mobile and induce global delocalization. These considerations modify the phase diagrams for interacting systems both wit h and without quenched disorder. \n\nContact Person: Philipp Strack LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Christian Faber and Matthias Pukrop DTSTART;TZID=Europe/Berlin:20160715T140000 DTEND;TZID=Europe/Berlin:20160715T153000 DTSTAMP:20260527T090436Z UID:0000000905@events.thp.uni-koeln.de DESCRIPTION:Christian Faber and Matthias Pukrop\n\nBachelor colloquia\n\n\ n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Dario Poletti DTSTART;TZID=Europe/Berlin:20160720T160000 DTEND;TZID=Europe/Berlin:20160720T170000 DTSTAMP:20260527T090436Z UID:0000000918@events.thp.uni-koeln.de DESCRIPTION:Dario Poletti\, Singapore University of Technology and Design\ n\nGeometry of system-bath coupling and gauge fields in bosonic ladders: m anipulating currents and driving phase transitions \n\nQuantum systems in contact with an environment display a rich physics emerging from the inte rplay between dissipative and Hamiltonian terms. We consider a dissipative boundary driven ladder in presence of a gauge field. The dissipation stim ulates currents while the gauge field tends to steer the flow. We show tha t depending on the geometry of coupling to the baths and of the strength o f the gauge field\, non-equilibrium phase transitions emerge strongly modi fying the currents both in magnitude and spatial distribution. \n\nContact Person: Jamir Marino LOCATION:Seminarroom 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Laura Classen DTSTART;TZID=Europe/Berlin:20160722T140000 DTEND;TZID=Europe/Berlin:20160722T153000 DTSTAMP:20260527T090436Z UID:0000000893@events.thp.uni-koeln.de DESCRIPTION:Laura Classen\, University of Heidelberg\n\nInterplay between magnetism\, superconductivity\, and orbital order in 5-pocket model for ir on-based superconductors\n\nWe report the results of the full parquet reno rmalization group (pRG) analysis of the 5-pocket model for Fe-based super conductors (three hole pockets and two electron pockets). We depart from t he low-energy orbital model and use as input the fact that excitations nea r all five pockets are made out of xz\, yz\, and xy d-orbitals. We argue\ , based on symmetry that there are 40 different coupling constants which d escribe the interactions between low-energy fermions and flow under pRG. The pRG analysis reveals four stable fixed trajectories. They can be group ed into two classes\, where the 5-pocket model effectively reduces either to a 3-pocket or a 4-pocket one. We argue that in both cases superconducti vity wins over SDW if all five Fermi energies are small and pRG runs over a wide energy range. The resulting superconducting symmetry is !\n of s+- fo\n r\nm for both effective models\, but the magnitude of the gap differ s between the hole pockets at (0\,0) and (pi\,pi) in the 1Fe zone. SDW mag netism is of stripe type in the 3-pocket and of checkerboard type in the 4 -pocket case. Additionally a spontaneous orbital order develops before su perconductivity that splits the band degeneracy at high-symmetry points.\n \nContact Person: not specified LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Leon Schoonderwoerd DTSTART;TZID=Europe/Berlin:20161007T140000 DTEND;TZID=Europe/Berlin:20161007T153000 DTSTAMP:20260527T090436Z UID:0000000967@events.thp.uni-koeln.de DESCRIPTION:Leon Schoonderwoerd\, University of Amsterdam\n\nTensor networ k algorithms for 1D spin chains: DMRG and entanglement entropy minimizatio n\n\nTensor networks provide a novel and powerful way to think about and p erform calculations with many-body systems. This talk treats tensor networ ks in the form of Matrix Product states (MPS) and Matrix Product Operators (MPO)\, which are used for calculations on (1D) spin chains. Firstly\, De nsity Matrix Renormalization Group (DMRG) algorithms\, concerned with find ing the ground state and its energy. Secondly\, an approach for the minimi zation of entanglement entropy using unitary basis transformations is give n. The idea for this latter part is based on [1]\, but instead of a parame ter-based approach\, an environment network-based algorithm is used. The c ombination of the entropy minimization with DMRG is discussed. Results obt ained using the minimization algorithm are shown\, and the method's limita tions are discussed.\n\n[1] C. Krumnow\, L. Veis\, Ö. Legeza & J. Eisert\ , Fermionic orbital optimisation in tensor network states\, arXiv 1504.000 42v3\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Alex Kruchkov DTSTART;TZID=Europe/Berlin:20161014T140000 DTEND;TZID=Europe/Berlin:20161014T153000 DTSTAMP:20260527T090436Z UID:0000000948@events.thp.uni-koeln.de DESCRIPTION:Alex Kruchkov\, Ecole Polytechnique Federale de Lausanne\n\nQu antum Lightsaber: condensation of light in an ultrathin tube\n\nLight can be converted into a liquid\, a quantum liquid called Bose-Einstein condens ate\, where it nearly stops if travels in one dimension. In this talk\, I address a quasiequilibrium one-dimensional Bose-Einstein condensation of p hotons trapped in a microtube\, which is possible because the light modes have a cut-off frequency (a photon’s “mass”) and interact through di fferent processes of absorption\, emission\, and scattering on molecules a nd atoms. I discuss the conditions for the one-dimensional condensation of light and the role of photon- photon interactions in the system. This the oretical study is in the strong connection with the experiments of the Wei tz Quantum Optics group (University of Bonn).\n\nContact Person: Achim Ros ch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Rosario Fazio DTSTART;TZID=Europe/Berlin:20161017T160000 DTEND;TZID=Europe/Berlin:20161017T170000 DTSTAMP:20260527T090436Z UID:0000000934@events.thp.uni-koeln.de DESCRIPTION:Rosario Fazio\, ICTP\, Trieste\n\nSteady state phase diagram o f driven-dissipative systems\n\nThanks to the recent impressing experiment al progresses the investigation of non- equilibrium properties of driven-d issipative systems has entered the quantum world. Rydberg atoms in optical lattices\, systems of trapped ions\, exciton- polariton condensates\, col d atoms in cavities\, arrays of coupled QED cavities\, are probably the mo st intensively investigated experimental platforms in relation to this aim . I will discuss properties of phases and phase transitions in the steady state of these systems.\n\nContact Person: Jamir Marino LOCATION:Seminarroom 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Samuel Bieri DTSTART;TZID=Europe/Berlin:20161104T140000 DTEND;TZID=Europe/Berlin:20161104T153000 DTSTAMP:20260527T090436Z UID:0000000943@events.thp.uni-koeln.de DESCRIPTION:Samuel Bieri\, ETH Zurich / Sorbonne\n\nQuantum spin liquids i n frustrated magnets\n\nQuantum spin liquids are fascinating phases in qua ntum magnetism. Broad theoretical advances\, and fast progress in material s science have significantly advanced the field in recent years.\n\nAfter a general introduction to the subject\, I will talk about the projective s ymmetry group approach to the problem of classification of such exotic pha ses. In a second part\, I will present work on the theory for the kapellas ite material\, a spin S=1/2 Heisenberg antiferromagnet on the kagome latti ce. Finally\, I will discuss a highly intriguing phase that was recently c haracterized in the triangular spin S=1 compound BaNiSbO.\n\nSB et al\, PR B 93\, 094437 (2016).\nSB et al\, PRB 92\, 060407(R) (2015).\nB. Fak\, SB\ , et al\, arXiv:1610.03753 (2016).\n\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Junichi Iwasaki DTSTART;TZID=Europe/Berlin:20161125T140000 DTEND;TZID=Europe/Berlin:20161125T153000 DTSTAMP:20260527T090436Z UID:0000000993@events.thp.uni-koeln.de DESCRIPTION:Junichi Iwasaki\, University of Tokyo\n\nDeformation of Skyrmi on Crystal under Strain and under Driving Current\n\nManipulation of spin textures has been attracting a broad interest\nfrom the viewpoints of both fundamental physics and applications over\ndecades. In particular\, the c ontrol magnetic skyrmions is one of the\nhottest topics. In the first part of my talk\, I will talk about the\nstatic deformation of skyrmion crysta ls under uniaxial strain revealed\nby the Lorentz TEM observation. This ex perimental result is analyzed\nby the model with an anisotropic Dzyaloshin skii-Moriya interaction\,\nwhich shows a good agreement with the experimen t. In the next part\, I\nwill discuss the dynamical deformation of skyrmio n crystals under a\ndriving current and the corresponding suppression of t he Bragg peak\nintensities\, which we expect to be measured by neutron sca ttering\nexperiments.\n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Stefan Wessel DTSTART;TZID=Europe/Berlin:20161202T140000 DTEND;TZID=Europe/Berlin:20161202T153000 DTSTAMP:20260527T090436Z UID:0000000968@events.thp.uni-koeln.de DESCRIPTION:Stefan Wessel\, RWTH Aachen\n\nExcitation Modes and Gap Scalin g near Quantum Critical Dimerized Antiferromagnets\n\nResults are presente d from large-scale quantum Monte Carlo simulations on the excitation modes in two- \nand three-dimensional quantum antiferromagnets of coupled spin dimers accross their quantum critical \npoints. The identification of the amplitude (Higgs) mode from dynamical spin and singlet spectral \nfunction s are examined and compared to scaling predictions. For the three-dimensio nal case\, we \nidentify characteristic multiplicative logarithmic correct ions in the exciation gap scaling atop the \nleading mean-field behavior. These are in accord with field-theoretical predictions based on an \neffec tive description of the quantum critical system in terms of an asymptotica lly-free field theory. \nThe width of the Higgs mode resonance is observed to scale linearly with the Higgs mass near \ncriticality\, indicative of this critically well-defined excitation mode of the symmetry broken phase. \n\n\nContact Person: Peter Broecker LOCATION:Seminar room 0.03\, ITP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Yasir Iqbal DTSTART;TZID=Europe/Berlin:20161209T140000 DTEND;TZID=Europe/Berlin:20161209T153000 DTSTAMP:20260527T090436Z UID:0000000965@events.thp.uni-koeln.de DESCRIPTION:Yasir Iqbal\, University of Wuerzburg\n\nIntertwined nematic o rders in a frustrated ferromagnet\n\nWe investigate the quantum phases of the frustrated spin-$\\frac{1}{2}$ $J_1$-$J_2$-$J_3$ Heisenberg model on t he square lattice with ferromagnetic $J_1$ and antiferromagnetic $J_2$ and $J_3$ interactions. Using the pseudo-fermion functional renormalization g roup technique\, we find an intermediate paramagnetic phase located betwee n classically ordered ferromagnetic\, stripy antiferromagnetic\, and incom mensurate spiral phases. We observe that quantum fluctuations lead to sign ificant shifts of the spiral pitch angles compared to the classical limit. By computing the response of the system with respect to various spin rota tion and lattice symmetry-breaking perturbations\, we identify a complex i nterplay between different nematic spin states in the paramagnetic phase. While retaining time-reversal invariance\, these phases either break spin- rotation symmetry\, lattice-rotation symmetry\, or a combination of both. We therefore propose the $J_1$-$J_2$-$J_3$ Heisenberg model on the square lattice as a paradigmatic example where different intimately connected typ es of nematicities emerge in the same model.\n\nContact Person: Finn Lasse Buessen LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Karin Everschor DTSTART;TZID=Europe/Berlin:20161216T140000 DTEND;TZID=Europe/Berlin:20161216T153000 DTSTAMP:20260527T090436Z UID:0000000978@events.thp.uni-koeln.de DESCRIPTION:Karin Everschor\, University of Mainz\n\nProduction of magneti c textures via spin currents\n\nA major challenge in next-generation magne tic storage technologies is the efficient and controllable creation and ma nipulation of magnetic textures.\n\nWe predict a way to create magnetic do main walls and skyrmions by means of a homogeneous DC current without the need of specialized setups and without requiring any standard “twisting ” interactions like Dzyaloshinskii-Moriya or dipole-dipole interactions. This is possible by exploiting a dynamical instability arising by the int erplay of current-induced spin-transfer torque and locally engineered anis otropies.\n\nThe magnetic textures can be created efficiently\, controllab ly and periodically with a period that can be tuned by the applied current strength. We propose specific experimental setups to observe the periodic formation of domain walls and skyrmions.\n\n\n\nContact Person: Achim Ros ch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Yasuhiro Tada DTSTART;TZID=Europe/Berlin:20170113T140000 DTEND;TZID=Europe/Berlin:20170113T153000 DTSTAMP:20260527T090436Z UID:0000001010@events.thp.uni-koeln.de DESCRIPTION:Yasuhiro Tada\, ISSP\, Tokyo University\n\nCooper pairing in g auged fermion models for superconductivity\n\n\n\nContact Person: Achim Ro sch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Johannes Waizner DTSTART;TZID=Europe/Berlin:20170116T103000 DTEND;TZID=Europe/Berlin:20170116T120000 DTSTAMP:20260527T090436Z UID:0000001011@events.thp.uni-koeln.de DESCRIPTION:Johannes Waizner\n\nSpin wave excitations in magnetic helices and skyrmion lattices\n\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Yuval Vinkler DTSTART;TZID=Europe/Berlin:20170119T140000 DTEND;TZID=Europe/Berlin:20170119T153000 DTSTAMP:20260527T090436Z UID:0000001012@events.thp.uni-koeln.de DESCRIPTION:Yuval Vinkler\, FU Berlin\n\nTime Reversal Symmetric Topologic al Josephson Junction with a Spin Impurity\n\n\n\nContact Person: Achim R osch LOCATION:Seminar Room\, Institute for Theoretical Physics (Main Building) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Max Gerlach DTSTART;TZID=Europe/Berlin:20170120T140000 DTEND;TZID=Europe/Berlin:20170120T153000 DTSTAMP:20260527T090436Z UID:0000000990@events.thp.uni-koeln.de DESCRIPTION:Max Gerlach\n\nQuantum Monte Carlo studies of a metallic spin- density wave transition\n\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Fernando Pastawski DTSTART;TZID=Europe/Berlin:20170123T130000 DTEND;TZID=Europe/Berlin:20170123T140000 DTSTAMP:20260527T090436Z UID:0000001004@events.thp.uni-koeln.de DESCRIPTION:Fernando Pastawski\, FU Berlin\n\nHolographic quantum error co rrecting codes: geometry as a structure of information\n\n\n\nContact Pers on: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Christine Muschik DTSTART;TZID=Europe/Berlin:20170123T160000 DTEND;TZID=Europe/Berlin:20170123T170000 DTSTAMP:20260527T090436Z UID:0000001005@events.thp.uni-koeln.de DESCRIPTION:Christine Muschik\, University of Innsbruck\n\nReal-time dynam ics of lattice gauge theories with a few-qubit quantum computer\n\nGauge t heories are fundamental to our understanding of interactions between the e lementary constituents of matter as mediated by gauge bosons. However\, co mputing the real-time dynamics in gauge theories is a notorious challenge for classical computational methods. In the spirit of Feynman's vision of a quantum simulator\, this has recently stimulated theoretical effort to d evise schemes for simulating such theories on engineered quantum-mechanica l devices\, with the difficulty that gauge invariance and the associated l ocal conservation laws (Gauss laws) need to be implemented. Here we report the first experimental demonstration of a digital quantum simulation of a lattice gauge theory\, by realising 1+1-dimensional quantum electrodynami cs (Schwinger model) on a few-qubit trapped-ion quantum computer. We are i nterested in the real-time evolution of the Schwinger mechanism\, describi ng the instability of the bare vacuum due to quantum fluctuations\, which manifests itself in the spontaneous creation of electron-positron pairs. T o make efficient use of our quantum resources\, we map the original proble m to a spin model by eliminating the gauge fields in favour of exotic long -range interactions\, which have a direct and efficient implementation on an ion trap architecture. We explore the Schwinger mechanism of particle-a ntiparticle generation by monitoring the mass production and the vacuum pe rsistence amplitude. Moreover\, we track the real-time evolution of entang lement in the system\, which illustrates how particle creation and entangl ement generation are directly related. Our work represents a first step to wards quantum simulating high-energy theories with atomic physics experime nts\, the long-term vision being the extension to real-time quantum simula tions of non-Abelian lattice gauge theories. \n\n[1] E. A. Martinez*\, C. A. Muschik*\, P. Schindler\, D. Nigg\, A. Erhard\, M. Heyl\, P. Hauke\, M. Dalmonte\, T. Monz\, P. Zoller\, and R. Blatt\, Nature 534\, 516-519 (201 6).\n\nContact Person: Achim Rosch LOCATION:Seminar room\, Theoretical Physics END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Michael Kastoryano DTSTART;TZID=Europe/Berlin:20170127T140000 DTEND;TZID=Europe/Berlin:20170127T150000 DTSTAMP:20260527T090436Z UID:0000001008@events.thp.uni-koeln.de DESCRIPTION:Michael Kastoryano\, Niels Bohr International Academy\n\nNew t ools from Quantum Information Theory for the analysis of Many body systems \n\n In a celebrated recent result\, Fawzi and Renner [CMP 340 (2015)] sho wed that for a given quantum state\, and a tripatition ABC of a quantum sy stem\, the conditional mutual information I(A:C|B) is small if and only if there exists a map which approximately recovers the erasure of subsystem C\, without acting on system A. Such states are called Markov states\, and the maps are called local recovery maps. \nI will consider applications o f this important new result to the analysis of many-body systems. In parti cular\, I will show that if the thermal (Gibbs) state of a local Hamiltoni an is Markov\, and satisfies some physically reasonable assumption on the long range correlations\, then (i) expectation values of local observables can be evaluated efficiently\, and (ii) the Gibbs state can be sampled (p repared) efficiently on a quantum computer. \nUsing similar methods\, I wi ll argue that ground states of certain local gapped Hamiltonians can be pr epared in sub-linear time (on a quantum computer) if and only if the topol ogical entanglement entropy is zero. \nFurthermore\, a slight strengthenin g of these methods provide checkable conditions for the parent Hamiltonian of a PEPS to be gapped\, as long as the Li-Haldane type conjecture holds. I'll finally comment on further applications of local recovery maps\, inc luding approximate error correcting codes and toy models for the AdS/CFT c orrespondence\, and argue that these tools from quantum information theory will play an important role in analysis of many body systems. \n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Max Hering DTSTART;TZID=Europe/Berlin:20170202T123000 DTEND;TZID=Europe/Berlin:20170202T133000 DTSTAMP:20260527T090436Z UID:0000001000@events.thp.uni-koeln.de DESCRIPTION:Max Hering\, FU Berlin\n\nFunctional-renormalization-group ana lysis of Dzyaloshinsky-Moriya and Heisenberg spin interactions on the kago me lattice\n\nWe investigate the effects of Dzyaloshinsky-Moriya (DM) inte ractions on\nthe frustrated J_1-J_2 kagome-Heisenberg model using the pseu do-fermion\nfunctional-renormalization-group (PFFRG) technique. In order t o treat the\noff-diagonal nature of DM interactions\, we develop an extend ed PFFRG\nscheme. We benchmark this approach in parameter regimes that hav e\npreviously been studied with other methods and find good agreement of t he\nmagnetic phase diagram. Particularly\, finite DM interactions are foun d to\nstabilize all types of non-collinear magnetic orders of the J_1-J_2\ nHeisenberg model (q=0\, √3x√3\, and cuboc orders) and shrink the exte nts of\nmagnetically disordered phases. We discuss our results in the ligh t of the\nmineral herbertsmithite which has been experimentally predicted to host a\nquantum spin liquid at low temperatures. Our PFFRG data indicat es that\nthis material lies in close proximity to a quantum critical point . In\nparts of the experimentally relevant parameter regime for herbertsmi thite\,\nthe spin-correlation profile is found to be in good qualitative a greement\nwith recent inelastic-neutron-scattering data.\n\n\nContact Pers on: Simon Trebst LOCATION:Seminar Room (I. Physik/Astrophysics) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Shunji Matsuura DTSTART;TZID=Europe/Berlin:20170207T160000 DTEND;TZID=Europe/Berlin:20170207T170000 DTSTAMP:20260527T090436Z UID:0000001006@events.thp.uni-koeln.de DESCRIPTION:Shunji Matsuura\, Niels Bohr Institute\n\nCharged entanglement entropy in SPT and SET phases\n\nIt has been known that the topological e ntanglement entropy is a useful\norder parameter to detect topologically o rdered phases.\nWhen global symmetries are imposed\, new types of topologi cal phases emerge.\nThey are called symmetry protected topological (SPT) p hases for short range entangled states\nand symmetry enriched topological (SET) phases for long range entangled states.\nSince the entanglement ent ropy is insensitive to global symmetries\,\nthe topological entanglement e ntropy is no longer a good order parameter to distinguish\nSPT and SET pha ses.\nIn this talk I introduce a new entanglement quantity\, a charged ent anglement entropy\,\nby grand canonically generalising the entanglement en tropy.\nThis charged entanglement entropy is sensitive to global symmetrie s\,\nand it shows a new universal term\, in addition to the topological en tanglement entropy\,\nwhich can be used to distinguish SPT and SET phases. \n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Terenz Feng DTSTART;TZID=Europe/Berlin:20170210T140000 DTEND;TZID=Europe/Berlin:20170210T153000 DTSTAMP:20260527T090436Z UID:0000001009@events.thp.uni-koeln.de DESCRIPTION:Terenz Feng\n\nMoving Majorana States in 1d p-wave Superconduc tors\n\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Ciaran Hickey DTSTART;TZID=Europe/Berlin:20170302T100000 DTEND;TZID=Europe/Berlin:20170302T113000 DTSTAMP:20260527T090436Z UID:0000001027@events.thp.uni-koeln.de DESCRIPTION:Ciaran Hickey\, University of Toronto\n\nChiral Magnetic and T opological Order in Mott Insulators\n\nExperimentalists have recently been able to engineer non-trivial topological band structures using ultracold atoms in optical lattices. Motivated by ongoing experimental efforts to tu ne interactions\, we explore the interplay between strong correlations and topology in these systems. \n\nFocusing on the Haldane-Hubbard honeycomb model as an example\, we show that its strongly interacting Mott limit exh ibits various chiral magnetic orders\, including a wide regime of triple-Q tetrahedral order. Incorporating an additional third-neighbour hopping fr ustrates and ultimately melts the tetrahedral magnetic order. From analysi ng low energy spectra\, many-body Chern numbers\, entanglement spectra\, a nd modular matrices\, we identify the molten state as a chiral spin liquid with gapped semion excitations. Our numerical results suggest that this f rustration induced melting may be realised as an exotic continuous quantum phase transition. \n\nFinally\, we discuss recent results which point tow ard a common mechanism of realising chiral spin liquids in Mott insulators through the continuous melting of non-coplanar magnetic "parent" states.\ n\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Laura Baez DTSTART;TZID=Europe/Berlin:20170315T100000 DTEND;TZID=Europe/Berlin:20170315T113000 DTSTAMP:20260527T090436Z UID:0000001001@events.thp.uni-koeln.de DESCRIPTION:Laura Baez\, FU Berlin\n\nNumerical treatment of spin systems with unrestricted spin length S: A functional renormalization group study\ n\n\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Masahiko G. Yamada DTSTART;TZID=Europe/Berlin:20170316T100000 DTEND;TZID=Europe/Berlin:20170316T113000 DTSTAMP:20260527T090436Z UID:0000001035@events.thp.uni-koeln.de DESCRIPTION:Masahiko G. Yamada\n\nDesigning Kitaev spin liquids in metal-o rganic frameworks\n\n\n\nContact Person: Maria Hermanns LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Nicola Wurz DTSTART;TZID=Europe/Berlin:20170317T140000 DTEND;TZID=Europe/Berlin:20170317T153000 DTSTAMP:20260527T090436Z UID:0000001007@events.thp.uni-koeln.de DESCRIPTION:Nicola Wurz\, University of Bonn\n\nImprinting Spin Spirals i nto an Ultracold Fermi Gas\n\n\n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Jan Attig DTSTART;TZID=Europe/Berlin:20170331T140000 DTEND;TZID=Europe/Berlin:20170331T150000 DTSTAMP:20260527T090436Z UID:0000001036@events.thp.uni-koeln.de DESCRIPTION:Jan Attig\, University of Cologne\n\nClassical Spin Spirals in Frustrated Magnets from Free-Fermion Band Topology\n\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Christoph Berke DTSTART;TZID=Europe/Berlin:20170522T100000 DTEND;TZID=Europe/Berlin:20170522T113000 DTSTAMP:20260527T090436Z UID:0000001082@events.thp.uni-koeln.de DESCRIPTION:Christoph Berke\, TU Dresden\n\nWeyl semimetal on the pyrochlo re lattice\n\nThe study of topological phases of matter is among the most active research fields in modern solid state physics. Over the last couple of years\, there has been growing interest in the topological classificat ion of gapless systems. One example of a gapless system\, with defining to pological properties\, is the Weyl semimetal (TWS). In Weyl semimetals\, c onduction and valence bands touch at isolated points in the Brillouin zone . These Weyl points are topologically pro- tected and can only disappear i f they annihilate pairwise. The Weyl semimetal hosts non-trivial surface s tates\, which take the form of open Fermi arcs\, connect- ing the projecti ons of two Weyl points to the Brillouin zone of the surface. Due to the ro bustness of this phase\, Weyl semimetals are of interest for applications in quantum computers or electronic devices. In this work\, we consider a m odel for the iridium electrons in pyrochlore iridates. For this material c lass\, a Weyl- semimetal phase has been predicted. We calculate the phase diagram and find a rich variety of phases\, the TWS\, a strong topological insulator\, a type-II Weyl semimetal and various kinds of magnetic order. For the TWS\, we study the un- conventional surface states for various ge ometries. For lower electron densities\, we find a plethora of new magneti c configurations. We then turn our attention towards possible instabilitie s in Weyl semimetals. We study the stability of the Weyl semimetal phase a gainst the formation of charge density waves. In the back- folded Brilloui n zone\, Weyl points that were originally far apart can be mapped close to each other and annihilate if that reduces the free energy. However we did not find a charge density wave. We therefore study the behavior of Weyl p oints under the influence of a charge density wave. We find mechanisms\, t hat could possibly avoid the formation of such a charge configuration. For example\, one-dimensional Fermi lines emerge.\n\nContact Person: Simon Tr ebst LOCATION:Seminarraum E0.02 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Nikolai Kiselev DTSTART;TZID=Europe/Berlin:20170602T140000 DTEND;TZID=Europe/Berlin:20170602T153000 DTSTAMP:20260527T090436Z UID:0000001085@events.thp.uni-koeln.de DESCRIPTION:Nikolai Kiselev\, Peter Gruenberg Institut and Institute for A dvanced Simulation\n\n3D magnetic textures in chiral magnets\n\n\n\nContac t Person: Jan Mueller LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Mikael Fremling DTSTART;TZID=Europe/Berlin:20170616T140000 DTEND;TZID=Europe/Berlin:20170616T153000 DTSTAMP:20260527T090436Z UID:0000001073@events.thp.uni-koeln.de DESCRIPTION:Mikael Fremling\, University of Maynooth\n\nComposite Fermion Fermi liquid and the half-filled Landau level\n\n\n\nContact Person: Maria Hermanns LOCATION:0.03 ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Maximilian Genske DTSTART;TZID=Europe/Berlin:20170707T140000 DTEND;TZID=Europe/Berlin:20170707T153000 DTSTAMP:20260527T090436Z UID:0000001051@events.thp.uni-koeln.de DESCRIPTION:Maximilian Genske\n\nPhD Defense\n\n\n\nContact Person: not sp ecified LOCATION:Seminar Room 0.03 ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Chris Hooley DTSTART;TZID=Europe/Berlin:20170714T140000 DTEND;TZID=Europe/Berlin:20170714T153000 DTSTAMP:20260527T090436Z UID:0000001084@events.thp.uni-koeln.de DESCRIPTION:Chris Hooley\, University of St. Andrews\n\nFeynman path integ rals over matrix product states: insights into unconventional phase transi tions\n\nAn interesting topic in the theory of quantum phase transitions i s that of the transition between a classically ordered state\, such as a N éel state\, and a quantum ordered state\, such as a valence bond crystal. On the classically ordered side of the transition\, we have a well devel oped understanding based on the spontaneous breaking of a continuous symme try and the occurrence of associated Goldstone modes (spin waves). On the quantum ordered side\, things are rather less clear. Even the descriptio n of the quantum ordered state itself is not straightforward\, since it is not a saddle-point of the usual spin-coherent-state path integral.\n \nIn this talk\, I shall present an approach designed to address this problem by constructing the path integral over matrix product states rather than s pin coherent states. This allows both classically ordered states (which a re matrix product states of bond dimension 1) and quantum ordered states ( which are matrix product states of higher bond dimension) to be captured o n an equal footing. I shall use this approach to show that\, for at least one example of such a transition\, a Landau-Ginzburg-Wilson-type descript ion can be given\, where the ‘order parameter’ is a field representing the nearest-neighbour entanglement of the spins.\n \nThe talk is designed to be entirely self-contained: in particular\, no prior knowledge of matr ix product states or quantum ordered phases is assumed. The work about wh ich I shall speak was undertaken in collaboration with Andrew Green (Unive rsity College London)\, Jonathan Keeling (St Andrews)\, and Steve Simon (O xford)\, under the auspices of the TOPNES programme. Most of the details can be found at https://arxiv.org/abs/1607.01778.\n\nContact Person: not s pecified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Tomáš Bzdušek DTSTART;TZID=Europe/Berlin:20170721T140000 DTEND;TZID=Europe/Berlin:20170721T153000 DTSTAMP:20260527T090436Z UID:0000001087@events.thp.uni-koeln.de DESCRIPTION:Tomáš Bzdušek\, ETH Zürich\n\nBringing order to the zoo of band structure nodes\n\n\n\nContact Person: Maria Hermanns LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Kazumasa Hattori DTSTART;TZID=Europe/Berlin:20170824T140000 DTEND;TZID=Europe/Berlin:20170824T153000 DTSTAMP:20260527T090436Z UID:0000001127@events.thp.uni-koeln.de DESCRIPTION:Kazumasa Hattori\, Tokyo Metropolitan University\n\nMultiorbit al superconductors and local nodal cooper pairs\n\n\n\nContact Person: Ach im Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Falko Pientka DTSTART;TZID=Europe/Berlin:20171013T140000 DTEND;TZID=Europe/Berlin:20171013T153000 DTSTAMP:20260527T090436Z UID:0000001142@events.thp.uni-koeln.de DESCRIPTION:Falko Pientka\, Harvard University\n\nTransport phenomena of n eutral excitations in interacting 2d systems\n\nIn the first part of the t alk\, I will propose a transport experiment of \nexcitons in 2d transition -metal dichalcogenides. Due to their \ninteractions with unbound electrons in the Fermi sea\, excitons are \ndressed by a cloud of particle-hole exc itations forming Fermi polarons. \nAn in-plane electric field cannot direc tly accelerate neutral excitons\, \nhowever\, due to the polaronic dressin g\, the unbound electrons will drag \nthe excitons along. This phenomenon is similar to Coulomb drag in \nbilayer semiconductors. We determine the d rag conductivity for a low \ndensity of excitons using simple arguments as well as a diagrammatic \ncalculation based on a self-consistent T matrix approximation. Due to \nthe strong nonperturbative coupling\, the exciton drag mobility is \nexpected to be of the same order as the electron mobili ty even at zero \ntemperature.\nTime permitting\, I will discuss a novel p robe of quantum Hall \nferromagnetism in graphene based on thermal transpo rt in the second part \nof the talk. Strong interactions lift the high deg eneracy of the \nzero-energy Landau level in graphene mono- and bilayers\, giving rise to \na rich phase diagram of competing spin and valley order. Here we show \nthat thermal transport at low temperatures can give compel ling evidence \nfor spontaneous symmetry breaking and exhibits many other signatures \ndistinguishing the various phases.\n\nContact Person: not spe cified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Lukas Janssen DTSTART;TZID=Europe/Berlin:20171020T140000 DTEND;TZID=Europe/Berlin:20171020T153000 DTSTAMP:20260527T090436Z UID:0000001132@events.thp.uni-koeln.de DESCRIPTION:Lukas Janssen\n\nA fermionic gauge theory for bosonic deconfin ed criticality\n\n\n\nContact Person: Michael Scherer LOCATION:Seminar Room 003\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Masahiko Yamada DTSTART;TZID=Europe/Berlin:20171027T140000 DTEND;TZID=Europe/Berlin:20171027T153000 DTSTAMP:20260527T090436Z UID:0000001121@events.thp.uni-koeln.de DESCRIPTION:Masahiko Yamada\, ISSP\, University of Tokyo\n\nCrystalline sp in-orbital liquids with an emergent SU(4) symmetry\n\nA promising approach to realize quantum spin liquids is to enhance\nthe spin-space symmetry fr om usual SU(2) to SU(N). While the SU(N)\nsymmetry with a general N is pro posed in ultracold atoms using\nnuclear spin degrees of freedom\, its real ization in magnetic\nmaterials is challenging. Here we propose a new mecha nism by\nwhich the SU(4) symmetry emerges in the strong spin-orbit couplin g\nlimit. The spin-orbit coupling in d^1 transition metal compounds\nwith edge-sharing anion octahedra leads to strongly\nbond-dependent hopping\, w hich is apparently not SU(4)-symmetric.\nHowever\, in the honeycomb struct ure\, a gauge transformation maps\nthe system to an SU(4)-symmetric Hubbar d model. In the strong\nrepulsion limit at quarter filling\, the low-energ y effective model\nis the SU(4) Heisenberg model on the honeycomb lattice\ , which\ncannot have a trivial gapped ground state and is expected to\nhos t a gapless spin-orbital liquid. By generalizing this model\nto other thre e-dimensional lattices\, we also propose crystalline\nspin-orbital liquids protected by this emergent SU(4) symmetry\nand space group symmetries.\n\ nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Joaquin E. Drut DTSTART;TZID=Europe/Berlin:20171103T140000 DTEND;TZID=Europe/Berlin:20171103T153000 DTSTAMP:20260527T090436Z UID:0000001115@events.thp.uni-koeln.de DESCRIPTION:Joaquin E. Drut\, University of North Carolina\n\nSignal-to-no ise issues in non-relativistic matter: from entanglement to thermodynamics \n\nNon-relativistic quantum matter\, as realized in ultracold atomic gase s\, continues to be a remarkably versatile playground for many-body physic s. Experimentalists have exquisite control over temperature\, density\, co upling\, and shape of the trapping potential. Additionally\, a wide range of properties can be measured: from simple ones like equations of state to more involved ones like the bulk viscosity and entanglement. The latter h as received much attention due to its connection to quantum phase transiti ons\, but it has proven extremely difficult to compute: stochastic methods display exponential signal-to-noise issues of a very similar nature as th ose due to the infamous sign problem affecting finite-density QCD. In this talk\, I will present an algorithm that solves the signal-to-noise issue for entanglement\, and I will show results for strongly interacting system s in three spatial dimensions that are the first of their kind. I will als o present a few recent explorations of the thermodynamics of polarized mat ter and other cases that usually have a sign problem\, using complexified stochastic quantization.\n\nContact Person: Zala Lenarcic LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Ipsita Mandal DTSTART;TZID=Europe/Berlin:20171116T140000 DTEND;TZID=Europe/Berlin:20171116T150000 DTSTAMP:20260527T090436Z UID:0000001178@events.thp.uni-koeln.de DESCRIPTION:Ipsita Mandal\, MPI-PKS Dresden\n\nCritical Fermi Surface: UV/ IR mixing and Superconducting Instability\n\nWe discuss the perturbative c ontrol of low-energy effective theory of strongly-interacting systems whic h cannot be treated within the Landau Fermi liquid framework. These are ge nerically called non-Fermi liquids where quasiparticles do not exist. In p articular\, we focus on critical Fermi surface states where there is a wel l-defined Fermi surface\, but no quasiparticle resulting from the strong i nteraction between the\nFermi surface and a massless boson. We will show t hat for Fermi surface having a dimension m>1\, the Fermi momentum k_F ente rs the expressions for physical quantities as a dimensionful parameter lea ding to UV/IR mixing\, thus modifying the naive scaling arguments\, wherea s for a one-dimensional Fermi surface there is an emergent locality with n o such k_F dependence.\n\nContact Person: Alex Altland LOCATION:Seminarraum Altbau Theorie END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Lukas Sieberer DTSTART;TZID=Europe/Berlin:20171117T140000 DTEND;TZID=Europe/Berlin:20171117T153000 DTSTAMP:20260527T090436Z UID:0000001161@events.thp.uni-koeln.de DESCRIPTION:Lukas Sieberer\, University of Innsbruck\n\nDesigning quantum paths in adiabatic quantum computing\n\nThe computational superiority of a computer that operates according to the laws\nof quantum mechanics relies crucially on quantum parallelism: different sets of\ndata stored as a sup erposition of quantum states can be processed in\nparallel. To play out th is advantage\, however\, one has to be able to prepare\nsuch superposition s in the first place --- using only a minimum of computational\nresources. We present a framework to efficiently prepare superpositions of\nmany-bod y spin configurations with programmable squared amplitudes. The spin\nconf igurations are encoded in the degenerate ground states of the lattice-gaug e\nrepresentation of an all-to-all connected Ising spin glass. The ground state\nmanifold is invariant under variations of the gauge degrees of free dom\, which\ntake the form of four-body parity constraints. Our framework makes use of these\ndegrees of freedom by individually tuning them to dyna mically prepare\nprogrammable superpositions. The dynamics combines an adi abatic protocol with\ncontrolled diabatic transitions.\n\nContact Person: Sebastian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Frank Schindler DTSTART;TZID=Europe/Berlin:20171128T140000 DTEND;TZID=Europe/Berlin:20171128T153000 DTSTAMP:20260527T090436Z UID:0000001163@events.thp.uni-koeln.de DESCRIPTION:Frank Schindler\, University of Zurich\n\nHigher-order topolec trical circuits\n\nHigher-order topological insulators have been recently proposed as unprecedented quantum states of matter. In two spatial dimensi ons\, they incorporate quantized electric quadrupole insulators\, which fe ature zero-dimensional topological corner midgap states. These states are protected by the bulk gap\, reflection symmetries\, and a spectral symmetr y\, while their edges are gapped. Although such novel topological phases a re often hard to come by in real materials\, there are various analogue pl atforms that enable us to realize the corresponding band theory concepts i n classical systems. I will talk about how we developed and measured a top olectrical circuit design for a quadrupole insulator\, the midgap states o f which manifest themselves as topological boundary resonances in the corn er impedance profile of the circuit. This establishes an instance where to polectrical circuitry is employed to bridge the gap between quantum theore tical modeling and the experimental realization of topological band struct ures.\n\nContact Person: Finn Lasse Buessen LOCATION:Seminarraum Kernphysik END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Tobias Meng DTSTART;TZID=Europe/Berlin:20171201T140000 DTEND;TZID=Europe/Berlin:20171201T153000 DTSTAMP:20260527T090436Z UID:0000001138@events.thp.uni-koeln.de DESCRIPTION:Tobias Meng\, TU Dresden\n\nThe gravity of Weyl: tabletop sign atures of the mixed axial-gravitational anomaly\n\nTopological semimetals have recently been one of the most active topics in solid state physics\, and provide an exceptionally fruitful meeting point for fields as diverse as chemistry\, band structure calculations and high-energy field theory. T his talk will discuss the observation of quantum anomalies in Weyl semimet als. These anomalies are rooted in an incompatibility of quantum mechanics and classical conservation laws. In particular\, I will focus on recent m easurements demonstrating the presence of the mixed axial-gravitational an omaly in Weyl semimetals. In contrast to earlier expectations\, which woul d for example search for this phenomenon in the hydrodynamics of neutron s tars\, we used a conceptually simple thermoelectric transport experiment t o find signatures of the mixed axial-gravitational anomaly in the Weyl sem imetal NbP.\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Adam Smith DTSTART;TZID=Europe/Berlin:20171207T140000 DTEND;TZID=Europe/Berlin:20171207T153000 DTSTAMP:20260527T090436Z UID:0000001185@events.thp.uni-koeln.de DESCRIPTION:Adam Smith\, University of Cambridge\n\nDisorder-Free Localiza tion\n\n\n\nContact Person: Achim Rosch LOCATION:Seminarraum Alte Theorie END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Gabor Halasz DTSTART;TZID=Europe/Berlin:20171213T100000 DTEND;TZID=Europe/Berlin:20171213T113000 DTSTAMP:20260527T090436Z UID:0000001153@events.thp.uni-koeln.de DESCRIPTION:Gabor Halasz\, KITP\n\nParton constructions and realistic spin models of fracton topological orders\n\nFracton phases are gapped quantum phases in three dimensions that go beyond the standard paradigm of topolo gical order\; they have fractionalized excitations that are immobile or on ly mobile along lower-dimensional subsystems\, such as lines or planes. Wh ile there are several exactly solvable models of such fracton phases\, the se models are far from realistic because they involve interactions between many spins at the same time. By generalizing the fermionic parton constru ction\, a standard phenomenological description of fractionalization in qu antum phases\, we provide simple variational states capturing fracton phas es. Moreover\, by showing that each variational state is the asymptotic st rong-coupling ground state of a corresponding coupled-spin-chain model\, w e demonstrate that a large class of fracton phases can be realized in more realistic models involving only two-spin interactions.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Yuta Murakami DTSTART;TZID=Europe/Berlin:20171215T140000 DTEND;TZID=Europe/Berlin:20171215T153000 DTSTAMP:20260527T090436Z UID:0000001158@events.thp.uni-koeln.de DESCRIPTION:Yuta Murakami\, University of Fribourg\n\nPeriodic driving of correlated systems: high-harmonic generation in the Mott insulator and par ametric phonon excitation in superconductors\n\nDriving systems out of equ ilibrium can provide new ways to control properties and extract new functi ons.\nRecent development of intense laser in a wide frequency range has le d to intriguing observations \nsuch as light-induced superconductivity-lik e behaviors above the transition temperature [1]\,\nenhancement of the exc itonic condensation [2] and high-harmonic generation in solid states [3].\ n\nMotivated by this intriguing situation\, we have been developing noneq uilibrium methods based on the dynamical mean-field theory (DMFT). \nHere we would like to present recent two applications of the nonequilibrium DMF T for the time-periodic steady states (Floquet DMFT).\n\nIn the first part \, we discuss the high-harmonic generation (HHG) in the Mott insulator und er periodic AC driving [4]. \nWe show that qualitative behavior of the HHG spectrum is different between weak and strong field regimes\,\nwhich orig inates from qualitative difference in doublon/holon dynamics under the dri ving. \nWe also discuss the similarity and the difference of the HHG inten sity in the Mott insulator compared to that of semiconductors and disorder ed systems.\n\nIn the second part\, we discuss the effects of the parametr ic-phonon driving on conventional SC\, which has been considered to enhanc e SC[5][6]. \nBy studying transient dynamics and steady states\, we demons trate that even though the attractive interaction can be enhanced by the d riving\, \nSC is always suppressed\, in particular\, at the parametric res onance. Our systematic analysis shows that\, in a wide parameter range\, \ nthe heating of the system is the dominant effect and the parametric phono n driving has a negative effect on SC.\n\n[1] M. Mitrano et al.\, Nature 5 30\, 461 (2016).\n[2] S. Mor et al.\, PRL 119\, 086401 (2017).\n[3] S. Ghi mire et al.\, Nat. Phys. 7\, 138 (2011).\n[4] Y. Murakami\, M. Eckstein\, P. Werner to be published.\n[5] M. Knap et al.\, PRB 94\, 214504 (2016)\; M. Babadi et al.\, PRB 96\, 014512 (2017).\n[6] Y. Murakami et al\, PRB 96 \, 045125 (2017).\n\nContact Person: Zala Lenarcic LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Pieter Naaijkens DTSTART;TZID=Europe/Berlin:20171218T140000 DTEND;TZID=Europe/Berlin:20171218T150000 DTSTAMP:20260527T090436Z UID:0000001189@events.thp.uni-koeln.de DESCRIPTION:Pieter Naaijkens\, RWTH Aachen\n\nThe mathematics of topologic ally ordered phases\n\nOne of the most interesting properties of topologic ally ordered models with\nlong ranged entanglement\, such as Kitaev's tori c code\, is that they have\nanyonic excitations. The properties of these a nyons can be recovered from\nfirst principles using techniques from mathem atical physics\, making it\npossible to put conjectures about such systems in a precise mathematical\nlanguage. After explaining the main ideas behi nd this construction\, I will\ndiscuss recent results on the stability of the excitation structure and on\napplications to quantum information theor y.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Christian Gogolin DTSTART;TZID=Europe/Berlin:20171218T160000 DTEND;TZID=Europe/Berlin:20171218T170000 DTSTAMP:20260527T090436Z UID:0000001190@events.thp.uni-koeln.de DESCRIPTION:Christian Gogolin\, ICFO Barcelona\n\nPure state quantum stati stical mechanics - an overview\n\nIn this talk I will given an overview of pure state quantum statistical mechanics\, which is a new way of understa nding issues at the foundation of statistical mechanics and thermodynamics . In particular\, I will explain recent developments concerning equilibrat ion and thermalization in closed quantum many-body systems. We will see ho w equilibration and thermalization can be defined in unitarily evolving an d finite dimensional quantum systems\, under which conditions they can be proved to happen\, and what we know about the apparent equilibrium states. I will further speak about general results on structural properties both short- and long-range interacting many-body systems\, with a focus on the decay of correlations in their thermal states. Finally\, I will provide a glimpse of ongoing work concerning the use of machine learning tools form many-body physics and point out opportunities for future work.\n\n\nContac t Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Leonardo Mazza DTSTART;TZID=Europe/Berlin:20171221T160000 DTEND;TZID=Europe/Berlin:20171221T170000 DTSTAMP:20260527T090436Z UID:0000001188@events.thp.uni-koeln.de DESCRIPTION:Leonardo Mazza\, ENS Paris\n\nMajorana fermions in particle-co nserving settings\n\nThe paradigmatic condensed-matter models where zero-e nergy localized Majorana fermions have been studied so far have the distin guishing feature of not conserving the number of fermions. Moreover\, the accepted definition of "Majorana fermion" naturally belongs to this scenar io. Is it possible to discuss Majorana fermions in "canonical" particle-co nserving settings?\n\nIn this seminar I will present several exact and num erical results on Majorana fermions in particle-conserving scenarios. I wi ll start from the discussion of a model for bosons and fermions where\, in a proper limit\, the physics of the celebrated Kitaev's chain appears. I will continue by presenting exact results on Majorana fermions in ladder m odels where the two legs of the system can only exchange pair of particles . Finally\, I will comment on the possibility of making experiments with M ajorana fermions in particle-conserving settings using cold atoms.\n\n\nCo ntact Person: Simon Trebst LOCATION:Seminarraum E0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Aris Alexandradinata DTSTART;TZID=Europe/Berlin:20171222T150000 DTEND;TZID=Europe/Berlin:20171222T160000 DTSTAMP:20260527T090436Z UID:0000001187@events.thp.uni-koeln.de DESCRIPTION:Aris Alexandradinata\, Yale\n\nUnveiling the hidden topology i n the Fermi-surface wavefunction of metals\n\nA metal is a solid with a Fe rmi surface. It is known how to reconstruct the shape of the Fermi surface – by immersing the metal in a magnetic field and measuring the period o f field-induced oscillations of the magnetization/resistivity. I will show how to extract information about the quantum-mechanical wavefunction of t he Fermi surface – from measuring the phase offset of these same oscilla tions. In some metals\, this information is robust against deformations of the Hamiltonian (describing the metal)\, and may therefore be viewed as a topological invariant.\n\n\nContact Person: Simon Trebst LOCATION:Seminarraum E0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Carolin Wille DTSTART;TZID=Europe/Berlin:20180112T140000 DTEND;TZID=Europe/Berlin:20180112T150000 DTSTAMP:20260527T090436Z UID:0000001193@events.thp.uni-koeln.de DESCRIPTION:Carolin Wille\, FU Berlin\n\nA tensor network approach to topo logical quantum phases\n\nTensor network states\, and in particular projec ted entangled pair\nstates\, play an important role in the description of strongly correlated\nquantum lattice systems. They do not only serve as va riational states in\nnumerical simulation methods\, but also provide a fra mework for\nclassifying phases of quantum matter and capture notions of to pological\norder in a stringent and rigorous language. In this talk I will present\nhow virtual symmetries in tensor networks\, summarized by the fr amework\nof matrix product operator (MPO) injectivity\, are substantial to the\nclassification of not only bosonic but also fermionic topological or der\nin two dimensional systems. I will briefly discuss how this fact rela tes\nto Levin-Wen string net models and Tuarev-Viro state sum construction s.\nFor the sake of concreteness\, two examples of fermionic topological\n order\, the fermionic toric code and the Majorana dimer model\, are\ndiscu ssed using the language of fermionic tensor networks.\n\n\nContact Person: Alex Altland LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Enej Ilievski DTSTART;TZID=Europe/Berlin:20180119T140000 DTEND;TZID=Europe/Berlin:20180119T153000 DTSTAMP:20260527T090436Z UID:0000001196@events.thp.uni-koeln.de DESCRIPTION:Enej Ilievski\, University of Amsterdam\n\nHydrodynamic equati on for thermodynamic classical and quantum soliton gases\n\nExactly solvab le nonlinear wave equations -- colloquially known as the soliton systems - - are widely regarded as one of the greatest achievements of mathematical physics. But somehow\, aside of several mathematical frameworks and other formal aspects\, not a lot seems to be known about statistical properties of classical integrable field theories and\, in particular\, classical tra nsport properties at finite temperature. In this talk\, we present a kinet ic equation to deal with dense soliton gases\, expressed in terms of a lin ear integral dressing equation for the soliton spectral function which acc ounts for renormalization of the soliton velocities due to the interaction s with a soliton many-body state. This is accomplished in the framework of the algebro-geometric integration technique which permits to classify all quasi-periodic solutions of an integrable equation of motion in terms of the moduli of finite-genus Riemann surfaces. By identifying soliton excita tions\, applying Born-Sommerfeld quantization for soliton orbits\, extract ing the two-body S-matrix\, and finally taking the thermodynamic finite-de nsity\, the free energy functional is expressed as the saddle point of the action-space path-integral. Our hydrodynamic equations can understood as the thermodynamic analogue of the celebrated Whitham's modulation equation s. The equations are universal\, and even apply to the quantum theories of solitons. If time permits\, we show how to obtain a closed compact formul a for the Drude weight in the quantum Heisenberg spin chain\, and discuss peculiarities related to it.\n\nContact Person: Zala Lenarcic LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Denis Golez DTSTART;TZID=Europe/Berlin:20180126T140000 DTEND;TZID=Europe/Berlin:20180126T153000 DTSTAMP:20260527T090436Z UID:0000001197@events.thp.uni-koeln.de DESCRIPTION:Denis Golez\, University of Fribourg \n\nRelaxation dynamics i n Mott insulators: the role of collective modes\n\nStrong correlations bet ween spin\, charge and orbital degrees of freedom play an important role i n materials and a recent development of ultrafast spectroscopies enabled t o disentangle these relevant degrees of freedom by their temporal evolutio n.\nI will start with a summary of the charge carrier relaxation after the photo-excitation in Mott insulators described within the dynamical mean f ield theory (DMFT) and continue how this formalism can be extended to incl uding the role of dynamical screening and non-local fluctuations (GW+EDFMT )[1\,2]. Then I will open the question how to use the laser pulse to manip ulate screening in Mott insulators. As an extreme example I will present a self-trapping of the system in the negative temperature state by a proper manipulation of the screening environment\, which leads to the enhanced s ubgap response in the charge susceptibility. This population inversion lea ds to the low-energy anti-screening and I will comment on its experimental relevance. In the second part I will shed light on the role of spin fluct uations in the relaxation dynamics\, which can be analysed by an extension of DMFT[3]. I will exemplify how optical pump probe techniques can be use d to detect some basic theoretical ideas in higher dimensional doped antif erromagnets\, like string states\, Trugman paths and the lack of spin-char ge separation. At the end I will provide an outlook how to extend these to ols to an ab-initio description of strongly correlated materials out of eq uilibrium.\n\n[1] D. Golez\, M. Eckstein\, and P. Werner. Phys. Rev. B\, 9 2:195123\, Nov (2015).\n[2] D. Golez\, L. Boehnke\, H. U. R. Strand\, M. E ckstein\, and P. Werner. Phys. Rev. Lett. 118:246402 (2017).\n[3] N. Bittn er\, D. Golez\, M. Eckstein\, P. Werner\, in preparation.\n\nContact Perso n: Zala Lenarcic LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Bjoern Ladewig DTSTART;TZID=Europe/Berlin:20180202T140000 DTEND;TZID=Europe/Berlin:20180202T153000 DTSTAMP:20260527T090436Z UID:0000001202@events.thp.uni-koeln.de DESCRIPTION:Bjoern Ladewig\n\nNon-equilibrium Phase Transitions in the pre sence of fluctuation less States (Master colloquium)\n\n\n\nContact Person : not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Jan Mueller DTSTART;TZID=Europe/Berlin:20180226T140000 DTEND;TZID=Europe/Berlin:20180226T153000 DTSTAMP:20260527T090436Z UID:0000001198@events.thp.uni-koeln.de DESCRIPTION:Jan Mueller\n\nMagnetic Skyrmions and Topological Domain Walls (PhD Defense)\n\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Eddy Ardonne DTSTART;TZID=Europe/Berlin:20180228T100000 DTEND;TZID=Europe/Berlin:20180228T113000 DTSTAMP:20260527T090436Z UID:0000001199@events.thp.uni-koeln.de DESCRIPTION:Eddy Ardonne\, Stockholm University\n\nExact (ground) states a nd zero-modes of interacting Spin and Clock models\n\nIn this blackboard t alk\, I will first review the old results of Peschel en Emery\, who devise d a\nset of interacting spin-1/2 models\, for which the degenerate ground states can be\nwritten in terms of product states. This model has more int eresting properties\, such\nas excited states that can be constructed expl icitly\, and one can find exact\, local\noperators that swap the ground st ates. These results can be generalized to three\nstate Clock models\, and models with arbitrary spin. If time allows\, I will comment\non how to ada pt the construction to arbitrary lattices.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Nina del Ser DTSTART;TZID=Europe/Berlin:20180404T100000 DTEND;TZID=Europe/Berlin:20180404T113000 DTSTAMP:20260527T090436Z UID:0000001232@events.thp.uni-koeln.de DESCRIPTION:Nina del Ser\, Cambrige\n\nCalculating experimental signatures of Majorana fermions in the Kitaev model\n\n\n\nContact Person: Achim Ros ch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Constantin Schrade DTSTART;TZID=Europe/Berlin:20180409T160000 DTEND;TZID=Europe/Berlin:20180409T170000 DTSTAMP:20260527T090436Z UID:0000001230@events.thp.uni-koeln.de DESCRIPTION:Constantin Schrade\, MIT\n\nMajorana Superconducting Qubits\n\ nTopological superconductors hosting spatially well-separated Majorana bou nd states offer the possibility for realizing robust qubits protected from local environmental perturbations. Revealing new properties of Majorana b ound states as well as establishing an experimentally feasible platform fo r Majorana-based quantum computing constitute two of the most urgent chall enges in the field. In this talk\, I will address these issues by discussi ng two setups of topological superconductors coupled to conventional super conductors:\n\n(1) The first setup comprises a Coulomb-blockaded time-reve rsal invariant topological superconductor island with Majorana Kramers pai rs placed in an s-wave superconductor Josephson junction. I will discuss a 2Pi Josephson effect which is mediated by the Majorana Kramers pairs and whose direction is controlled by the joint parity of all four Majorana bou nd states on the island\, a "Parity-controlled 2Pi Josephson effect". \n\n (2) The second setup constitutes a Majorana-based qubit in an all-supercon ducting circuit\, a "Majorana Superconducting Qubit". I will demonstrate h ow universal quantum computation can be achieved in such a device and disc uss advantages over conventional superconducting qubits. \n\n[1] C. Schrad e and L. Fu\, Parity-controlled 2Pi Josephson effect mediated by Majorana Kramers pairs\, arXiv:1801.03511\n[2] C. Schrade and L. Fu\, Majorana Supe rconducting Qubit\, arXiv:1803.01002\n\nContact Person: Alex Altland LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Andreas Laeuchli DTSTART;TZID=Europe/Berlin:20180416T143000 DTEND;TZID=Europe/Berlin:20180416T153000 DTSTAMP:20260527T090436Z UID:0000001228@events.thp.uni-koeln.de DESCRIPTION:Andreas Laeuchli\, University of Innsbruck\n\nComputational Sp ectroscopy of Quantum Field Theories\n\nQuantum field theories play an imp ortant role in many condensed matter systems for their description at low energies and long length scales. In 1+1 dimensional critical systems the e nergy spectrum and the spectrum of scaling dimensions are intimately relat ed in the presence of conformal symmetry. In higher space-time dimensions this relation is more subtle and not well explored numerically. In this ta lk we motivate and review our recent effort to characterize 2+1 dimensiona l quantum field theories using computational techniques 2+targeting the en ergy spectrum on a spatial torus. We discuss several examples ranging from the O(N) Wilson Fisher theories and Gross-Neveu-Yukawa theories to deconf inement- confinement transitions in the context of topological ordered sys tems. We advocate a phenomenological picture that provides insight into th e operator content of the critical field theories.\n\n\nContact Person: Si mon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Peter Broecker DTSTART;TZID=Europe/Berlin:20180416T114500 DTEND;TZID=Europe/Berlin:20180416T131500 DTSTAMP:20260527T090436Z UID:0000001231@events.thp.uni-koeln.de DESCRIPTION:Peter Broecker\n\nDisentangling and machine learning the many- fermion problem (PhD defense)\n\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Johannes Reuther DTSTART;TZID=Europe/Berlin:20180504T140000 DTEND;TZID=Europe/Berlin:20180504T153000 DTSTAMP:20260527T090436Z UID:0000001247@events.thp.uni-koeln.de DESCRIPTION:Johannes Reuther\, FU Berlin\n\nSpinon band structures in quan tum spin liquids from functional renormalization\n\nWe develop a numerical technique based on the pseudofermion functional\nrenormalization group (P FFRG) to calculate hopping and pairing amplitudes\nof emergent spinon quas iparticles in spin-1/2 quantum spin liquids. Within\nthis approach\, we fi rst formulate a self-consistent Fock-like equation for\nthese amplitudes w here instead of the bare propagators and couplings we\nuse the fully renor malized ones from PFFRG. We solve these equations using\ndifferent ansätz e for the hoppings and pairings which we take from a\nprojective symmetry group (PSG) classification. From the overall size of\nthese amplitudes we identify which of the PSGs are preferably realized in\nthe system. We appl y this approach to the antiferromagnetic J1-J2\nHeisenberg model on the sq uare lattice and to the antiferromagnetic\nnearest neighbor Heisenberg mod el on the kagome lattice. For the J1-J2\nmodel\, we find that in the regim e of maximal frustration (J1~J2/2) the\nlargest amplitudes are obtained fo r a U(1) pi-flux state with a Dirac cone\nspinon dispersion. In the case o f the kagome model we identify a gapless\nZ2 pi-flux state where the bands show a Dirac-cone-like structure at\nfinite energies but also feature a s mall circular Fermi surface at zero\nenergy. We discuss our findings and b enchmark them against variational\nMonte Carlo results.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Laura Baez DTSTART;TZID=Europe/Berlin:20180517T133000 DTEND;TZID=Europe/Berlin:20180517T143000 DTSTAMP:20260527T090436Z UID:0000001277@events.thp.uni-koeln.de DESCRIPTION:Laura Baez\, FU Berlin\n\nSearching for the minimal model of A -Li2IrO3 or: How I Learnt to Stop Worrying and love free boundary conditi ons.\n\nIn recent years\, a lot of effort has been devoted to the quest fo r experimental realizations of Kitaev interactions in spin systems. Recent ly\, many materials have been proposed which seem to realize extended Kita ev models\, where the Kitaev interactions are supplemented by Heisenberg a nd other bond dependent terms. The symmetry and electronic structure of th ese materials renders the determination of a minimal model a non trivial p ursuit. In this talk I will concentrate on one of these particular materia ls\, A-Li2IrO3\, for which various minimal models have been proposed. Empl oying large scale Monte Carlo simulations I will show how the number of pr ospective models can be reduced. I will show that many of those models do not reproduce the most recent experimental results. Furthermore\, I will p ropose and predict the results of an experiment which could help determine which one of the proposed models\, if any\, is the minimal model of A-Li2 IrO3.\n\nContact Person: Simon Trebst LOCATION:Seminarraum Alte Theorie END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Elio Koenig DTSTART;TZID=Europe/Berlin:20180518T140000 DTEND;TZID=Europe/Berlin:20180518T153000 DTSTAMP:20260527T090436Z UID:0000001216@events.thp.uni-koeln.de DESCRIPTION:Elio Koenig\n\nQuantum field theory of nematic transitions in spin orbit coupled spin-1 polar bosons\n\nWe theoretically study an ultra- cold gas of spin-1 polar bosons in one spatial dimension which are subject to a quadratic Zeeman field and a Raman induced spin-orbit coupling. Conc entrating on the regime in which the background fields can be treated pert urbatively we analytically solve the model in its low-energy sector\, i.e. we characterize the relevant phases and the quantum phase transitions bet ween them. Depending on the sign of the effective quadratic Zeeman field e psilon\, two superfluid phases with distinct nematic order appear. In addi tion\, we uncover a spin-disordered superfluid phase at strong coupling. W e employ a combination of renormalization group calculations and duality t ransformations to access the nature of the phase transitions. At epsilon=0 \, a line of spin-charge separated pairs of Luttinger liquids divides the two nematic phases and the transition to the spin disordered state at stro ng coupling is of the Berezinskii-Kosterlitz-Thouless type. In contrast\, at epsilon not equal to 0\, the quantum critical theory separating nematic and strong coupling spin disordered phases contains a Luttinger liquid in the charge sector that is coupled to a Majorana fermion in the spin secto r (i.e. the critical theory at finite epsilon maps to a quantum critical I sing model that is coupled to the charge Luttinger liquid). Due to an emer gent Lorentz symmetry\, both have the same\, logarithmically diverging vel ocity. We discuss the experimental signatures of our findings that are rel evant to ongoing experiments in ultra-cold atomic gases of 23Na. \n\nCont act Person: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Laura Classen DTSTART;TZID=Europe/Berlin:20180601T140000 DTEND;TZID=Europe/Berlin:20180601T150000 DTSTAMP:20260527T090436Z UID:0000001274@events.thp.uni-koeln.de DESCRIPTION:Laura Classen\, BNL\n\nNon-Fermi liquid behavior from quantum critical local moments\n\nWe study the temperature dependence of the elect rical resistivity in a system composed of critical spin chains interacting with three dimensional conduction electrons and driven to criticality via an external magnetic field. The relevant experimental system is Yb2Pt2Pb\ , a metal where itinerant electrons coexist with localized moments of Yb-i ons which can be described in terms of effective S=1/2 spins with dominant ly one-dimensional exchange interaction. The spin subsystem becomes critic al in a relatively weak magnetic field\, where it behaves like a Luttinger liquid. We theoretically examine a Kondo lattice with different effective space dimensionalities of the two interacting subsystems. We characterize the corresponding non-Fermi liquid behavior due to the ``local criticalit y'' from the spins by calculating the electronic relaxation rate and the d c resistivity and establish its quasi linear temperature dependence.\n\nCo ntact Person: Michael Scherer LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Alexander Seidel DTSTART;TZID=Europe/Berlin:20180608T140000 DTEND;TZID=Europe/Berlin:20180608T153000 DTSTAMP:20260527T090436Z UID:0000001219@events.thp.uni-koeln.de DESCRIPTION:Alexander Seidel\, Washington University in Saint Louis\n\nEnt angled Pauli Principles: The DNA of fractional quantum Hall fluids\n\nA ma jor challenge in the study of strongly correlated electron systems is to e stablish a firm link between microscopic models and effective field theory . Quite often\, this step involves a leap of faith\, and/or extensive nume rical studies. For fractional quantum Hall model wave functions\, there ex ists - in some cases - a scheme to infer the long distance physics of the state that is both compelling and simple\, and leaves very little room for ambiguity. This scheme involves a local parent Hamiltonian for the state\ , which unambiguously defines a "zero mode space" of elementary excitation s\, and what’s known as a "generalized Pauli principle"\, which efficie ntly organizes the zero mode space through one-dimensional patterns satisf ying local rules.\nWhere this works\, universal properties of the state un ambiguously emerge from counting exercises in terms of these patterns\, wh ich efficiently encode degeneracies\, quasi-particle types and charges\, a nd which completely determine an edge conformal field theory. There is eve n a natural scheme to infer braiding statistics directly\, for both Abelia n and non-Abelian states. Unfortunately\, such a framework thus far exist s for some quantum Hall states but not for others. In this talk\, I will r eview the state of the art of this formalism\, give reasons of why its "pl ain vanilla form" is insufficient to describe some important fractional qu antum Hall states (e.g.\, Jain states)\, \nand explain how to address this deficiency through a new\, more general concept\, called "entangled Pauli principles". It will turn out that for some interesting quantum Hall sta tes\, the efficient description advertised here involves simple matrix-pro duct-type entanglement. \n\n[1] arXiv:1803.00975\n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Kirill Shtengel DTSTART;TZID=Europe/Berlin:20180615T140000 DTEND;TZID=Europe/Berlin:20180615T150000 DTSTAMP:20260527T090436Z UID:0000001264@events.thp.uni-koeln.de DESCRIPTION:Kirill Shtengel\, UC Riverside\n\nA Fractional Chiral Semimeta l\n\nFormulating consistent theories describing strongly correlated\nmetal lic topological phases is an outstanding problem in\ncondensed-matter phys ics. I will present an explicit construction of a\nfractionalized analog o f the Weyl semimetal state: the fractional\nchiral metal. Our approach is to construct a 4+1D quantum Hall\ninsulator by stacking 3+1D Weyl semimeta ls in a magnetic field. In a\nstrong enough field\, the low-energy physics is determined by the\nlowest Landau level of each Weyl semimetal\, which is highly degenerate\nand chiral\, motivating us to use a coupled-wire app roach. In the\npresence of electron-electron interactions a gapped phase e merges\; its\nelectromagnetic response is given in terms of a Chern-Simons field\ntheory. A boundary of this four dimensional phase remains gapless. The\nboundary's response to an external electromagnetic field is determin ed\nby a chiral anomaly with a fractional coefficient. We suggest that\nsu ch an anomalous response can be taken as a working definition of a\nfracti onalized strongly correlated analog of the Weyl semimetal state.\n\nContac t Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Michael Lawler DTSTART;TZID=Europe/Berlin:20180622T140000 DTEND;TZID=Europe/Berlin:20180622T150000 DTSTAMP:20260527T090436Z UID:0000001227@events.thp.uni-koeln.de DESCRIPTION:Michael Lawler\, Cornell\n\nHow to fold a distorted kagome ant iferromagnet\n\nKagome antiferromagnets display a host of exotic magnetic phenomena originating from a massive degeneracy of classical ground states . Presumably\, this massive degeneracy is an accident and so the community 's focus has been to discover ideal kagome antiferromagnets where it is pr esent and study their properties. I will argue it is not an accident and t hat locality and\, for example\, a mirror symmetry are enough to guarantee frustration. In the process\, I will uncover a rich theory of distorted k agome antiferromagnets\, showing their ground states map onto triangulated surfaces with (origami) or without (kirigami) holes. I will show the exch ange constants J_ij behave like a background gauge field whose geometry ca n determine some of the zero modes. From a different perspective\, I will further show there are zero modes in the spin wave spectra determined by a topological classification of Maxwell counting by extending the 10-fold w ay classification of Hermitian matrices that underpin topological insulato rs to non-Hermitian matrices. I will conclude by applying the theory to tw o materials and demonstrate explicitly the existence of either flat bands (Cs_2ZrCu_3F_{12}) and line-degeneracies (Cs_2CeCu_3F_{12}) in the spin wa ve spectra and how this relates to the curvature and folding modes in the associated triangulated surface that characterize their ground states.\n\n Contact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Alexej Lunkin DTSTART;TZID=Europe/Berlin:20180712T160000 DTEND;TZID=Europe/Berlin:20180712T173000 DTSTAMP:20260527T090436Z UID:0000001268@events.thp.uni-koeln.de DESCRIPTION:Alexej Lunkin\, Landau Institute\, Moscow\n\nPerturbed Kitaev model: excitation spectrum and long-ranged spin correlations\n\nWe develop ed general approach to the calculation of power-law infrared asymptotics o f spin-spin correlation functions in the Kitaev honeycomb model with diffe rent types of perturbations. We have shown that in order to find these cor relation functions\, one can perform averaging of some bilinear forms comp osed out of free Majorana fermions\, and we presented the method for expli cit calculation of these fermionic densities. We demonstrated how to deriv e an effective Hamiltonian for the Majorana fermions\, including the effec ts of perturbations. For specific application of the general theory\, we h ave studied the effect of the Dzyaloshinskii-Moriya (DM) anisotropic spin- spin interaction\; we demonstrated that it leads\, already in the second o rder over its relative magnitude D/K\, to a power-law spin correlation fun ctions\, and calculated dynamical spin structure factor of the system. We have shown that an external magnetic field h in presence of the DM interac tion\, opens a gap in the excitation spectrum of magnitude proportional to Dh.\n\nContact Person: Dmitry Bagrets LOCATION:Seminar Room\, Alte Theorie END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Jan Gelhausen DTSTART;TZID=Europe/Berlin:20180727T100000 DTEND;TZID=Europe/Berlin:20180727T113000 DTSTAMP:20260527T090436Z UID:0000001306@events.thp.uni-koeln.de DESCRIPTION:Jan Gelhausen\n\nMagnetic Phase Transitions in Driven-Dissipat ive Atomic Ensembles Interacting with Quantum Light (PhD Defense)\n\n\n\nC ontact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Xiaoyu Wang DTSTART;TZID=Europe/Berlin:20180905T100000 DTEND;TZID=Europe/Berlin:20180905T113000 DTSTAMP:20260527T090436Z UID:0000001313@events.thp.uni-koeln.de DESCRIPTION:Xiaoyu Wang\, University of Chicago\n\nElectrical transport ne ar an Ising-nematic quantum critical point\n\nAn electronic Ising-nematic order spontaneously breaks the rotation symmetry of the underlying lattice down to two-fold. It has been observed in various systems\, in particular the cuprate and iron-based high temperature superconductors. In the vicin ity of a nematic quantum critical point — achieved by tuning some extern al parameter such as pressure or doping — the physics is described by th at of low-frequency long-wavelength order parameter fluctuations coupled t o a Fermi surface. However\, due to the momentum-conserving nature of the induced electron-electron interaction\, the temperature dependence of the resistivity near an Ising nematic QCP remains unclear. In this talk\, we s hed light on the problem by incorporating disorder and Umklapp process int o the low-energy theory. Our work can be viewed as solving an extended Bol tzmann equation\, with a collision integral that accounts for complicated multi-particle scattering processes important near the QCP.\n\nContact Per son: Carsten Bauer LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Krishanu Chowdhury DTSTART;TZID=Europe/Berlin:20180906T140000 DTEND;TZID=Europe/Berlin:20180906T153000 DTSTAMP:20260527T090436Z UID:0000001314@events.thp.uni-koeln.de DESCRIPTION:Krishanu Chowdhury\, Cornell/Nordita\n\nA classification of ma gnetic frustration and metamaterials from topology\n\nWe study the relatio nship between the physics of topology and zero modes in frustrated systems and metamaterials. Zero modes that exist in topological matters are disti nct from the ones arising from symmetry breaking. Incidentally\, a promine nt aspect of frustrated systems and metamaterials also is to harbor such k ind of zero modes in form of an accidental degeneracy. Taking cues from th ese two apparently different phenomena\, we ask a simple question: are the robust features of frustration topologically protected and if so can we c lassify different types of frustration using topology? In answering these questions we invoke the tools of topological mechanics to identify the key agent at play\, namely the rigidity matrix\, which is a non-Hermitian mat rix and decides the topology of spin-wave zero modes in a frustrated magne t or phonon modes in metamaterials. Further developments of the theory rel y on combining the recent developments in our understanding of Maxwell con straint counting and generalizing the ten-fold way classification of Hermi tian matrices to non-Hermitian matrices. The result is a three-fold way cl assification for each Maxwell counting index. We illustrate the classifica tion by demonstrating the existence of a new vortex-like invariant for rea l rigidity matrices using random matrices and through example frustrated s pin models. So by classifying all the rigidity matrices\, we answer the qu estion of the origin of frustration (i.e. zero modes in the form of accide ntal degeneracy) in a wide class of frustrated magnets and metamaterials b y linking it to topological invariants.\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Emilie Huffman DTSTART;TZID=Europe/Berlin:20180907T140000 DTEND;TZID=Europe/Berlin:20180907T153000 DTSTAMP:20260527T090436Z UID:0000001304@events.thp.uni-koeln.de DESCRIPTION:Emilie Huffman\, Uni Wuerzburg\n\nThe Fermion Bag Approach to Hamiltonian Theories\n\nQuantum Monte Carlo (QMC) methods\, when applicabl e\, offer dependable ways to extract the nonperturbative physics of strong ly-correlated many-body systems. However\, there are some formidable bottl enecks to the applicability of these methods such as the sign problem and algorithmic update inefficiencies. Using the t-V model Hamiltonian\, I dem onstrate how the fermion bag approach--originally developed in the context of Lagrangian lattice field theories--led to the first sign problem solut ion for this model. I then show how using fermion bag ideas to develop a n ew efficient QMC algorithm to study the t-V model allowed us to compute cr itical exponents for the chiral Ising universality class (involving one fl avor of four-component Dirac fermions) that seem to be more reliable than those from previous QMC calculations. Finally\, I discuss how the fermion bag approach offers certain advantages to the study of other models involv ing Dirac fermions and also extends to fermion-spin interactions and Z_2 g auge theories.\n\nContact Person: Michael Scherer LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Adrian Feiguin DTSTART;TZID=Europe/Berlin:20181115T100000 DTEND;TZID=Europe/Berlin:20181115T110000 DTSTAMP:20260527T090436Z UID:0000001354@events.thp.uni-koeln.de DESCRIPTION:Adrian Feiguin\, Northeastern University\n\nCompetition betwee n screening and indirect exchange: effects of geometry and dimensionality. \n\nIn the past decade we have witnessed enormous progress in experiments that consist of placing magnetic atoms at predetermined positions on subst rates and building magnetic nanostructures\, one atom at a time. The inter actions between magnetic moments are mediated by the conduction electrons through a mechanism understood in terms of a theory developed decades ago by Ruderman\, Kittel\, Kasuya\, and Yosida\, dubbed "RKKY theory"\, which applies when the spins are classical. The quantum nature of the electronic spin introduces another degree of complexity and competition with other q uantum phenomena: the Kondo effect. This competition is quite subtle and n on-trivial\, and can only be studied by numerical means. We explore these phenomena on different lattice geometries in 1\,2 and 3 dimensions by intr oducing an exact mapping onto an effective one-dimensional problem that we can solve with the density matrix renormalization group method (DMRG). We show a clear departure from conventional RKKY theory and important diffe rences that can be attributed to dimensionality and geometry. In particula r\, for the square and cubic lattices at half filling\, Kondo physics domi nates even at short distances\, while the ferromagnetic RKKY state is ener getically unfavorable\, translating into a finite range for the RKKY inter action. In the case of larger spin S=1\, RKKY correlations can coexist wit h (partial) screening.\n\nContact Person: Simon Trebst LOCATION:Konferenzraum Theorie\, Altbau END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Assa Auerbach DTSTART;TZID=Europe/Berlin:20181128T100000 DTEND;TZID=Europe/Berlin:20181128T110000 DTSTAMP:20260527T090436Z UID:0000001348@events.thp.uni-koeln.de DESCRIPTION:Assa Auerbach\, Technion\n\nHall Number of Strongly Correlated Metals\n\nAn exact formula for the temperature dependent Hall number of m etals is derived. It is valid for nonrelativistic fermions or bosons\, wit h an arbitrary potential and interaction. This dc transport coefficient is proven to (remarkably) depend solely on equilibrium susceptibilities\, wh ich are more amenable to numerical algorithms than the conductivity. An ap plication to strongly correlated phases is demonstrated by calculating the Hall sign in the vicinity of Mott phases of lattice bosons.\n\nContact Pe rson: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Piotr Surowka DTSTART;TZID=Europe/Berlin:20190118T140000 DTEND;TZID=Europe/Berlin:20190118T153000 DTSTAMP:20260527T090436Z UID:0000001363@events.thp.uni-koeln.de DESCRIPTION:Piotr Surowka\, MPI PKS Dresden\n\nTransport in semi-metals\n\ nI will review recent developments of transport in materials with a very s mall overlap between the bottom of the conduction band and the top of the valence band. I will focus on hydrodynamic and kinetic manifestations of c hiral anomalies. After introducing basic theoretical concepts I will discu ss relativistic Weyl particles. Next I will introduce materials\, the so-c alled multi-Weyl semi-metals\, which do not have relativistic dispersion y et are anomalous at the quantum level. Finally\, I will present recent dev elopments and challenges in measuring hydrodynamic transport of electrons in semi-metals.\n\nContact Person: Semyon Klevtsov LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Matthias Vojta DTSTART;TZID=Europe/Berlin:20190124T100000 DTEND;TZID=Europe/Berlin:20190124T113000 DTSTAMP:20260527T090436Z UID:0000001367@events.thp.uni-koeln.de DESCRIPTION:Matthias Vojta\, TU Dresden\n\nExotic Landau levels: From Majo rana fermions to supersymmetry\n\n\n\nContact Person: Achim Rosch / Simon Trebst LOCATION:Konferenzraum Theorie END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Mathias Scheurer DTSTART;TZID=Europe/Berlin:20190214T140000 DTEND;TZID=Europe/Berlin:20190214T153000 DTSTAMP:20260527T090436Z UID:0000001379@events.thp.uni-koeln.de DESCRIPTION:Mathias Scheurer\, Harvard University\n\nGauge theories of flu ctuating antiferromagnetism for the cuprates\n\n\n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.01\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Jinhong Park DTSTART;TZID=Europe/Berlin:20190318T110000 DTEND;TZID=Europe/Berlin:20190318T123000 DTSTAMP:20260527T090436Z UID:0000001378@events.thp.uni-koeln.de DESCRIPTION:Jinhong Park\, Weizmann Institute\n\nNoise on complex quantum Hall edges: ballistic electrical transport and heat diffusion\n\nElectrica l and thermal conductances of a quantum Hall bar reflect the topological s tructure of the incompressible bulk phase. \nHere we show that noise of el ectrical current carried through the edge evidences the interplay between these two topological observables. \nTransport through an edge of particle -hole conjugate states is modeled by a voltage-biased line junction made u p of counter-propagating modes. \nSpecifically\, we focus on the edge of a \\nu = 2/3 fractional quantum Hall state. Noise is generated at a point d istinctly separated from the hot spot \n(where most of the Ohmic dissipati on takes place) and reflects the competition between ballistically carried downstream current and diffusively carried heat (which can propagate also upstream). We propose specific setups where our predictions can be measur ed.\n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.01\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Ikuma Tateishi DTSTART;TZID=Europe/Berlin:20190531T140000 DTEND;TZID=Europe/Berlin:20190531T153000 DTSTAMP:20260527T090436Z UID:0000001420@events.thp.uni-koeln.de DESCRIPTION:Ikuma Tateishi\, University of Tokyo and University of Cologne \n\nThe topological phase classification based on the shape of nodal lines \n\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Urban Seifert DTSTART;TZID=Europe/Berlin:20190605T100000 DTEND;TZID=Europe/Berlin:20190605T113000 DTSTAMP:20260527T090436Z UID:0000001396@events.thp.uni-koeln.de DESCRIPTION:Urban Seifert\, TU Dresden\n\nMagnon-induced interactions: Fro m partial quantum disorder to novel probes\n\nIn magnetically ordered syst ems\, fluctuations on top of the ordered state in the form of magnons can induce effective interactions. These magnon-mediated interactions may act to stabilise exotic phases of matter\, and also significantly contribute t o non-equilibrium responses. I will discuss two recent examples.\nNumerica l results provide evidence for the existence of a partially disordered gro und state in the antiferromagnetic stuffed honeycomb lattice\, in which co llinearly ordered moments coexist with an only short-range correlated subs ystem. I show how magnons in the ordered honeycomb system mediate interact ions among the central spins and derive an effective model. Fluctuations n ear the transition between two competing ground states of the model are co njectured to lead to a quantum disordered ground state. I will further dis cuss how magnon interactions are crucial for the optical generation of coh erent magnons in easy-plane antiferromagnets\, with a particular focus on the spin-orbit Mott insulator Sr2IrO4. Here\, laser fields which directly couple to the local moments induce effective fields which drive a low-ener gy magnon\, giving rise to a finite out-of-plane magnetization. The subseq uent dynamics can be probed using a pump-probe protocol.\n\nContact Person : Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Jeremy Young DTSTART;TZID=Europe/Berlin:20190904T100000 DTEND;TZID=Europe/Berlin:20190904T110000 DTSTAMP:20260527T090436Z UID:0000001442@events.thp.uni-koeln.de DESCRIPTION:Jeremy Young\, University of Maryland\n\nDriven-dissipative co upled Ising models: a new non-equilibrium universality class\n\nDriven-dis sipative systems can potentially exhibit non-equilibrium phenomena that ar e absent in their equilibrium counterparts. However\, phase transitions pr esent in these systems generically exhibit an effectively classical\, equi librium behavior in spite of their non-equilibrium origin. In this talk\, I investigate an experimentally motivated model where two Ising-like order parameters interact and form a multicritical point. I will discuss how at such a multicritical point\, new non-equilibrium criticality can emerge. These non-equilibrium multicritical points exhibit a variety of exotic phe nomena with no counterpart in equilibrium\, including spiraling phase boun daries\, the emergence of discrete scale invariance rather than the more f amiliar continuous scale invariance\, and the violation of the fluctuation -dissipation theorem at all length scales\, resulting in a sytem which bec omes “hotter” and “hotter” at longer and longer wavelengths. Furth ermore\, I will discuss how for more complex order parameters with a diffe rent form of symmetry\, additional non-equilibrium multicritical points ca n emerge.\n\nContact Person: Sebastian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Christina Psadouraki DTSTART;TZID=Europe/Berlin:20191018T143000 DTEND;TZID=Europe/Berlin:20191018T153000 DTSTAMP:20260527T090436Z UID:0000001465@events.thp.uni-koeln.de DESCRIPTION:Christina Psadouraki\, University of Cologne\n\nNonequilibrium Quantum Dynamics of Magnetic Skyrmions\n\nWe study the quantum propagatio n of a skyrmion in chiral magnetic insulators by generalizing the micromag netic equations of motion. The fluctuations around the skyrmionic configur ation give rise to a damping derived microscopically\, which in some limit reduces to a skyrmion mass. We demonstrate that a skyrmion in a confined geometry behaves as a massive particle\, a discovery with great impact on the technologically important case of linear tracks relevant for magnetic memory devices. In the presence of time-dependent oscillating magnetic fie ld gradients\, the unavoidable coupling of the external field to the magno ns gives rise to time-dependent dissipation for the skyrmion\, with measur able consequences on the skyrmion path. These ac fields act as a net drivi ng force on the skyrmion via its own intrinsic magnetic excitations. We ge neralize the standard quantum theory of dissipation to include the stochas tic effects of the driven bath on the skyrmion dynamics. Our work initiate s studies towards the possibility of observing a quantum mechanical behavi or at a mesoscopic scale. I will briefly talk about the observability of t unneling events\, in particular quantum depinning of a magnetic skyrmion o ut of a pinning center.\n\nContact Person: Alex Altland LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Henry Legg DTSTART;TZID=Europe/Berlin:20191129T140000 DTEND;TZID=Europe/Berlin:20191129T153000 DTSTAMP:20260527T090436Z UID:0000001459@events.thp.uni-koeln.de DESCRIPTION:Henry Legg\n\nTransport and disorder in Dirac materials (PhD d efense)\n\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Shun Okumura DTSTART;TZID=Europe/Berlin:20191212T140000 DTEND;TZID=Europe/Berlin:20191212T153000 DTSTAMP:20260527T090436Z UID:0000001484@events.thp.uni-koeln.de DESCRIPTION:Shun Okumura\, University of Tokyo\n\nNumerical Study on Magne tic Hedgehog Lattices in Noncentrosymmetric Metals and their Field Depende nce\n\nRecently\, three-dimensional topological spin textures called the m agnetic hedgehog lattices (HLs) were discovered in the B20-type compounds MnSi1-xGex [1]. The HLs have periodic arrays of magnetic monopoles and ant i-monopoles\, which induce interesting transport phenomena\, such as the t opological Hall effect and the topological thermoelectric transport. Howev er\, their stabilization mechanism has not been fully understood thus far. Here we investigate the ground state of an effective spin model with long -range interactions arising from the itinerant nature of electrons by vari ational calculations and simulated annealing. We find that the HLs are sta bilized even at zero field by the synergetic effect of symmetric and antis ymmetric interactions from the spin-charge and spin-orbit couplings\, resp ectively. We clarify the full phase diagram in the magnetic field\, which includes multiple phase transitions with changes in the number of monopole s and anti-monopoles [2]. We also find that the monopoles and anti-monopol es move\, repel\, and pair annihilate with topological phase transition by increasing the magnetic field successively [3].\n\n[1] Y. Fujishiro et al .\, Nat. Commun. 10\, 1059 (2019).\n[2] S. Okumura\, S. Hayami\, Y. Kato\, and Y. Motome\, arXiv:1908.05044.\n[3] S. Okumura\, S. Hayami\, Y. Kato\, and Y. Motome\, arXiv:1909.01316.\n\nContact Person: Achim Rosch LOCATION:HS III END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Florian Lange DTSTART;TZID=Europe/Berlin:20200110T140000 DTEND;TZID=Europe/Berlin:20200110T153000 DTSTAMP:20260527T090436Z UID:0000001481@events.thp.uni-koeln.de DESCRIPTION:Florian Lange\n\nGiant response to weak pumping in the presenc e of approximate symmetries (PhD Defense)\n\n\n\nContact Person: not speci fied LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Jan Masell DTSTART;TZID=Europe/Berlin:20200313T140000 DTEND;TZID=Europe/Berlin:20200313T153000 DTSTAMP:20260527T090436Z UID:0000001504@events.thp.uni-koeln.de DESCRIPTION:Jan Masell\n\nManipulation of the helical phase of chiral magn ets with spintransfer torque\n\n\n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Nele Calebaut DTSTART;TZID=Europe/Berlin:20200618T100000 DTEND;TZID=Europe/Berlin:20200618T113000 DTSTAMP:20260527T090436Z UID:0000001540@events.thp.uni-koeln.de DESCRIPTION:Nele Calebaut\, Technion\n\nEmergence of gravity from 2D confo rmal field theory\n\nI will present three mechanisms for emergence of grav ity from 2D conformal field theory (CFT). Two of them are based on entangl ement\, exemplifying the intricate relation between quantum information an d quantum gravity\, and one on a deformation of the CFT with an irrelevant operator. While the context of this work is holography\, the mechanisms t hemselves are non-holographic. The resulting gravitational system is of di rect relevance to the set-up used in recent papers reporting significant p rogress on the black hole information paradox\n\nContact Person: Alexander Altland LOCATION:Zoom END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Laura Donnay DTSTART;TZID=Europe/Berlin:20200622T100000 DTEND;TZID=Europe/Berlin:20200622T113000 DTSTAMP:20260527T090436Z UID:0000001541@events.thp.uni-koeln.de DESCRIPTION:Laura Donnay\, Vienna\n\nInfinite-dimensional symmetries\, hol ography and black holes\n\nIn this talk\, I will review the recent advance s in the understanding of intriguing infinite-dimensional symmetries that emerge at the boundary of spacetimes. These symmetries play an important r ole in the description of many phenomena such as gravitational memory effe cts\, scattering amplitudes in flat space and black hole physics. By conne cting seemingly unrelated topics in theoretical physics\, infinite-dimensi onal symmetries have shed a new light on the fascinating universal feature s of gauge theories and gravity.\n\nContact Person: Alexander Altland LOCATION:Zoom END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Felix Haehl DTSTART;TZID=Europe/Berlin:20200622T150000 DTEND;TZID=Europe/Berlin:20200622T163000 DTSTAMP:20260527T090436Z UID:0000001542@events.thp.uni-koeln.de DESCRIPTION:Felix Haehl\, Princeton\n\nQuantum gravity through the hologra phic lens\n\nIn the search for a theory of quantum gravity that is able to resolve singularities in classical general relativity and explain the fir st moments of the universe\, string theory delivers powerful tools: the “holographic” AdS/CFT duality allows us to study quantum gravity using much better understood field theory methods. I will explain some of the p rogress towards an explicit decoding of relevant aspects of gravity from a holographic quantum field theory. I will particularly focus on the emerge nce of spacetime dynamics from quantum entanglement\, and on a new way to think about quantum chaos which serves as a useful diagnostic of black hol e physics.\n\nContact Person: Alexander Altland LOCATION:Zoom END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Gabor Sarosi DTSTART;TZID=Europe/Berlin:20200624T100000 DTEND;TZID=Europe/Berlin:20200624T113000 DTSTAMP:20260527T090436Z UID:0000001543@events.thp.uni-koeln.de DESCRIPTION:Gabor Sarosi\, CERN\n\nFrom quantum gravity to strongly couple d field theories\n\nThere is evidence that spacetime and gravity emerge fr om the dynamics of more fundamental\, strongly coupled degrees of freedom. The most concrete realization of this idea is the AdS/CFT paradigm\, wher e gravity is holographically encoded in the physics of certain conformal f ield theories. I will describe some of my contributions towards understand ing fundamental aspects of AdS/CFT\, in particular the search for the dual description of the volume of the emergent space\, and general results abo ut chaos and the quantum butterfly effect in strongly coupled quantum syst ems.\n\nContact Person: Alexander Altland LOCATION:Zoom END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Claire Zukovski DTSTART;TZID=Europe/Berlin:20200625T100000 DTEND;TZID=Europe/Berlin:20200625T113000 DTSTAMP:20260527T090436Z UID:0000001545@events.thp.uni-koeln.de DESCRIPTION:Claire Zukovski\, Amsterdam\n\nGeometry and Holography\n\nAbst ract: A major goal for theoretical physics is the unification of gravity w ith quantum mechanics. An important tool for tackling this question is hol ography\, or the duality between a theory of gravity and a conformal field theory in one lower dimension. In this talk I will address the question o f how to reconstruct the geometry of a gravitational spacetime with field theoretic tools\, relying on observables such as Wilson lines that are ame nable to quantization. I will invoke a varied toolkit drawing on technique s from many areas of physics and mathematics\, from quantum information to symplectic geometry. Importantly\, my focus will be on de Sitter spacetim e\, which closely resembles our actual universe\, and whose quantization c ould give insight into non-perturbative phenomena in cosmology.\n\nContact Person: Alexander Altland LOCATION:Zoom END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Magdalena Zych DTSTART;TZID=Europe/Berlin:20200625T150000 DTEND;TZID=Europe/Berlin:20200625T163000 DTSTAMP:20260527T090436Z UID:0000001546@events.thp.uni-koeln.de DESCRIPTION:Magdalena Zych\, Queensland\n\nComposite quantum systems at th e interplay with general relativity\n\nA major goal of modern physics is t o understand and test the regime where quantum mechanics and general relat ivity both play a role. However\, its distinctive effects are typically re levant at high energies or strong gravitational fields\, beyond the reach of present-day experiments. In this seminar I will discuss a different app roach\, focused on low-energy but composite quantum systems. Internal dyna mics of composite systems can act as a sensitive probe of relativistic eff ects even at low-energies and in weak gravitational fields -- I will expla in what quantum and general relativistic effects can arise for such system s and how they can be tested. I will outline the broader relevance of this approach for the research on joint foundations of quantum mechanics and g eneral relativity\, and for the future quantum-enhanced technologies such as metrology and sensing\, or information processing.\n\nContact Person: A lexander Altland LOCATION:Zoom END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Markus Schmitt DTSTART;TZID=Europe/Berlin:20200819T163000 DTEND;TZID=Europe/Berlin:20200819T173000 DTSTAMP:20260527T090436Z UID:0000001554@events.thp.uni-koeln.de DESCRIPTION:Markus Schmitt\, Berkeley\n\nQuantum many-body dynamics in 2D with novel variational approaches\n\nThe efficient numerical simulation of nonequilibrium real-time evolution in isolated quantum matter constitutes a key challenge for current computational methods. This holds in particul ar in the regime of two spatial dimensions\, whose experimental exploratio n is currently pushed forward using quantum simulators. In this talk I wil l discuss our recent efforts towards the development of versatile variatio nal approaches\, which are efficiently applicable also to two-dimensional systems. On the one hand\, a perturbatively motivated variational ansatz e nabled us to identify disorder-free localization in an interacting two-dim ensional lattice gauge theory [1]. On the other hand\, leveraging large sc ale computational resources\, we were able to demonstrate that neural netw ork wave functions can exceed the capabilities of tensor networks on the t ask of computing quench dynamics in the two-dimensional quantum Ising mode l [2].\n\n[1] P. Karpov et al.\, arXiv:2003.04901\n[2] M. Schmitt and M. H eyl\, arXiv:1912.08828\n\nContact Person: S. Trebst LOCATION:zoom / https://uni-koeln.zoom.us/j/93587244758 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Sourabh Patil DTSTART;TZID=Europe/Berlin:20200918T090000 DTEND;TZID=Europe/Berlin:20200918T103000 DTSTAMP:20260527T090436Z UID:0000001561@events.thp.uni-koeln.de DESCRIPTION:Sourabh Patil\, Sorbonne University\, Paris\n\nTriangular vort ex lattices in the Kitaev honeycomb model\, the sixteen-fold way and parit y of Chern numbers (PhD thesis application)\n\nKitaev proposed an interact ing model of spins (1/2) on a honeycomb lattice exactly solvable by mappin g onto free Majorana fermions coupled to a Z_2 gauge field\, hosting vorti ces (pi flux in a hexagon). In the presence of a time-reversal symmetry-br eaking term\, the ground state is gapped\, characterized by a Chern number v in Z and the system hosts anyonic excitations. The Chern number ν mod 16 specifies the type of anyonic excitations\, hence the sixteen-fold way. \nOur investigation in many well-chosen triangular vortex configurations ( and their duals) shows 14 out of 16 of these phases. The phases with v = + -7 are missing.\nIn a general case\, we prove that any periodic vortex con figuration with an odd number of vortices per geometric unit cell can only host even Chern numbers whereas odd Chern numbers can be found in other c ases.\n\nReference: J.N. Fuchs\, S. Patil\, J. Vidal\, https://arxiv.org/a bs/2005.03655\n\nPeople interested in chatting with the speaker please let it know to Matteo Rizzi\, who will organize a schedule accordingly.\n\nCo ntact Person: Matteo Rizzi LOCATION:BlueJeans END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Yizhi You DTSTART;TZID=Europe/Berlin:20201211T140000 DTEND;TZID=Europe/Berlin:20201211T153000 DTSTAMP:20260527T090436Z UID:0000001571@events.thp.uni-koeln.de DESCRIPTION:Yizhi You\, MPI PKS Dresden\n\nEmergent fractons in Elusive Bo se Metal --- When IR theory blend with UV physics\n\nIn this talk\, I wil l show that the defects of the valence plaquette solid(VPS) order paramete r\, in addition to possessing non-trivial quantum numbers\, have fracton m obility constraints in the VPS phase. The spinon inside a single vortex ca nnot move freely in any direction\, while a dipolar pair of vortices with spinon pairs can only move perpendicular to its dipole moment. These mobil ity constraints\, while they persist near QCP\, can potentially inhibit th e condensation of spinons and preclude a continuous transition from the VP S to the Néel antiferromagnet. Instead\, the VPS melting transition can b e driven by the proliferation of spinon dipoles. In particular\, we argue that a 2d VPS can melt into a stable gapless phase in the form of an algeb raic bond liquid with algebraic correlations and long-range entanglement. Such a bond liquid phase yields a concrete example of the elusive 2d Bose metal with symmetry fractionalization.\n\nContact Person: Alexander Altlan d LOCATION:https://uni-koeln.zoom.us/j/92092707566?pwd=Sy9vTWRXNG5SeHNCN2tEa HNtbXRDdz09 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Guo-Yi Zhu DTSTART;TZID=Europe/Berlin:20210108T140000 DTEND;TZID=Europe/Berlin:20210108T153000 DTSTAMP:20260527T090436Z UID:0000001589@events.thp.uni-koeln.de DESCRIPTION:Guo-Yi Zhu\, MPI-PKS\, Dresden\n\nSubdiffusive dynamics and cr itical quantum correlations in a disorder-free localized Kitaev honeycomb model out of equilibrium\n\nThe Kitaev honeycomb model is well-known to ho st a quantum spin liquid at zero temperature\, exhibiting topological orde r and fractionalization of spin into emergent Majorana fermion minimally c oupled with Z2 gauge field. The exact solvability of this model stems from the conservation of local gauge fluxes\, which also has dramatic impact u pon the nonequilibrium dynamics when the system is brought out of equilibr ium and isolated from any environment. The latter issue has been widely st udied in the quest of emergent ergodicity in generic quantum manybody syst ems\, or ergodicity breaking in manybody localization or other mechanisms. In this talk\, I will show that the homogeneous Kitaev model exhibits the phenomenon of disorder-free localization\, where the fractionalized Major ana fermion is partially localized by the Z2 gauge flux disorder dynamical ly generated in a highly excited state. As a result\, the system exhibits exotic quench dynamics that is neither MBL nor ergodic: (1) algebraic ligh tcone of dimer correlation spreading\; (2) algebraic decaying critical cor relation in late time steady state\; (3) algebraic growth of projective bi partite entanglement entropy to a volume law. Further\, I will show numeri cal evidence that the long time feature is stable against solvability brea king perturbation. Our results may possibly imply nontrivial dimer correla tion for Kitaev spin liquids at finite temperature.\n\nContact Person: Sim on Trebst LOCATION:https://uni-koeln.zoom.us/j/93649501617?pwd=UVFUT2thakZ4U2N2VlpWa zNDb1FRUT09 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Bjoern Sbierski DTSTART;TZID=Europe/Berlin:20210115T160000 DTEND;TZID=Europe/Berlin:20210115T173000 DTSTAMP:20260527T090436Z UID:0000001592@events.thp.uni-koeln.de DESCRIPTION:Bjoern Sbierski\, UC Berkeley\n\nSpins\, Pseudo-Majoranas\, an d the functional RG\n\nSpins can be represented in terms of complex fermio nic operators. This allows for a direct application of many-body technique s like the functional RG approach to frustrated quantum magnets. However\, as the representation above introduces unphysical Hilbert space sectors\, the applicability of this approach at finite temperatures is questionable . Here\, I review an alternative Majorana fermion representation of spins which does not introduce any unphysical states. We develop a general funct ional RG formalism for Majoranas and apply it to the Pseudo-Majorana repre sentation of Heisenberg models on small spin clusters as well as frustrate d square and triangular lattices. We compute the finite temperature behavi or of spin correlations and thermodynamic quantities and compare to exact diagonalization and the high-temperature series expansion.\n\nContact Pers on: Simon Trebst LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Daniel Alcalde Puente DTSTART;TZID=Europe/Berlin:20210115T140000 DTEND;TZID=Europe/Berlin:20210115T153000 DTSTAMP:20260527T090436Z UID:0000001593@events.thp.uni-koeln.de DESCRIPTION:Daniel Alcalde Puente\, Ruhr Universität Bochum\n\nConvolutio nal restricted Boltzmann machine aided Monte Carlo: An application to Isin g and Kitaev models\n\nMachine learning is becoming widely used in analyzi ng the thermodynamics of many-body condensed matter systems. Restricted Bo ltzmann machine (RBM) aided Monte Carlo simulations have sparked interest recently\, as they manage to speed up classical Monte Carlo simulations. I n the talk\, based on my recently published paper (Phys. Rev. B 102\, 1951 48)\, I will explain how we used the convolutional restricted Boltzmann ma chine (CRBM) method to reduce the number of parameters to be learned drast ically by taking advantage of translation invariance. Furthermore\, I will show that it is possible to train the CRBM at smaller lattice sizes\, and apply it to larger lattice sizes. To demonstrate the efficiency of CRBM\, I show the application to the Ising and honeycomb Kitaev models.\n\nConta ct Person: Matteo Rizzi LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Tobias Bouma DTSTART;TZID=Europe/Berlin:20210122T140000 DTEND;TZID=Europe/Berlin:20210122T153000 DTSTAMP:20260527T090436Z UID:0000001594@events.thp.uni-koeln.de DESCRIPTION:Tobias Bouma\, University of Amsterdam\n\nSolitons in the repu lsive one-dimensional Bose gas\n\nIn this presentation\, the emergence of localised\, stable wave packets (solitons) is investigated in the context of the repulsive one-dimensional Bose gas. In the weakly interacting limit \, the gas is approximated by the classical non-linear Schrödinger equati on\, of which it is known that such classical localisation occurs. A natur al question to ask would be whether these classical wave packets could be reproduced starting from the quantum non-linear Schrödinger equation\, an d if so\, which quantum mechanical wave function would produce such densit y profiles. Previous research has indeed attempted to do so\, however\, th ese studies had two main limitations: 1) only the attractive regime was in vestigated\, which has limited physical significance because there is no s aturation\, and 2) localisation was shown only in limiting cases. In the t alk\, some of the mathematical steps are outlined in an attempt to overcom e these two shortcomings. Besides introductory material\, the talk is spli t into three parts according to the results obtained: 1) numerical results are discussed that show whether the desired localisation even exists outs ide the weakly interacting regime\, 2) analytical efforts are discussed th at show that Dirichlet kernels arise from the density form factor and fina lly 3) I will share some of the analytical efforts on simplifying general density form factors\, which are of relevance when comparing magnitudes be tween form factor terms. It is found that mutually repulsive particles exp erience attraction at the macroscopic level\, outside of the weakly and ma ximally interacting limits.\n\nContact Person: Matteo Rizzi LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Oliver Lunt DTSTART;TZID=Europe/Berlin:20210125T091500 DTEND;TZID=Europe/Berlin:20210125T100000 DTSTAMP:20260527T090436Z UID:0000001597@events.thp.uni-koeln.de DESCRIPTION:Oliver Lunt\, University College London\n\nPhase transitions i n non-equilibrium quantum matter\n\nMuch insight has come from the idea th at non-equilibrium systems can exhibit phenomena not found in thermal equi librium. Understanding these non-equilibrium phases and the transitions be tween them is a major research frontier of modern many-body physics. In my talk I will outline two examples of novel physics found in non-equilibriu m quantum systems. The first\, discrete time crystals (DTCs)\, are a proto typical example of a non-equilibrium phase of matter\, defined by the fact that they spontaneously break time-translation symmetry. I will describe the results of an experiment involving the observation of a DTC in a doped semiconductor platform\, where both interactions and dissipation play a s ignificant role in stabilizing the DTC order. Next I will discuss measurem ent-induced transitions\, which are a new class of phase transition in ope n quantum systems. I will focus on two aspects of these transitions: the e ffect of the underlying unitary dynamics on the nature of the phase transi tion\, and the role of dimensionality in determining the universal propert ies at criticality.\n\nContact Person: not specified LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Seth Davis DTSTART;TZID=Europe/Berlin:20210125T153000 DTEND;TZID=Europe/Berlin:20210125T161500 DTSTAMP:20260527T090436Z UID:0000001604@events.thp.uni-koeln.de DESCRIPTION:Seth Davis\, Rice University\n\nNon-Markovian dephasing of dis ordered\, quasi-one-dimensional fermion systems\n\nAs a potential window o n transitions out of the ergodic\, many-body-delocalized phase\, we study the\ndephasing of weakly disordered\, quasi-one-dimensional fermion system s due to a diffusive\, non-\nMarkovian noise bath. This bath is generated by inelastic scattering due to short-ranged interactions. We calculate the dephasing of weak localization perturbatively through second order in the bath coupling. However\, we find that instabilities in the calculation si gnal a failure of the self-consistent Born approximation. We also consider a many-channel quantum wire where short-ranged\, spin-exchange interactio ns coexist with screened Coulomb interactions. We calculate the dephasing rate\, treating the short-ranged interactions perturbatively and the Coulo mb interaction exactly. The latter provides a physical infrared regulariza tion that stabilizes perturbation theory at long times\, giving the first controlled calculation of quasi-1D dephasing due to diffusive noise. Our r esults are relevant to the search for precursors to the MBL transition tha t can be understood in the high-T ergodic phase. As a bonus\, the calculat ion also provides a mechanism for the enhancement of dephasing at low temp eratures in spin SU(2)-symmetric quantum wires\, beyond the Altshuler-Aron ov-Khmelnitsky result. The enhancement is possible due to the amplificatio n of the triplet-channel interaction strength\, and provides an additional mechanism that could contribute to the experimentally observed low-temper ature saturation of the dephasing time.\n\nContact Person: not specified LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Nagara Srinivasa DTSTART;TZID=Europe/Berlin:20210126T091500 DTEND;TZID=Europe/Berlin:20210126T100000 DTSTAMP:20260527T090436Z UID:0000001598@events.thp.uni-koeln.de DESCRIPTION:Nagara Srinivasa\, MPIPKS\n\nSpecial states in quantum many-bo dy spectra\n\nTypically\, a generic quantum many-body system under isolat ion is known to thermalize. However\, there are exceptions where thermaliz ation is violated. For instance\, while a strong violation of thermalizati on occurs in the well known many-body localizing systems (MBL)\, a viola tion in the weaker sense occurs through the phenomenon of quantum many-bod y scars (QMBS). In this talk\, I will first review both MBL and QMBS. I wi ll then describe our recent work where we showed that an emergent symmetry in a single eigenstate of a disordered model protects it from MBL while n ot preventing the rest of the states in the spectrum from many-body locali zing. I will motivate how such an example calls for exploring "inverted qu antum scars"\, namely\, non-area law states embedded in a spectrum of loca lized states. Time permitting\, I will also walk you through our other rec ent works where we construct topologically ordered scarred models.\n\nCont act Person: not specified LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Tian Mao Tan DTSTART;TZID=Europe/Berlin:20210127T143000 DTEND;TZID=Europe/Berlin:20210127T151500 DTSTAMP:20260527T090436Z UID:0000001599@events.thp.uni-koeln.de DESCRIPTION:Tian Mao Tan\, University of Chicago\n\nOperator Entanglement as a probe of information scrambling and quantum chaos\n\nThe characteriza tion of quantum chaos in many-body systems has been an active area of rese arch in the past several years. There have been several proposed diagnosti cs of quantum chaos\, like the out-of-time-ordered correlators and the spe ctral form factor\, to name a few. The focus of this talk is another quant ity known as the operator entanglement. A particularly interesting measure of operator entanglement is the tripartite operator mutual information wh ich is a quantitative measure of the amount of information delocalization. By studying the tripartite operator mutual information of both unitary op erators and local operators in a variety of systems ranging from conformal field theories to spin chains\, we demonstrate the utility of operator en tanglement in distinguishing chaotic and non-chaotic theories.\n\nContact Person: not specified LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Yanbai Zhang DTSTART;TZID=Europe/Berlin:20210129T140000 DTEND;TZID=Europe/Berlin:20210129T153000 DTSTAMP:20260527T090436Z UID:0000001595@events.thp.uni-koeln.de DESCRIPTION:Yanbai Zhang\, TU München (Visiting Scholar)\n\nTopological M agnon Insulators in Kagome Lattice: Decay and Renormalization\n\nIt has be en predicted that topological magnon insulators are realized in kagome pla ne of pyrochlore magnetic insulators with Dzyaloshinskii-Moriya interactio n. Bosonic topological insulators can exhibit a topological band structure . Although bosonic system ground state is trivial condensate or the vacuum \, their excited states may carry signatures of the topology. In this pres entation\, I will show the distinct features of excitations in kagome latt ice within the framework of the spin-wave theory: (a) finite lifetime at zero temperature due to spontaneous two-magnon decays\, (b) the renormaliz ation of magnon energy depending on the magnetization direction\, (c) sing ularities in the decay rate. Those features are shown in the form of dynam ical structure factors. Their effect in experimentally detecting edge mode s will also be discussed.\n\nContact Person: Matteo Rizzi LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Abishodh Prakash DTSTART;TZID=Europe/Berlin:20210201T091500 DTEND;TZID=Europe/Berlin:20210201T100000 DTSTAMP:20260527T090436Z UID:0000001600@events.thp.uni-koeln.de DESCRIPTION:Abishodh Prakash\, ICTS\, Bengaluru\, Karnataka\, Indiai\n\nAs pects of quantum matter in and out of equilibrium\n\nThe talk is in three parts.\n\nPart 1: Universal spectral signatures of many-body-localization\ nThe notion of universality is enormously powerful in understanding equili brium phases and phenomena. At the most practical level\, it allows us to substitute a complicated problem for a much simpler one. A surprising noti on of universality has been observed for quantum chaotic systems\, which a re said to constitute a non-equilibrium 'eigenstate phase' of matter. Corr elations in the spectrum are observed to be reproduced by a particularly s imple system- random matrix ensembles\, which predict universal signatures \, such as a `ramp' in the spectral-form-factor. I will argue the existenc e of analogous universal signatures for a different eigenstate phase cons tituted by many-body-localized systems. Based on joint work with Manas Kul karni (ICTS-TIFR) and Jedediah Pixley (Rutgers).\n\nPart 2: Eigenstate pha ses with non-Abelian symmetry.\nA long-standing open question is whether t here exist any eigenstate phases beyond the now-well-known examples of man y-body-localized or quantum-chaotic systems. A promising possibility prese nts itself for systems with finite non-Abelian symmetries. By numerically studying a spin-chain with such a symmetry in the presence of disorder\, w e see some evidence for the presence of a novel eigenstate phase of matter . Based on joint work with Tzu-Chieh Wei (Stony Brook)\, Sriram Ganeshan ( CCNY) and Lukasz Fidkowski (University of Washington).\n\nPart 3: Emergent supersymmetry in fermionic symmetry-protected-topological phases.\nSymmet ry-protected topological phases are characterized by an almost trivial ins ulating bulk but exotic boundaries due to the presence of 't Hooft anomali es. These anomalies present themselves in manifold ways- protected gapless phases\, Landau-forbidden deconfined quantum critical transitions and the absence of a trivial order. I will demonstrate that for a large class of fermionic SPT phases\, the boundary anomaly presents itself in a fascinati ng manner- emergent supersymmetry with no fine tuning of any kind! This mi ght present the most robust realization of supersymmetry in solid-state an d cold atomic systems. Based on joint work with Juven Wang (Harvard)\n\nCo ntact Person: not specified LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Shovan Dutta DTSTART;TZID=Europe/Berlin:20210202T091500 DTEND;TZID=Europe/Berlin:20210202T100000 DTSTAMP:20260527T090436Z UID:0000001601@events.thp.uni-koeln.de DESCRIPTION:Shovan Dutta\, University of Cambridge\n\nLong-range entanglem ent and multiple steady states in a lossy qubit array\n\nEnvironmental cou pling typically drives a quantum system to a unique steady state with very little coherence\, which is a major obstacle for quantum information proc essing. I will talk about a simple experimental setting of an array of two -level systems with localised pump and loss that has multiple highly coher ent steady states\, including maximally entangled states of nonlocal Bell pairs. Such states originate from a hidden symmetry that conserves Bell pa irs over long distances\, leading to controllable long-range entanglement. I will discuss how to selectively prepare and observe these states in a b road range of present-day setups.\n\nContact Person: not specified LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Orazio Scralatella DTSTART;TZID=Europe/Berlin:20210204T091500 DTEND;TZID=Europe/Berlin:20210204T100000 DTSTAMP:20260527T090436Z UID:0000001602@events.thp.uni-koeln.de DESCRIPTION:Orazio Scralatella\, College de France\n\ntba\n\n\n\nContact P erson: not specified LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Aleksandra Ziolkowska DTSTART;TZID=Europe/Berlin:20210205T091500 DTEND;TZID=Europe/Berlin:20210205T100000 DTSTAMP:20260527T090436Z UID:0000001603@events.thp.uni-koeln.de DESCRIPTION:Aleksandra Ziolkowska\, Oxford\n\nYang-Baxter Integrable Lindb lad Equations\n\nOpen quantum systems are ubiquitous in the contexts of at omic and molecular physics\, circuit QED and optomechanics. Couplings to a n environment can also have very interesting effects on the dynamics of ma ny-particle quantum systems. In order to arrive at a tractable description of such problems\, it is customary to work within the Markovian approxima tion\, whereby the system is described by a Lindblad master equation. Whil e much progress has been made in analysing Lindblad equations for many-par ticle systems by employing\, for example\, perturbative and matrix product states methods\, it is clearly highly desirable to have exact solutions i n specific\, and hopefully representative\, cases. This talk aims to show that for a number of interacting open quantum systems\, it is possible to obtain exact analytic solutions through a connection with integrable model s. I will describe how a correspondence between a Lindblad equation and an integrable Hamiltonian can be established and what information about the open systems it provides. In particular\, I will discuss the equivalence i n structure of generalised Hubbard models and vectorised Lindblad equation s\, which are already visible in the R-matrix of the integrable model. I w ill also mention how this construction can be extended by focusing purely on the integrability of the invariant subspaces of the Lindblad equations. The talk is based on the work presented in SciPost Phys. 8\, 044 (2020) ( doi: 10.21468/SciPostPhys.8.3.044).\n\nContact Person: not specified LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Yannik Schaden DTSTART;TZID=Europe/Berlin:20210324T100000 DTEND;TZID=Europe/Berlin:20210324T110000 DTSTAMP:20260527T090436Z UID:0000001610@events.thp.uni-koeln.de DESCRIPTION:Yannik Schaden\, University of Cologne\n\nFermi-surface pinnin g in van Hove doped graphene\n\n\n\nContact Person: Michael Scherer LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Aiman Al-Eryani DTSTART;TZID=Europe/Berlin:20210325T100000 DTEND;TZID=Europe/Berlin:20210325T110000 DTSTAMP:20260527T090436Z UID:0000001609@events.thp.uni-koeln.de DESCRIPTION:Aiman Al-Eryani\, Tübingen University\n\nFunctional Renormali sation Group Analysis of the Pseudo-critical scales in the Attractive Hubb ard model\n\n\n\nContact Person: Michael Scherer LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Wenzhe Deng DTSTART;TZID=Europe/Berlin:20210326T100000 DTEND;TZID=Europe/Berlin:20210326T110000 DTSTAMP:20260527T090436Z UID:0000001611@events.thp.uni-koeln.de DESCRIPTION:Wenzhe Deng\, University of Melbourne\n\nDensity matrix renorm alization group and applications to spin-1/2 chains\n\n\n\nContact Person: Michael Scherer LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/92374710227 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Markus Weissenhofer DTSTART;TZID=Europe/Berlin:20211105T140000 DTEND;TZID=Europe/Berlin:20211105T153000 DTSTAMP:20260527T090436Z UID:0000001669@events.thp.uni-koeln.de DESCRIPTION:Markus Weissenhofer\, University of Konstanz\n\nThermally acti vated dynamics of magnetic skyrmions\n\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Frank Schlawin DTSTART;TZID=Europe/Berlin:20211208T140000 DTEND;TZID=Europe/Berlin:20211208T153000 DTSTAMP:20260527T090436Z UID:0000001686@events.thp.uni-koeln.de DESCRIPTION:Frank Schlawin\, University of Hamburg\n\nCavity-mediated inte ractions in cold atoms and quantum material\n\n\n\nContact Person: not spe cified LOCATION:Seminar Room\, II Physics Institute END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Alex Kruchkov DTSTART;TZID=Europe/Berlin:20211221T140000 DTEND;TZID=Europe/Berlin:20211221T153000 DTSTAMP:20260527T090436Z UID:0000001687@events.thp.uni-koeln.de DESCRIPTION:Alex Kruchkov\, EPFL / Harvard\n\nEngineering flat electronic bands from first mathematical principles\n\nEngineering flat electronic ba nds from first mathematical principles \n\nAlexander Kruchkov\nInstitute o f Physics\, EPFL\, Lausanne\, Switzerland\n\nDepartment of Physics\, Harva rd University\, USA Branco Weiss Society in Science\, ETH Zurich\, Switzer land\n\n\nThe concept of flat electronic bands is a change of paradigm in condensed matter physics. In this talk\, I will address the origin of band flatness and its connection to the quantum geometry of electronic states. 1 My work focuses on engineering the flat topological bands from the first mathematical principles\, namely the Riemannian metrics and quantum geome try\, with consequent holomorphicity and meromorphicity of the flat band s tates\,1\,2\,3 enforced with accurate atomistic compu­ tations\, DFT and tight binding with lattice relaxation effects.4\,5 It provides deep insigh ts on the origin of band flatness\, which should be looked for in the real space (rather than in momentum space as conventionally it had been). In t he complicated and messy domain of band structure computations\, the devel oped approach provides an aesthetical tool for engineering flat electronic bands in realistic materials4 with consequent experimental confirmation.6 \,7 Time permitting\, I will address the novel formalism of flat­band qua ntum transport built on the concepts of quantum geometry.8\n\nReferences:\ n\n[1] A. Kruchkov\, Origin of band flatness and constraints of higher Che rn numbers\, arXiv 2105.14672 (2021).\n[2.] G. Tarnopolsky\, A. J. Kruchko v\, A. Vishwanath\, Origin of magic angles in twisted bilayer graphene\, P hysical Review Letters 122\, 106405 (2019). [3.] E. Khalaf\, A. J. Kruchko v\, G. Tarnopolsky\, A. Vishwanath\, Magic angle hierarchy in twisted grap hene multilayers\, Physical Review B 100\, 085109 (2019).\n[4.] S. Carr\, C. Li\, Z. Zhu\, E. Kaxiras\, S. Sachdev\, A.J. Kruchkov\, Ultraheavy and ultrarelativistic Dirac quasiparticles in sandwiched graphenes\, Nano Lett ers (2020).\n[5.] F. Haddadi\, Q. Wu\, A. J. Kruchkov\, O.V. Yazyev\, Moir é flat bands in twisted double bilayer graphene\, Nano Letters (2020).\n[ 6.] J.M. Park\, Y. Cao\, K. Watanabe\, T. Taniguchi\, P. Jarillo­Herrero\ , Tunable strongly coupled superconductivity in magic­angle twisted trila yer graphene\, Nature volume 590\, (2021).\n[7.] Z. Hao\, A. M. Zimmerman\ , P. Ledwith\, E Khalaf\, D. Najafabadi\, K. Watanabe\, T. Taniguchi\, A. Vishwanath\, P. Kim\, Electric field–tunable superconductivity in altern ating­twist magic­angle trilayer graphene\, Science 371\, 6534 (2021).\n [8.] A. Kruchkov\, Quantum transport in dispersionless electronic bands\, in preparation (2021).\n\nContact Person: Alex Altland LOCATION:zoom / https://uni-koeln.zoom.us/j/6555080253?pwd=MzVmM0xiZ2FRYmU 2M05GUko0aVc4UT09 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Peter Cha DTSTART;TZID=Europe/Berlin:20220117T160000 DTEND;TZID=Europe/Berlin:20220117T173000 DTSTAMP:20260527T090436Z UID:0000001678@events.thp.uni-koeln.de DESCRIPTION:Peter Cha\, Cornell\n\nAttention-based State Characterization\ n\nWith rapid progress across platforms for quantum systems\, the problem of many-body quantum state reconstruction for noisy quantum states becomes an important challenge. There has been a growing interest in approaching the problem of quantum state reconstruction using generative neural networ k models. In this talk\, I will present the 'attention-based quantum tomog raphy' (AQT)\, a method of quantum state reconstruction that uses an atten tion mechanism-based generative network. The results demonstrate not only that AQT outperforms earlier neural-network-based quantum state reconstruc tion on identical tasks but that AQT can accurately reconstruct the densit y matrix associated with a noisy quantum state experimentally realized in an IBMQ quantum computer. In addition\, I will highlight broader applicati ons of AQT currently being developed.\n\nContact Person: Simon Trebst LOCATION:Seminarraum Altbau Theorie END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Nils Niggemann DTSTART;TZID=Europe/Berlin:20220124T160000 DTEND;TZID=Europe/Berlin:20220124T170000 DTSTAMP:20260527T090436Z UID:0000001692@events.thp.uni-koeln.de DESCRIPTION:Nils Niggemann\, FU Berlin\n\nQuantitative FRG in frustrated 3 D Magnets\n\nFrustrated three dimensional quantum magnets bear a rich phen omenology but are notoriously hard to treat theoretically. We show how a M ajorana representation of spin operators\, in combination with the functio nal renormalization group allows for quantiative simulations at finite tem peratures. Focusing on Heisenberg magnets\, we establish a finite-size sca ling approach and extract accurate results for critical temperatures and - exponents. Further\, we quantify and discuss the improvements introduced b y two-loop contributions in the flow equations applied to the Pyrochlore l attice. We then investigate the accuracy of its prominent spin-ice rule un der the influence of both quantum and thermal fluctuations.\n\nContact Per son: Dominik Kiese LOCATION:Seminarraum Altbau Theorie END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Dominic Williamson DTSTART;TZID=Europe/Berlin:20220427T100000 DTEND;TZID=Europe/Berlin:20220427T113000 DTSTAMP:20260527T090436Z UID:0000001716@events.thp.uni-koeln.de DESCRIPTION:Dominic Williamson\, University of Sydney\n\nFun with fractons \n\nTopological phases of matter have been the subject of intense interest since the discovery of the fractional quantum hall effect. More recently they have come to underpin leading approaches to quantum error correction. To date\, the focus has remained on topological phases in two dimensions and the anyon models that describe them. In three dimensions our understan ding is significantly less developed\, the existence of immobile quasipart icles known as fractons opens up a landscape of intricate possibilities. T he immobility of fractons leads to new possible symmetry actions\, subdime nsional phase transitions\, and glassy dynamics that can be harnessed to p roduce more robust quantum codes. In this talk I will give an overview of recent efforts to develop a systematic understanding of fracton topologica l phases and what this might tell us about three dimensional topological c odes.\n\nContact Person: Guo-Yi Zhou LOCATION:Zoom (https://uni-koeln.zoom.us/j/96646818958 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Johannes Hofmann DTSTART;TZID=Europe/Berlin:20220429T140000 DTEND;TZID=Europe/Berlin:20220429T153000 DTSTAMP:20260527T090436Z UID:0000001715@events.thp.uni-koeln.de DESCRIPTION:Johannes Hofmann\, Weizmann Institute\n\nSuperconductivity\, c harge density wave\, and supersolidity in flat bands with tunable quantum metric\n\nPredicting the fate of an interacting system in the limit \nwhe re the electronic bandwidth is quenched is often highly non-trivial. \nThe complex interplay between interactions and quantum fluctuations \ndriven by the band geometry can drive a competition between various \nground stat es\, such as charge density wave order and superconductivity. \nIn this wo rk\, we study an electronic model of topologically-trivial flat \nbands wi th a continuously tunable Fubini-Study metric in the presence of \non-site attraction and nearest-neighbor repulsion\, using numerically \nexact qua ntum Monte Carlo simulations. By varying the electron filling \nand the sp atial extent of the localized flat-band Wannier wavefunctions\, \nwe obtai n a number of intertwined orders. These include a phase with \ncoexisting charge density wave order and superconductivity\, i.e.\, a \nsupersolid. I n spite of the non-perturbative nature of the problem\, we \nidentify an a nalytically tractable limit associated with a `small' \nspatial extent of the Wannier functions\, and derive a low-energy \neffective Hamiltonian th at can well describe our numerical results.\nIf time permits\, I will also discus some preliminary quantum Monte Carlo \nresults for twisted bilayer graphene at charge neutrality.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.01\, ETP and Zoom (https://uni-koeln.zoom.us/j/921 65384988) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Samuel Garratt DTSTART;TZID=Europe/Berlin:20220615T100000 DTEND;TZID=Europe/Berlin:20220615T113000 DTSTAMP:20260527T090436Z UID:0000001738@events.thp.uni-koeln.de DESCRIPTION:Samuel Garratt\n\nNonlocal conspiracies in the measurement of critical many-body quantum states\n\nI will discuss the effects of local m easurements on critical quantum ground states. These states are highly ent angled and feature algebraic correlations between local observables. As a consequence\, local measurements can have highly nonlocal effects. Our foc us is on Tomonaga-Luttinger liquid (TLL) ground states\, a continuous fami ly of critical states in one dimension whose structure is parameterized by a Luttinger parameter K. We show that arbitrarily weak local measurements \, performed over extended regions of space\, can conspire to drive transi tions in long-wavelength correlations. Conditioning first on a particular measurement outcome we show that there is a transition in the character of the resulting quantum state for K<1\, and highlight a formal analogy with the effect of an impurity on transport. To study the full ensemble of mea surement outcomes we consider averages of physical quantities which are ne cessarily nonlinear in the system density matrix. We show how their behavi our can be understood within a replica field theory\, and for the measurem ents that we consider we find that the symmetry of the theory under exchan ge of replicas is broken for K<1/2. For K<1/2 there is a suppression of qu antum fluctuations of measured observables which becomes more prominent at long wavelengths.\n\nContact Person: Michael Buchhold LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Aditi Mitra DTSTART;TZID=Europe/Berlin:20220711T140000 DTEND;TZID=Europe/Berlin:20220711T153000 DTSTAMP:20260527T090436Z UID:0000001746@events.thp.uni-koeln.de DESCRIPTION:Aditi Mitra\, NYU\n\nFloquet chains and the stability of their edge modes\n\nFloquet or periodically driven systems show topological pha ses that are qualitatively different from their static counterparts. In th is talk I will first introduce the new kinds of topological phases that ca n be realized in free-fermion Floquet systems. I will then show that the e dge modes encountered in certain free fermion Floquet systems are remarkab ly robust to adding interactions\, even in disorder-free systems where gen eric bulk quantities can heat to infinite temperatures due to the periodic driving. This robustness of the edge modes to heating can be understood i n the language of strong modes for free fermion chains\, and almost stron g modes for interacting chains. I will then outline a tunneling calculatio n for extracting the long lifetimes of these edge modes by mapping the Hei senberg time-evolution of the edge operator to dynamics of a single partic le in Krylov subspace.\n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.02\, ETP and Zoom (https://uni-koeln.zoom.us/j/921 65384988 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Nikita Kavokine DTSTART;TZID=Europe/Berlin:20221028T140000 DTEND;TZID=Europe/Berlin:20221028T153000 DTSTAMP:20260527T090436Z UID:0000001760@events.thp.uni-koeln.de DESCRIPTION:Nikita Kavokine\, Max Planck - NYC Center for Nonequilibrium Quantum Phenomena\n\nQuantum plumbing: the mysteries of nanoscale flows\n\ nLiquids are usually described within classical physics\, whereas solids r equire the tools of quantum mechanics. I will show how in nanoscale system s this distinction no longer holds. At these scales\, liquid flows may in fact exhibit quantum effects as they interact with electrons in the solid walls. I will first discuss the quantum friction phenomenon\, where charge fluctuations in the liquid interact with electronic excitations in the so lid to produce a hydrodynamic friction force. Using many-body quantum theo ry\, we predict that this effect is particularly important for water flowi ng on carbon-based materials\, and we obtain experimental evidence of the underlying mechanism from pump-probe terahertz spectroscopy. I will then s how how the theory can be pushed one step further to describe hydrodynamic Coulomb drag - the generation of electric current by a liquid in the soli d along which it flows. This phenomenon involves a subtle interplay of ele ctrostatic and electron-phonon interactions\, and suggests strategies for designing materials with low hydrodynamic friction.\n\nContact Person: Sim on Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Arnob Kumar Ghosh DTSTART;TZID=Europe/Berlin:20221104T121500 DTEND;TZID=Europe/Berlin:20221104T134500 DTSTAMP:20260527T090436Z UID:0000001758@events.thp.uni-koeln.de DESCRIPTION:Arnob Kumar Ghosh\, Institute of Physics Bhubaneswar\n\nDynami cal construction of higher-order topological systems\n\n\n\nContact Person : Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Alex Wietek DTSTART;TZID=Europe/Berlin:20221125T140000 DTEND;TZID=Europe/Berlin:20221125T153000 DTSTAMP:20260527T090436Z UID:0000001757@events.thp.uni-koeln.de DESCRIPTION:Alex Wietek\, MPI-PKS Dresden\n\nTunable Stripe Order in the M oire Hubbard Model and Fragmentation of Cooper Condensates\n\nTwisted moir e materials have gained much attention since the recent discovery of super conductivity in twisted bilayer graphene. These materials offer an excitin g new experimental platform to study the physics of strongly correlated el ectrons. The moire Hubbard model describes correlations in certain homobil ayer twisted transition metal dichalcogenides. In this talk\, I will prese nt our recent results on the essential properties of this system. Using ex act diagonalization and density matrix renormalization group methods\, we find magnetic Mott insulating and metallic phases\, which\, upon doping ex hibit intertwined charge and spin ordering and\, in some regimes\, pair bi nding of holes. The phases are highly tunable via an interlayer potential difference. Remarkably\, the hole binding energy is found to be highly tun able revealing an experimentally accessible regime where holes become attr active. Moreover\, I will present a novel approach to diagnosing supercond ucting Cooper condensation based on the structure of the two-body density matrix. I find that a superconducting condensate can be fragmented into pa rtial condensates living on the charge stripes of a system.\n\nReferences: \n[1] Tunable Stripe Order and Weak Superconductivity in the Moire Hubbard Model\, A. Wietek\, J. Wang\, J. Zang\, J. Cano\, A. Georges\, A. Millis\ , Phys. Rev. Research 4\, 043048 (2022)\n[2] Fragmented Cooper pair conden sation in striped superconductors\, A. Wietek\, Phys. Rev. Lett. 129\, 177 001\, Editors suggestion (2022)\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Kotaro Shimuzu DTSTART;TZID=Europe/Berlin:20221130T100000 DTEND;TZID=Europe/Berlin:20221130T113000 DTSTAMP:20260527T090436Z UID:0000001771@events.thp.uni-koeln.de DESCRIPTION:Kotaro Shimuzu\, The University of Tokyo\n\nPhase degree of fr eedom in multiple-Q spin textures\n\nTopological spin textures\, such as t wo-dimensional skyrmion lattices (SkLs) and three-dimensional hedgehog lat tices (HLs) are approximately represented by superpositions of multiple sp in density waves\, and hence\, called multiple-Q spin textures. In such sp in structures\, the phase degree of freedom of the superposed waves plays an important role in the topological properties as well as the symmetry of the magnetic textures\, but the systematic investigation has not been per formed thus far.\nIn this study\, we theoretically investigate the evoluti on of magnetic and topological properties in SkLs composed of three spin d ensity waves (3Q-SkL) and HLs composed of four spin density waves (4Q-HL) while changing the phases as well as the magnetization. By introducing a h yperspace to deal with the phases systematically\, we find that the 3Q-SkL s change their skyrmion number among -2\, -1\, 0\, 1\, and 2 depending on the phase and magnetization. In the case of the 4Q-HLs\, we clarify that t he density and configuration of topological objects called hedgehogs and a ntihedgehogs change in a wide range. Our results provide good references t o discuss how the actual systems experience the magnetic and topological t ransitions in an applied magnetic field.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP and zoom (https://uni-koeln.zoom.us/j/921 65384988 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Filip Rozpedek DTSTART;TZID=Europe/Berlin:20221201T160000 DTEND;TZID=Europe/Berlin:20221201T170000 DTSTAMP:20260527T090436Z UID:0000001794@events.thp.uni-koeln.de DESCRIPTION:Filip Rozpedek\, University of Chicago\n\nML4Q concept seminar series "Quantum Communication"\n\nQuantum Repeaters for Quantum Communica tion\n\nQuantum channels enable the implementation of communication tasks inaccessible to their classical counterparts. The most famous example is t he distribution of secret key. However\, in the absence of quantum repeate rs\, the rate at which these tasks can be performed is dictated by the los ses in the quantum channel. In practice\, channel losses have limited the reach of quantum protocols to short distances. Quantum repeaters have the potential to significantly increase the rates and reach beyond the limits of direct transmission. This talk will provide a high-level overview of di fferent types of the proposed quantum repeater architectures. We will then look at the specific techniques that these schemes utilise in order to ac hieve long distance quantum communication\, analyse their strengths and li mitations as well as discuss the required hardware needed to implement the m. Finally\, I will introduce a novel type of quantum repeater schemes whi ch make efficient use of the quantum communication channels by encoding qu antum information in the bosonic error-correcting codes.\n\nContact Person : Anne Matthies LOCATION:Zoom (https://uni-koeln.zoom.us/j/91902676314?pwd=SFAyR1kxRUYwV3h DRjhVWDdoTDNEdz09 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Vastal Dwivedi DTSTART;TZID=Europe/Berlin:20221206T160000 DTEND;TZID=Europe/Berlin:20221206T170000 DTSTAMP:20260527T090436Z UID:0000001796@events.thp.uni-koeln.de DESCRIPTION:Vastal Dwivedi\, FU Berlin\n\nTwisted Weyl semimetal interface s\n\nA remarkable feature of Weyl semimetals (WSMs) is Fermi arcs - anomal ous surface states that connect Weyl nodes of opposite chirality. At the i nterface betweem two WSMs\, they can instead connect Weyl nodes of the sam e chirality\, leading to perfect transmission of electrons across the inte rface. In this talk\, I will describe some recent work on the magnetic bre akdown of electron transport in this setup. For an interface between WSMs twisted relative to one another\, we show that a longitudinal magnetic fie ld leads to a suppression of conductance owing to Landau-Zener tunneling b etween the interface modes of opposite chirality.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Denis Golez DTSTART;TZID=Europe/Berlin:20221208T140000 DTEND;TZID=Europe/Berlin:20221208T153000 DTSTAMP:20260527T090436Z UID:0000001790@events.thp.uni-koeln.de DESCRIPTION:Denis Golez\, Ljubljana\n\nCompressing quantum dynamics\n\n\n\ nContact Person: Achim Rosch LOCATION:Seminar Room 0.01\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Zala Lenarcic DTSTART;TZID=Europe/Berlin:20221209T140000 DTEND;TZID=Europe/Berlin:20221209T153000 DTSTAMP:20260527T090436Z UID:0000001789@events.thp.uni-koeln.de DESCRIPTION:Zala Lenarcic\, Ljubljana\n\nPerturbed integrable systems\n\nI ntegrable systems typically exhibit non-generic transport properties. The spin 1/2 Heisenberg model is particularly rich\, with ballistic transport of energy and different regimes of spin transport\, including ballistic\, diffusive\, and super-diffusive ones. I will discuss the fate of the diffu sive and super-diffusive regimes under different types of Hamiltonian pert urbations and show that symmetry of perturbations can play an important ro le. For example\, perturbations that respect the SU(2) symmetry of the iso tropic Heisenberg model can cause anomalous transport behaviour even away from exact integrability.\nIn the second part\, I will focus on Markovian perturbations and propose a new Krylov space-type approach for an efficien t steady-state description of weakly driven and open\, nearly integrable s ystems. Lindblad dissipator will be used to add the most necessary conserv ation laws iteratively and thus increase the interpretability of stabilize d non-thermal steady states.\n\nContact Person: Achim Rosch LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Glaucia Murta DTSTART;TZID=Europe/Berlin:20221215T110000 DTEND;TZID=Europe/Berlin:20221215T120000 DTSTAMP:20260527T090436Z UID:0000001795@events.thp.uni-koeln.de DESCRIPTION:Glaucia Murta\, HHU Düsseldorf\n\nML4Q concept seminar series "Quantum Communication"\n\nDevice-independent quantum cryptography\n\nIn this talk I will introduce the device-independent framework\, and explain how the violation of a Bell inequality can be used to certify the security of cryptographic protocols. I will discuss how device-independent cryptog raphy leads to security even when the underlying system and measurement se tups are not well characterized or provided by an untrustworthy provider. Finally I will comment on the theoretical and experimental challenges and the progress in implementing device-independent quantum key distribution.\ n\nContact Person: Anne Matthies LOCATION:Zoom (https://uni-koeln.zoom.us/j/91902676314?pwd=SFAyR1kxRUYwV3h DRjhVWDdoTDNEdz09 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Urban Seifert DTSTART;TZID=Europe/Berlin:20230109T140000 DTEND;TZID=Europe/Berlin:20230109T150000 DTSTAMP:20260527T090436Z UID:0000001807@events.thp.uni-koeln.de DESCRIPTION:Urban Seifert\, Kavli Institute for Theoretical Physics\n\nMoi re spin liquids\n\nIn the past few years\, van der Waals heterostructures have emerged as a new platform for studying frustrated magnetic systems\, both in structures with layers exhibiting intrinsic magnetism\, as well as "Hubbard model simulators" such as moiré transition metal dichalcogenide s (TMD).\nI will first discuss bilayer U(1) Dirac spin liquids\, with the homogenously stacked system being unstable towards spontaneous symmetry br eaking. We show that adding a relative twist between the two layers soften s the ordering instability\, and the resulting ordered phase features a tu neable lattice of magnetic vortices.\nIn the second part of my talk\, I wi ll present ongoing work on correlated insulating states at fractional fill ings in moiré TMD bilayers\, where the formation of self-organized charge lattices has been observed experimentally. We describe these ordered stat es and explore the possibility of spin-liquid states within a slave-rotor mean-field theory.\n\nContact Person: Simon Trebst LOCATION:Seminar Room\, old theory building END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Finn Lasse Buessen DTSTART;TZID=Europe/Berlin:20230111T140000 DTEND;TZID=Europe/Berlin:20230111T150000 DTSTAMP:20260527T090436Z UID:0000001808@events.thp.uni-koeln.de DESCRIPTION:Finn Lasse Buessen\, University of Toronto\n\nDistributed Quan tum Computing\n\n\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Ronald de Wolf DTSTART;TZID=Europe/Berlin:20230112T110000 DTEND;TZID=Europe/Berlin:20230112T120000 DTSTAMP:20260527T090436Z UID:0000001802@events.thp.uni-koeln.de DESCRIPTION:Ronald de Wolf\, Dutch Centre for Mathematics and Computer Sci ence\n\nML4Q CSS "Quantum Algorithms - Introductory Talk"\n\n\n\nContact Person: Anne Matthies LOCATION:Zoom (https://uni-koeln.zoom.us/j/91902676314?pwd=SFAyR1kxRUYwV3h DRjhVWDdoTDNEdz09 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Simon Apers DTSTART;TZID=Europe/Berlin:20230119T110000 DTEND;TZID=Europe/Berlin:20230119T120000 DTSTAMP:20260527T090436Z UID:0000001803@events.thp.uni-koeln.de DESCRIPTION:Simon Apers\, IRIF (Université de Paris)\n\nML4Q CSS "Quantu m Algorithms - Quantum Random Walks"\n\n\n\nContact Person: Anne Matthies LOCATION:Zoom (https://uni-koeln.zoom.us/j/91902676314?pwd=SFAyR1kxRUYwV3h DRjhVWDdoTDNEdz09 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Victor Albert DTSTART;TZID=Europe/Berlin:20230126T160000 DTEND;TZID=Europe/Berlin:20230126T170000 DTSTAMP:20260527T090436Z UID:0000001804@events.thp.uni-koeln.de DESCRIPTION:Victor Albert\, University of Maryland and NIST\n\nML4Q CSS " Quantum Algorithms - Bosonic Codes"\n\n\n\nContact Person: Anne Matthies LOCATION:Zoom (https://uni-koeln.zoom.us/j/91902676314?pwd=SFAyR1kxRUYwV3h DRjhVWDdoTDNEdz09 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Karim Chahine DTSTART;TZID=Europe/Berlin:20230201T160000 DTEND;TZID=Europe/Berlin:20230201T170000 DTSTAMP:20260527T090436Z UID:0000001814@events.thp.uni-koeln.de DESCRIPTION:Karim Chahine\, SISSA\n\nCharge and spin instabilities in the kagome lattice extended Hubbard model\n\nThe recent discovery of the famil y of AV3Sb5 (A=K\, Cs\, Rb) metals has sparked great interest in the study of kagome lattice systems. These materials exhibit a plethora of intrigui ng low-temperature behaviour\, as superconductivity\, a charge density wav e (CDW) and time-reversal symmetry breaking (TRSB) without magnetic orderi ng have all been found within these compounds. Although much effort has be en devoted to understanding the physics of these materials in the last few years\, there are still many unknowns. For instance\, the nature of TRSB is still unclear\, as is the mechanism that stabilizes the CDW found. In t his work\, we study a model of interacting electrons on the kagome lattice at a mean-field level. In particular\, both a single-orbital model and a multi-orbital extension are considered. Our calculations reveal the presen ce of different interaction-driven CDW patterns\, with the single-orbital model exhibiting a CDW phase compatible with the experimental findings. Fu rthermore\, no traces were found of TRSB without magnetic ordering nor of ferromagnetism\, in accordance with recent variational Monte Carlo calcula tions. Our results also suggest that the px and py orbitals of the in-plan e Sb atoms might not be crucial for determining the physical properties of AV3Sb5 materials\, while the van Hove singularities in the band structure could be playing a key role in this regard.\n\nContact Person: Sebastian Diehl LOCATION:Seminar Room 0.01\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Jeongwan Haah DTSTART;TZID=Europe/Berlin:20230202T170000 DTEND;TZID=Europe/Berlin:20230202T180000 DTSTAMP:20260527T090436Z UID:0000001805@events.thp.uni-koeln.de DESCRIPTION:Jeongwan Haah\, Microsoft\n\nML4Q CSS "Quantum Algorithms - F loquet Codes"\n\n\n\nContact Person: Anne Matthies LOCATION:Zoom (https://uni-koeln.zoom.us/j/91902676314?pwd=SFAyR1kxRUYwV3h DRjhVWDdoTDNEdz09 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Nathanan Tantivasadakarn DTSTART;TZID=Europe/Berlin:20230203T140000 DTEND;TZID=Europe/Berlin:20230203T153000 DTSTAMP:20260527T090436Z UID:0000001811@events.thp.uni-koeln.de DESCRIPTION:Nathanan Tantivasadakarn\, Caltech\n\nTopological order from f inite-depth circuits and measurements: from theory to quantum devices\n\nA fundamental distinction between many-body quantum states are those with s hort- and long-range entanglement (SRE and LRE). The latter\, such as cat states\, topological order\, or critical states cannot be created by finit e-depth circuits. Remarkably\, examples are known where LRE is obtained by performing single-site measurements on SRE states such as preparing the t oric code from measuring a sublattice of a 2D cluster state. I will presen t a general framework of how and why these known protocols give rise to lo ng range entanglement based on interpreting the cluster state measurement as implementing the non-local Kramers-Wannier transformation. This provide s a scalable and practical way to 'gauge' a symmetry using only finite-dep th circuits and measurements\, and moreover allows us to go beyond the pre paration of stabilizer states. In addition\, we find a complexity hierarch y on long-range entangled states based on the minimal number of measuremen t layers required to create the state. I will argue that certain phases of matter cannot be prepared using any finite number of layers\, while remar kably certain non-Abelian topological orders can be prepared in a single r ound of measurement. As an application\, I will outline how current NISQ d evices\, such as Rydberg atom arrays and Google's quantum processors\, can scalably prepare a large class of exotic phases such as non-Abelian topol ogical order and even fracton phases.\n\nThis talk is based on 2112.01519\ , 2112.03061\, 2209.03964\, and 2209.06202\n\nContact Person: Guo-Yi Zhu LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Kae Nemoto DTSTART;TZID=Europe/Berlin:20230209T110000 DTEND;TZID=Europe/Berlin:20230209T120000 DTSTAMP:20260527T090436Z UID:0000001806@events.thp.uni-koeln.de DESCRIPTION:Kae Nemoto\, National Institute of Informatics\, Japan\n\nML4Q CSS "Quantum Algorithms - Quantum systems and Machine learning"\n\nWe ha ve recently seen the emergence of quantum processors with more than 50 qub its. This has initiated a huge world-wide effort to utilize this new compu tational power. However so far it has not been that easy to extract the co mputational power promised in those quantum processors. Quantum neural net works has been seen as an approach\, through which we might be able to fac ilitate these new quantum systems for computational tasks. In this seminar \, I introduce several ideas with quantum neural networks and present a ne w quantum computational model which utilizes scale-free networks in the Hi lbert space generated by the quantum processors. This quantum computationa l model is based on both reservoir computation and extreme machine learnin g and inherits their advantages. We discuss its potential and the advantag es it provides.\n\nContact Person: Anne Matthies LOCATION:Zoom (https://uni-koeln.zoom.us/j/91902676314?pwd=SFAyR1kxRUYwV3h DRjhVWDdoTDNEdz09 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Igor Poboiko DTSTART;TZID=Europe/Berlin:20230526T140000 DTEND;TZID=Europe/Berlin:20230526T153000 DTSTAMP:20260527T090436Z UID:0000001849@events.thp.uni-koeln.de DESCRIPTION:Igor Poboiko\, Karlsruhe Institute of Technology\n\nTheory of free fermions under random projective measurements\n\nWe develop an analyt ical approach to the study of one-dimensional free fermions subject to ran dom projective measurements of local site occupation numbers\, based on th e Keldysh path-integral formalism and replica trick. In the limit of rare measurements\, \\gamma / J << 1 (where \\gamma is measurement rate per sit e and J is hopping constant in the tight-binding model)\, we derive a non- linear sigma model (NLSM) as an effective field theory of the problem. Its replica-symmetric sector is described by a U(2) / U(1) x U(1) ~ S2 sigma model with diffusive behavior\, and the replica-asymmetric sector is a two -dimensional NLSM defined on SU(R) manifold with the replica limit R -> 1. On the Gaussian level\, valid in the limit \\gamma / J -> 0\, this model predicts a logarithmic behavior for the second cumulant of number of parti cles in a subsystem and for the entanglement entropy. However\, the one-lo op renormalization group analysis allows us to demonstrate that this logar ithmic growth saturates at a finite value ~(J / \\gamma)^2 even for rare m easurements\, which corresponds to the area-law phase. This implies the ab sence of a measurement-induced entanglement phase transition for free ferm ions. The crossover between logarithmic growth and saturation\, however\, happens at exponentially large scale\, ln(l_corr) ~ J / \\gamma. This make s this crossover very sharp as a function of the measurement frequency \\g amma/J\, which can be easily confused with a transition from the logarithm ic to area law in finite-size numerical calculations. We have performed a careful numerical analysis\, which supports our analytical predictions.\n\ nContact Person: Michael Buchhold LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Johannes Hofmann DTSTART;TZID=Europe/Berlin:20230623T140000 DTEND;TZID=Europe/Berlin:20230623T153000 DTSTAMP:20260527T090436Z UID:0000001860@events.thp.uni-koeln.de DESCRIPTION:Johannes Hofmann\, Weizmann Institute\n\nUncovering Conformal Symmetry in the 3D Ising Transition\n\nThe 3D Ising transition\, the most celebrated and unsolved critical phenomenon in nature\, has long been conj ectured to have emergent conformal symmetry\, similar to the case of the 2 D Ising transition. Yet\, the emergence of conformal invariance in the 3D Ising transition has rarely been explored directly\, mainly due to unavoid able mathematical or conceptual obstructions. Here\, we design an innovati ve way to study the quantum version of the 3D Ising phase transition on sp herical geometry\, using the fuzzy (noncommutative) sphere regularization. We accurately calculate and analyze the energy spectra at the transition\ , and explicitly demonstrate the state-operator correspondence (i.e.\, rad ial quantization)\, a fingerprint of conformal field theory. In particular \, we identify13 parity-even primary operators within a high accuracy and two parity-odd operators that were not known before. Our result directly e lucidates the emergent conformal symmetry of the 3D Ising transition\, a c onjecture made by Polyakov half a century ago. More importantly\, our appr oach opens a new avenue for studying 3D conformal field theories by making use of the state-operator correspondence and spherical geometry.\n\nConta ct Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Zhuo-Yu Xian DTSTART;TZID=Europe/Berlin:20230627T160000 DTEND;TZID=Europe/Berlin:20230627T170000 DTSTAMP:20260527T090436Z UID:0000001864@events.thp.uni-koeln.de DESCRIPTION:Zhuo-Yu Xian\, Julius Maximilian University of Würzburg\n\nQu antum chaos and Krylov complexity\n\nThe Krylov complexity measures the sp read of the wavefunction in the Krylov basis\, which is constructed using the Hamiltonian and an initial state. In this work (arXiv:2303.12151)\, we investigate the evolution of the maximally entangled state in the Krylov basis for both chaotic and non-chaotic systems. Our findings suggest that neither the linear growth nor the saturation of Krylov complexity is neces sarily associated with chaos. However\, for chaotic systems\, we observe a universal rise-slope-ramp-plateau behavior in the transition probability from the initial state to a Krylov basis\, which is a characteristic of ch aos in the spectrum of the Hamiltonian. Additionally\, the long ramp in th e transition probability is directly responsible for the late-time peak of Krylov complexity observed in previous literature. On the other hand\, fo r non-chaotic systems\, the transition probability exhibits a different be havior without the long ramp. Therefore\, our results help to clarify whic h features of the wave function time evolution in Krylov space characteriz e chaos.\n\nContact Person: Guo-Yi Zhu LOCATION:Seminar Room\, old theory building END:VEVENT BEGIN:VEVENT SUMMARY:CMT | L. Weigand DTSTART;TZID=Europe/Berlin:20230901T140000 DTEND;TZID=Europe/Berlin:20230901T153000 DTSTAMP:20260527T090436Z UID:0000001878@events.thp.uni-koeln.de DESCRIPTION:L. Weigand\n\nUntersuchung von Quanten-Magnetismus in geschich teten zwei-dimensionalen Gittern\n\nBachelor-Kolloquium\n\nContact Person: Matteo Rizzi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Ara Sedrakyan DTSTART;TZID=Europe/Berlin:20231020T140000 DTEND;TZID=Europe/Berlin:20231020T153000 DTSTAMP:20260527T090436Z UID:0000001895@events.thp.uni-koeln.de DESCRIPTION:Ara Sedrakyan\, Alikhanyan Natonal Science Laboratory\, Yere van\, Armenia\n\nPlateau transitions in Quantum Hall Effect: Role of rando mness of the network.\n\nNumerical calculations of the critical exponent o f the localization length\nin the Chalker-Coddington (CC) model (\\nu ~2. 6) differ considerably from the experimental \nvalue (\\nu~ 2.38) at the integer quantum Hall transition (IQHT). We review most of models\nconsider ed recently\, revile the origin of differences and the physics behind.\n The difference comes from the fact\, that in CC model disorder of pot ential is not \nfully taken into account. Besides the phase factor disorde r\, coming from Bohm-Aharonov \n phase in the magnetic field\, there is a structural disorder\, connected with randomness\n of the position of sadd le points of the random potential. At this points quantum\n tunneling is happening between Fermi lakes of the electrons in the potential landscap e\, \n which leads to change of localization length index \\nu . We sugge st\, that interaction \n between electrons and atoms at the lattice sites affect disorder character of potential \n and\, at the quasiclassical limi t\, on addition to U(1) phase disorder of CC model we \n have effective on e particle random network model with structural disorder . \n In paper PRB.95\, 125414 (2017) we propose a model for structural \n disor der\, where numerical simulation on the basis of transfer matrix approach give \n a value \\nu = 2.37 \\pm 0.017\, very close to the experimental value. \n Currently we have developed new technique of calculations and have launched new simulations \nof \\nu based on S-matrix approach. Preliminary results confirm correctness of the value obtained earlier on basis of transfer matrix approach. \n We discuss also the role and validity of Harris criteria in a presence of structural \n disorder and ar gue\, that the criteria should be modified.\n\nContact Person: Alexander A ltland LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Markus Schmitt DTSTART;TZID=Europe/Berlin:20231024T153000 DTEND;TZID=Europe/Berlin:20231024T170000 DTSTAMP:20260527T090436Z UID:0000001896@events.thp.uni-koeln.de DESCRIPTION:Markus Schmitt\, Uni Regensburg\n\nNeural quantum states: an o verview\n\nNeural quantum states (NQS) are emerging as a versatile tool to tackle the quantum many-body problem. In particular\, when dealing with c orrelated lattice models in intermediate spatial dimensions or with more c omplex interaction patterns\, such as those occurring in molecules\, NQS a pproaches have been shown to expand our computational capabilities. After introducing the basic ideas of the numerical machinery\, I will give an ov erview of recent developments in the field.\n\nContact Person: Simon Trebs t LOCATION:Seminar Room 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Xhek Turkeshi DTSTART;TZID=Europe/Berlin:20231024T140000 DTEND;TZID=Europe/Berlin:20231024T150000 DTSTAMP:20260527T090436Z UID:0000001898@events.thp.uni-koeln.de DESCRIPTION:Xhek Turkeshi\, University of Cologne\n\nError-resilience Phas e Transitions in Encoding-Decoding Quantum Circuits\n\nUnderstanding how e rrors deteriorate the information encoded in a many-body quantum system is a fundamental problem with practical implications for quantum technologie s. Here\, we investigate a class of encoding-decoding random circuits with coherent errors. The existence of a phase transition separating an error- protecting phase at weak error strength from an error-vulnerable phase is analytically demonstrated. We derive exact expressions showing that this t ransition is accompanied by an area-to-volume law entanglement transition and a localization transition in the computational basis. The emergence of multifractal features in the considered system is highlighted.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Giuliano Giudici DTSTART;TZID=Europe/Berlin:20231027T163000 DTEND;TZID=Europe/Berlin:20231027T173000 DTSTAMP:20260527T090436Z UID:0000001881@events.thp.uni-koeln.de DESCRIPTION:Giuliano Giudici\, University of Insbruck and Planqc\n\nTopolo gical quantum matter in Rydberg atom simulators\n\nProgrammable Rydberg at om arrays stand out as extremely powerful platforms for the quantum simula tion of strongly correlated states of matter. Their versatility lies in th e adaptable geometry of the trapping lattice and in the wide variety of co ntrollable atomic levels\, which naturally yields several distinct interac tion regimes.\nIn a journey through the most recent theoretical and experi mental achievements\, I will show how these devices enable synthesizing an d probing many-body states with topological order. Starting from the van d er Waals-interacting regime\, I will demonstrate that Rydberg Hamiltonians can host Z2 quantum spin liquids and analyze optimal protocols for their dynamical preparation. I will then introduce a novel class of Z3 spin liqu ids and engineer viable implementations in Rydberg atom setups. Finally\, I will consider a system of 3-level atoms coupled via a time-reversal symm etry-breaking dipolar exchange interaction and provide numerical evidence for the emergence of gapped chiral spin liquids with the same form of topo logical order of the fractional quantum Hall effect.\n\nContact Person: Si lvia Pappalardi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Roman Rausch DTSTART;TZID=Europe/Berlin:20231206T160000 DTEND;TZID=Europe/Berlin:20231206T173000 DTSTAMP:20260527T090436Z UID:0000001908@events.thp.uni-koeln.de DESCRIPTION:Roman Rausch\, TU Braunschweig\n\nTerminable transitions in a topological fermion ladder\n\nInteracting fermion ladders are important pl atforms to study quantum phases of matter including various Mott insulator s with different symmetry properties\, such as the D-Mott and S-Mott phase . The latter hold pre-formed electron pairs and become paired liquids (d-w ave and s-wave) upon doping. These Mott insulators were believed to be dis tinct phases (see e.g. the classical textbook “Quantum physics in one di mension”). We demonstrate that this understanding is incomplete: They ar e in fact two facets of the same interaction-induced topological phase. Wi th this\, we provide a quantum analog of the well-known terminable liquid- gas transition. However\, the phenomenology we uncover is even richer\, as in contrast to the liquid-gas transition\, the order of the transition ca n be tuned by the interaction and bears relevance for the topological prop erties of the system. These results show interesting synergy between funda mental questions in the fields of fermion pairing\, topology\, Mott insula tors and terminated phase transitions.\n\nContact Person: Matteo Rizzi LOCATION:Seminar Room 0.03\, ETP (+Zoom\, if requested) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Julio C. Magdalena de la Fuente DTSTART;TZID=Europe/Berlin:20240117T100000 DTEND;TZID=Europe/Berlin:20240117T113000 DTSTAMP:20260527T090436Z UID:0000001920@events.thp.uni-koeln.de DESCRIPTION:Julio C. Magdalena de la Fuente\, FU Berlin\n\nUnderstanding l ogical channels graphically: Quantum Error Correction in spacetime\n\nUnde rstanding and protecting against errors happening on a quantum device cons titute one of the biggest challenges in developing a fault-tolerant quantu m computing architecture. Recently\, the focus of the community shifted fr om a static perspective\, where information is encoded into a (fixed) subs pace\, to a dynamical perspective where one allows for the logical subspac e to change over time [1]\, with the most famous example being Floquet cod es\, error-correcting protocols defined by a periodic sequence of low-weig ht non-commuting (Pauli) measurements [2]. Understanding and analyzing suc h protocols in the presence of errors is an important challenge to devise and to understand new fault-tolerant protocols. We argue that tensor netwo rk methods inspired by the ZX calculus are good tools to analyze the error -correction properties of dynamical protocols as they allow for a simple\, graphical\, yet complete understanding of the evolution of logical inform ation through a circuit\, also in the presence of errors [3].\n\nIn this t alk\, I want to give an introduction on how to represent circuits composed of Clifford unitaries and Pauli measurements graphically. First\, I intro duce the elementary tensors from which one can build tensor networks resem bling the circuits of the above form. To understand error-correcting prope rties of a circuit expressed as a tensor network\, I introduce the notion of *projective Pauli flow* in terms of projective symmetries of the buildi ng blocks of the network [4]. I will show how all quantities needed to per form error-correction on a circuit can be understood graphically as differ ent types of Pauli flow.\nIf time allows\, I show how local relations amon gst the elementary tensors can be used to ‘deform’ a circuit into a di fferent\, but equivalent one [3\,5]. Importantly\, these local deformation s preserve the global Pauli flows and with that the logical action of the circuit and certain error-correction properties. This allows to transform given error-correcting circuits into new ones while preserving their error -correcting nature.\n\n[1] Delfosse\, Paetznick\; “Spacetime codes of Cl ifford circuits”\, arXiv:2304.05943\n[2] Hastings\, Haah\; “Dynamicall y Generated Logical Qubits”\, arXiv:2107.02194\n[3] Bombin et al\; “Un ifying flavors of fault tolerance with the ZX calculus”\, arXiv:2303.088 29\n[4] Magdalena de la Fuente\, Old\, et al.\; in preparation\n[5] Townse nd-Teague\, Magdalena de la Fuente\, Kesselring\; “Floquetifying the Col our Code”\, arXiv:2307.11136\n\nContact Person: Guo-Yi Zhu LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Poetri Tarabunga DTSTART;TZID=Europe/Berlin:20240119T140000 DTEND;TZID=Europe/Berlin:20240119T153000 DTSTAMP:20260527T090436Z UID:0000001913@events.thp.uni-koeln.de DESCRIPTION:Poetri Tarabunga\, ICTP Trieste\n\nMagic in many-body systems: tensor network approaches\n\nNonstabilizerness - commonly known as magic - quantifies resources beyond\nClifford operations and is a fundamental re source for achieving universal\nquantum computation. Recently\, several te nsor network methods have been\ndeveloped for computing the stabilizer Ren yi entropy (SRE)\, a recently\nintroduced measure of magic. These methods have unveiled intriguing\ninsights into the behavior and properties of mag ic in many-body systems.\nIn this talk\, I will introduce a new approach t o compute the magic\, by\nrepresenting the expectation values of Pauli str ings as matrix product\nstate (MPS). This method paves the way for calcula ting various measures of\nmagic\, including the SRE\, the stabilizer nulli ty\, and the Bell magic.\nFurthermore\, it allows for extracting the stabi lizer group of an MPS. Our\nmethod opens up the possibilty for exploring g enuine magic within\nmany-body systems.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Meng-Yuan Li DTSTART;TZID=Europe/Berlin:20240126T144500 DTEND;TZID=Europe/Berlin:20240126T154500 DTSTAMP:20260527T090436Z UID:0000001923@events.thp.uni-koeln.de DESCRIPTION:Meng-Yuan Li\, SYSU\n\nTopology\, geometry & entanglement in e xactly solvable fracton models\n\nAs a new kind of topological order combi ning topology and geometry\, fracton orders have attracted attentions from various domains for its theoretical novelty and potential implication for quantum information. The mobility of particles in fracton orders is restr icted in lower dimensional subsystems of certain geometry\, which is deepl y rooted in novel entanglement patterns. In this talk\, I will introduce a series of fracton ordered exactly solvable models which include not only point-like particles but also spatially extended excitations such that bot h mobility and deformability are restricted. We construct Hamiltonians\, g round state wavefunctions and excitations\, and study several exotic prope rties such as ground state degeneracies. We establish a program of entang lement renormalization for these fixed-point wavefunctions\, rendering a h ierarchy of entanglement patterns. Finally\, I will demonstrate our explor ation on subsystem symmetry protected topological orders\, which are dual to fracton orders\, focusing on the idea of strange correlators and genera tion of subsystem symmetries via higher-order cellular automata. The talk will be ended with several future directions.\n\nContact Person: Guo-Yi Zh u / Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Sam Garratt DTSTART;TZID=Europe/Berlin:20240319T140000 DTEND;TZID=Europe/Berlin:20240319T153000 DTSTAMP:20260527T090436Z UID:0000001933@events.thp.uni-koeln.de DESCRIPTION:Sam Garratt\, UC Berkeley\n\nEfficient probes of quantum measu rement and thermalization\n\nI will discuss two problems: (i) observing me asurement-induced collective phenomena\, such as the measurement-induced e ntanglement transition\, and (ii) testing the eigenstate thermalization hy pothesis\, which forms the basis of our understanding of thermalization in isolated many-body quantum systems.\n\nIn the first case\, standard exper iments are not scalable because of the need to post-select on sets of meas urement outcomes whose probabilities are exponentially small in the number of degrees of freedom. I will show that a different approach\, which invo lves cross-correlating classical and quantum simulations\, can be used to determine both upper and lower bounds on measurement-induced entanglement. This result shows that it is possible to efficiently and unambiguously ob serve measurement-induced collective phenomena. \n\nIn the second case\, a basic issue is that the theory of thermalization in isolated many-body q uantum systems is formulated in terms of properties of eigenstates. At fin ite energy densities\, many-body level separations are exponentially small \, so in general we need exponential time to resolve eigenstates. I will s how how the quantum search algorithm can be used to construct states havin g inverse polynomial energy width\, as well as superpositions of such stat es. I will then discuss how\, using these states\, it is possible to formu late a test for violations of ETH that is valid in individual systems. Fin ally\, I will show that detecting a violation of ETH using this test is a Quantum Merlin Arthur (QMA) problem.\n\nContact Person: Guo-Yi Zhu LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Leonard Bleiziffer DTSTART;TZID=Europe/Berlin:20240419T140000 DTEND;TZID=Europe/Berlin:20240419T153000 DTSTAMP:20260527T090436Z UID:0000001968@events.thp.uni-koeln.de DESCRIPTION:Leonard Bleiziffer\, TUM/LMU München (MSc. ongoing)\n\nToward s a prototype for a topological qubit in a px + ipy superfluid of ultracol d polar NaK molecules\n\nAs first noted in [1]\, single-component fermioni c polar molecules confined to two dimensions at sufficiently low temperatu res form a topologically non-trivial px +ipy superfluid. For NaK\, the cri tical temperature is theoretically predicted to be at around 15% of the Fe rmi temperature [2] and in our lab at MPQ we can currently reach temperatu res as cold as 25%. \nIt has been proposed in [3] to use blue-detuned twee zers to potentially braid Majoranas hosted at vortex cores in the px + ipy superfluid phase and also a topological qubit read-out scheme was suggest ed specific for ultracold molecules. Using these techniques it becomes fea sible to build a prototype of a topological qubit\, apply a gate operation by braiding Majoranas and measure the state of the qubit afterwards. This would directly show the non-Abelian character of the exchange of two vort ices and thus provide a clear signature for the existence of Majoranas at their cores. \nWithin this talk I will provide a detailed description of t he experimental techniques necessary for such a prototypical topological q ubit and outline its significance\, but also the shortcomings mainly due t o the finite lifetime of the superfluid making it unfortunately not immedi ately suitable for a full topological quantum computer.\n\n[1] N. R. Coope r and G. V. Shlyapnikov\, “Stable topological superfluid phase of ultrac old polar fermionic molecules\,” vol. 103\, no. 15\, p. 155302.\n[2] F. Deng\, X.-Y. Chen\, X.-Y. Luo\, W. Zhang\, S. Yi\, and T. Shi\, “Effecti ve potential and superfluidity of microwave-shielded polar molecules\,” vol. 130\, no. 18\, p. 183001.\n[3] S. Tewari\, S. Das Sarma\, C. Nayak\, C. Zhang\, and P. Zoller\, “Quantum computation using vortices and major ana zero modes of a p x + i p y superfluid of fermionic cold atoms\,” vo l. 98\, no. 1\, p. 010506.\n\nContact Person: Matteo Rizzi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Jan Behrends DTSTART;TZID=Europe/Berlin:20240424T100000 DTEND;TZID=Europe/Berlin:20240424T113000 DTSTAMP:20260527T090436Z UID:0000001940@events.thp.uni-koeln.de DESCRIPTION:Jan Behrends\n\nSurface codes\, quantum circuits\, and entangl ement phases\n\nSurface codes\, leading candidates for quantum error corre ction (QEC) – and entanglement phases – a key notion for many-body qua ntum dynamics - have heretofore been unrelated. Here\, we establish a link between the two. We map two-dimensional (2D) surface codes under a class of incoherent or coherent errors (bit flips or uniaxial rotations) to (1+1 )D free-fermion quantum circuits via Ising models. We show that the error- correcting phase implies a topologically nontrivial area law for the circu it's 1D long-time state |ψ∞>. Above the error threshold\, we find a top ologically trivial area law for incoherent errors and logarithmic entangle ment in the coherent case. In establishing our results\, we formulate 1D p arent Hamiltonians for |ψ∞> via linking Ising models and 2D scattering networks\, the latter displaying respective insulating and metallic phases and setting the 1D fermion gap and topology via their localization length and topological invariant. We expect our results to generalize to a duali ty between the error-correcting phase of (d+1)D topological codes and d-di mensional area laws\; this can facilitate assessing code performance under various errors. The approach of combining Ising models\, scattering netwo rks\, and parent Hamiltonians can be generalized to other fermionic circui ts and may be of independent interest.\n\nContact Person: Michael Buchhold LOCATION:Seminar Room 0.03\, ETP and https://uni-koeln.zoom.us/j/977154451 24?pwd=SnRuaWFSN0lHeVQxdkU3dUVGRS8xUT09 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Catalin-Mihai Halati DTSTART;TZID=Europe/Berlin:20240426T140000 DTEND;TZID=Europe/Berlin:20240426T153000 DTSTAMP:20260527T090436Z UID:0000001939@events.thp.uni-koeln.de DESCRIPTION:Catalin-Mihai Halati\n\nProbing and Controlling Non-Equilibriu m Dynamical Phenomena in Many body Quantum systems\n\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Philippe Faist DTSTART;TZID=Europe/Berlin:20240503T140000 DTEND;TZID=Europe/Berlin:20240503T153000 DTSTAMP:20260527T090436Z UID:0000001941@events.thp.uni-koeln.de DESCRIPTION:Philippe Faist\, FU Berlin\n\nQuantum complexity in many-body physics: random circuits and thermodynamics\n\nQuantum complexity is emerg ing as a key property of many-body systems\, including black holes\, topol ogical materials\, and early quantum computers. A state's complexity quant ifies the number of computational gates required to prepare the state from a simple tensor product. I will discuss two approaches to better understa nd the role of quantum complexity in many-body physics. First\, we'll cons ider random circuits\, a model for chaotic dynamics. In such circuits\, th e quantum complexity grows linearly until it saturates at a value exponent ial in the system size. In the presence of measurements\, we observe a pha se transition in the complexity growth as a function of the rate at which measurements are performed: At low measurement rates\, the exact complexit y grows linearly up to an exponentially large value\, while at high measur ement rates\, the complexity remains low. This result is in line with a nu mber of studies\, especially in the condensed matter community\, which hav e shown phase transitions in the entanglement of the state generated by ra ndom circuits with measurements. In the second part of my talk\, I'll focu s on a first-principles approach to understanding how complexity affects t he possible processes that a many-body system can undergo. I'll introduce the complexity entropy\, a measure of entropy that accounts for an observe r's limited ability to measure complex observables\, and discuss its relev ance for the physical properties of many-body systems. I'll conclude with a number of open questions\, inviting in particular insight from the audie nce's strong condensed matter background to complement our information-the oretic approaches.\n\nContact Person: Michael Buchhold LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Sara Murciano DTSTART;TZID=Europe/Berlin:20240531T140000 DTEND;TZID=Europe/Berlin:20240531T153000 DTSTAMP:20260527T090436Z UID:0000001932@events.thp.uni-koeln.de DESCRIPTION:Sara Murciano\, Caltech\n\nQuantum criticality under imperfect teleportation\n\nThe combination of entanglement\, measurement\, and clas sical communication allows the teleportation of quantum states between dis tant parties. In this talk\, I will study the transfer of correlations and entanglement in many-body wavefunctions under imperfect teleportation pro tocols\, specifically focusing on the ground state of a critical Ising cha in. I will show that imperfections act as weak measurements on the telepor ted critical state. Leveraging the theory of measurement-altered quantum c riticality\, I can quantify the resilience of critical-state teleportation . Our findings identify classes of teleportation protocols that either mai ntain universal long-range entanglement and correlations\, weakly modify t hem\, or preserve power-law correlations while eliminating long-range enta nglement.\n\nContact Person: Guo-Yi Zhu LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Vir Bulchandani DTSTART;TZID=Europe/Berlin:20240610T130000 DTEND;TZID=Europe/Berlin:20240610T140000 DTSTAMP:20260527T090436Z UID:0000001990@events.thp.uni-koeln.de DESCRIPTION:Vir Bulchandani\n\ntba\n\n\n\nContact Person: not specified LOCATION:Seminar Room THP (old theory building) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Emanuele Tirrito DTSTART;TZID=Europe/Berlin:20240611T140000 DTEND;TZID=Europe/Berlin:20240611T153000 DTSTAMP:20260527T090436Z UID:0000001976@events.thp.uni-koeln.de DESCRIPTION:Emanuele Tirrito\, SISSA\n\nMany-body magic: from criticality to gauge theories\n\nNon-stabilizerness - also colloquially referred to as magic - is a resource for advantage in quantum computing and lies in the access to non-Clifford operations. Developing a comprehensive understandin g of how non-stabilizerness can be quantified and how it relates to other quantum resources is crucial for studying and characterizing the origin of quantum complexity. In this presentation\, I will establish a direct link between non-stabilizerness and entanglement spectrum flatness for a pure quantum state. This connection can be exploited to efficiently investigate non-stabilizerness\, even in the presence of noise. Furthermore\, I will illustrate a Monte Carlo approach applied to the probability distribution of Pauli strings to estimate non-stabilizerness\, which is quantified by t he Stabilizer Renyi Entropies (SREs). This will provide an insightful and efficient method for characterizing and analyzing the role of non-stabiliz erness in quantum many-body systems. In particular\, I will show the impor tance of magic in (a) one-dimensional systems\, where the long-range magic displays strong signatures of conformal quantum criticality (Ising\, Pott s\, and Gaussian)\, overcoming the limitations of full state magic\, (b) i n two-dimensional Z2 lattice gauge theories\, where I will show the eviden ce that magic is able to identify the confinement-deconfinement transition \, and displays critical scaling behavior even at relatively modest volume s.\n\nContact Person: Xhek Turkeshi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Neil Dowling DTSTART;TZID=Europe/Berlin:20240612T163000 DTEND;TZID=Europe/Berlin:20240612T173000 DTSTAMP:20260527T090436Z UID:0000001993@events.thp.uni-koeln.de DESCRIPTION:Neil Dowling\, Monash University\, Australia\n\nScrambling is Necessary but Not Sufficient for Chaos\n\nFast quantum information scrambl ing and non-integrability are characteristic of generic many-body systems\ , thought to underpin a number of relevant problems from thermalization of isolated systems to the black hole information paradox. Our results prove a strict separation between these two concepts. Specifically\, out-of-tim e-order correlators (OTOCs) constitute a probe for Local-Operator Entangle ment (LOE). There is strong evidence that an extensive growth of LOE is a faithful dynamical indicator of (spectral) quantum chaos\, while OTOC deca y corresponds to operator scrambling\, often conflated with chaos. I will first overview these two concepts\, before showing that rapid OTOC decay i s a necessary but not sufficient condition for linear (chaotic) growth of LOE entropy. These results are analytically supported through examples of local-circuit models of many-body dynamics\, including both integrable and non-integrable dual-unitary circuits. I will also show that this relation is optimal\; showing sufficient conditions under which dual unitary dynam ics leads to an equivalence of scrambling and chaos\, in terms of a spacet ime transfer matrix of the Floquet dynamics. Finally\, I will overview an application of these notions of many-body chaos in effecting genuinely qua ntum protections of quantum machine learning algorithms against adversaria l attacks.\n\nContact Person: Silvia Pappalardi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Thomas Barthel DTSTART;TZID=Europe/Berlin:20240614T140000 DTEND;TZID=Europe/Berlin:20240614T153000 DTSTAMP:20260527T090436Z UID:0000001989@events.thp.uni-koeln.de DESCRIPTION:Thomas Barthel\, Duke University\n\nCriticality\, phase transi tions\, and irreducibility in open quantum many-body systems\n\nIn the the rmodynamic limit\, nonequilibrium steady states of open quantum many-body systems can undergo phase transitions due to the competition of unitary an d driven-dissipative dynamics. Considering Markovian systems\, I will desc ribe recent results concerning preconditions for criticality\, phase trans itions\, and irreducibly.\n(a) A large class of translation-invariant ferm ionic and bosonic systems can be characterized almost completely -- "quadr atic" systems\, where the Hamiltonian is quadratic in the ladder operators \, and the Lindblad operators are either linear or quadratic and Hermitian [1]. In one dimension\, such systems with finite-range couplings cannot b e critical\, i.e.\, steady-state correlations necessarily decay exponentia lly. For the quasi-free case without quadratic Lindblad operators\, fermio nic systems with finite-range couplings are non-critical for any number of spatial dimensions. Quasi-free bosonic systems in d>1 dimensions can be c ritical. Furthermore\, for quadratic systems without symmetry constraints beyond particle-hole symmetries\, all gapped Liouvillians belong to the sa me phase [2]. This also has implications for transitions in non-quadratic (interacting) systems above the upper critical dimension [3].\n(b) A relat ed scenario are open systems with dynamical constraints that make it possi ble to bring the Liouvillian into block-triangular form and to assess the spectrum through suitable operator basis transformations. I will discuss c orresponding classes of systems where Weyl ordering relations establish th e absence of dissipative phase transitions [4].\n(c) Time permitting\, we can discuss the important concept of (Davies) irreducibility in driven-dis sipative systems\, i.e.\, the question whether there exist non-trivial inv ariant subspaces. Steady states of irreducible systems are unique and fait hful\, i.e.\, they have full rank. Extending seminal work by Davies\, Frig erio and others from the 1970s\, we found a powerful algebraic criterion f or irreducibility [5].\n\n[1] "Solving quasi-free and quadratic Lindblad m aster equations for open fermionic and bosonic systems"\, arXiv:2112.08344 \, J. Stat. Mech. 113101 (2022)\n[2] "Criticality and phase classification for quadratic open quantum many-body systems"\, arXiv:2204.05346\, PRL 12 9\, 120401 (2022)\n[3] "Driven-dissipative Bose-Einstein condensation and the upper critical dimension"\, arXiv:2311.13561\, PRA 109\, L021301 (2024 )\n[4] "Super-operator structures and no-go theorems for dissipative quant um phase transitions"\, arXiv:2012.05505\, PRA 105\, 052224 (2022)\n[5] "C riteria for Davies irreducibility of Markovian quantum dynamics"\, arXiv:2 310.17641\, J. Phys. A: Math. Theor. 57\, 115301 (2024)\n\nContact Person: Sebastian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Michele Filippone DTSTART;TZID=Europe/Berlin:20240621T140000 DTEND;TZID=Europe/Berlin:20240621T153000 DTSTAMP:20260527T090436Z UID:0000001977@events.thp.uni-koeln.de DESCRIPTION:Michele Filippone\, Grenoble\n\nExact Description of Transport in Quantum Stochastic Resistors and Monitored Devices\n\nUnderstanding th e emergence of diffusion in quantum systems remains a challenging problem in theoretical physics. An extended class of models expected to exhibit di ffusive behavior is given by Quantum Stochastic Hamiltonians (QSHs)\, whic h describe lattice models affected by time- and space-dependent noise. How ever\, the averaged dynamics of such models are governed by non-linear Lin dblad equations\, whose theoretical study usually relies on numerical meth ods or case-by-case solutions\, with strong constraints on geometries and driving protocols.\n\nIn this talk\, I will present a systematic method to derive exact and analytical solutions for the stationary quantum transpor t of QSHs in arbitrary configurations [1]. Our solution is based on an exa ct self-consistent Born scheme for diagrammatics in the Keldysh representa tion [2]. We show that most QSHs behave as diffusive "quantum stochastic r esistors\," whose properties are encoded in the Keldysh component of the s ingle-particle Green's function. I will provide a semi-classical interpret ation of such systems [3]\, and in particular\, I will discuss how our exa ct solution demonstrates the validity of a new perturbation scheme in the inverse system size\, named the 1/N expansion\, to study out-of-equilibriu m diffusive/ohmic systems.\n\nI will conclude by discussing how our approa ch can be extended to describe quantum transport in continuously monitored settings. I will show that measurements trigger non-reciprocal currents i n quantum devices\, thus acting as a resource for power generation and qua ntum measurement cooling [4].\n\n[1] T. Jin\, J. S. Ferreira\, M. Filippon e\, T. Giamarchi\, Physical Review Research 4\, 013109 (2022)\n[2] P. E. D olgirev\, J. Marino\, D. Sels\, E. Demler\, Physical Review B 102\, 100301 (2020)\n[3] T. Jin\, J. S. Ferreira\, M. Filippone\, T. Giamarchi\, Physi cal Review Research 5\, 013033 (2023)\n[4] J. S. Ferreira\, T. Jin\, J. Ma nnhart\, T. Giamarchi\, M. Filippone\, Physical Review Letters 132\, 13630 1 (2024) – Editors’ Suggestion\n\nContact Person: Matteo Rizzi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Jiaxin Qiao DTSTART;TZID=Europe/Berlin:20240628T140000 DTEND;TZID=Europe/Berlin:20240628T153000 DTSTAMP:20260527T090436Z UID:0000002006@events.thp.uni-koeln.de DESCRIPTION:Jiaxin Qiao\, TU Munich\n\nLattice Model of 1D Spinful U(1) To pological Superconductor: An iDMRG Study\n\nRecently\, one-dimensional top ological p-wave superconductors have attracted significant interest in the realm of topological quantum computing. Typically\, these systems involve proximity-induced superconductivity. However\, it is intriguing to explor e one-dimensional fermionic systems that conserve charge and are thus inhe rently gapless. In our study\, we begin by examining an isotropic Hamilton ian that describes spinful fermions on a 1D chain to investigate emergent superconductivity. Through large-scale infinite density matrix renormaliza tion group (iDMRG) simulations\, we identify two distinct phases: a weak c oupling phase with gapless fermion excitations and a strong coupling phase marked by gapless 4e boson excitations. We find that the correlation func tions can be accurately described by a simple two-fluid model. Furthermore \, introducing an easy-axis anisotropic interaction reveals a new pattern: a gapless symmetry-protected state emerges in the weak coupling phase\, w hile 2e superconductivity becomes possible in the strong coupling phase.\n \nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Yigal Meir DTSTART;TZID=Europe/Berlin:20240708T120000 DTEND;TZID=Europe/Berlin:20240708T133000 DTSTAMP:20260527T090436Z UID:0000002016@events.thp.uni-koeln.de DESCRIPTION:Yigal Meir\, Ben Gurion University\n\nHow to measure entropy o f exotic particles\n\n\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Yuri Minoguchi DTSTART;TZID=Europe/Berlin:20240710T160000 DTEND;TZID=Europe/Berlin:20240710T173000 DTSTAMP:20260527T090436Z UID:0000002019@events.thp.uni-koeln.de DESCRIPTION:Yuri Minoguchi\, TU Wien\n\nA Unified Interface Model for Diss ipative Transport of Bosons and Fermions\n\nWe study the directed transpor t of bosons along a one dimensional lattice in a dissipative setting\, whe re the hopping is only facilitated by coupling to a Markovian reservoir. B y combining numerical simulations with a field-theoretic analysis\, we inv estigate the current fluctuations for this process and determine its asymp totic behavior. These findings demonstrate that dissipative bosonic transp ort belongs to the KPZ universality class and therefore\, in spite of the drastic difference in the underlying particle statistics\, it features the same coarse grained behavior as the corresponding asymmetric simple exclu sion process (ASEP) for fermions. However\, crucial differences between th e two processes emerge when focusing on the full counting statistics of cu rrent fluctuations. By mapping both models to the physics of fluctuating i nterfaces\, we find that dissipative transport of bosons and fermions can be understood as surface growth and erosion processes\, respectively. With in this unified description\, both the similarities and discrepancies betw een the full counting statistics of the transport are reconciled. Beyond p urely theoretical interest\, these findings are relevant for experiments w ith cold atoms or long-lived quasi-particles in nanophotonic lattices\, wh ere such transport scenarios can be realized.\n\nContact Person: Michael B uchhold LOCATION:Seminar Room 0.02\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Alberto Nardin DTSTART;TZID=Europe/Berlin:20240712T140000 DTEND;TZID=Europe/Berlin:20240712T153000 DTSTAMP:20260527T090436Z UID:0000001991@events.thp.uni-koeln.de DESCRIPTION:Alberto Nardin\, Uni Paris Sud\n\nLinear and nonlinear edge dy namics in fractional quantum Hall systems\n\n\n\nContact Person: Matteo Ri zzi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Roman Lange DTSTART;TZID=Europe/Berlin:20240719T140000 DTEND;TZID=Europe/Berlin:20240719T153000 DTSTAMP:20260527T090436Z UID:0000002014@events.thp.uni-koeln.de DESCRIPTION:Roman Lange\n\nQuench Dynamics in Multilayer Kitaev Liquids (B achelor Kolloquim)\n\n\n\nContact Person: Aprem Joy LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Leon Wastl DTSTART;TZID=Europe/Berlin:20240820T100000 DTEND;TZID=Europe/Berlin:20240820T110000 DTSTAMP:20260527T090436Z UID:0000002023@events.thp.uni-koeln.de DESCRIPTION:Leon Wastl\, LMU Munich\n\nAdaptively Optimizing the Trotteriz ation for Digital Quantum Simulation through Reinforcement Learning\n\n\n\ nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Ram Mummadavarapu DTSTART;TZID=Europe/Berlin:20240822T100000 DTEND;TZID=Europe/Berlin:20240822T110000 DTSTAMP:20260527T090436Z UID:0000002026@events.thp.uni-koeln.de DESCRIPTION:Ram Mummadavarapu\, FZ Julich\n\ntba\n\n\n\nContact Person: Xh ek Turkeshi / Simon Trebst LOCATION:zoom END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Anish Koley DTSTART;TZID=Europe/Berlin:20240829T140000 DTEND;TZID=Europe/Berlin:20240829T153000 DTSTAMP:20260527T090436Z UID:0000002034@events.thp.uni-koeln.de DESCRIPTION:Anish Koley\, IISER Mohali (India)\n\nEffect of vacancies on J 1-J2 Heisenberg Model\n\nThe spin-1/2 nearest neighbour AFM Heisenberg mod el on square lattice is known to exhibit an exotic phase diagram depending on the J2/J1 strength. In this seminar\, I will talk about a semi-classic al approach which captures the effective quantum picture by using dimers a s proxy for quantum fluctuations.\nIn the final part I will show the chang es in the same model on introducing vacancies/holes (spin 0). It is observ ed that the intermediate spin-liquid/dimer region between Néel order and collinear AFM state gets extended on both the sides.\n\nContact Person: Ma tteo Rizzi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Joaquin Rodriguez Nieva DTSTART;TZID=Europe/Berlin:20240830T100000 DTEND;TZID=Europe/Berlin:20240830T113000 DTSTAMP:20260527T090436Z UID:0000002018@events.thp.uni-koeln.de DESCRIPTION:Joaquin Rodriguez Nieva\, Texas A&M University\n\nProbing chao s and ergodicity in programmable quantum matter\n\nA long-standing challen ge in the field of statistical mechanics has been defining notions of chao s and ergodicity in quantum regimes. For instance\, the widely-accepted de finition of quantum chaos hinges on the random matrix theory (RMT) behavio r of eigenstates. However\, the RMT description primarily captures the coa rse-grained behavior of quantum states\, e.g. their volume-law entanglemen t entropy. In this talk\, I will discuss how richer universal structures e merge when studying the fine-grained correlations---or higher statistical moments---of quantum state ensembles beyond RMT. Importantly\, such fine-g rained correlations are now measurable in programmable quantum matter---la rge-scale systems whose basic constituents can be individually controlled at the quantum level---and are quite relevant in quantum applications\, su ch as characterizing how much randomness a quantum device can generate. Fi rst\, I will show that spatial locality and energy conservation is imprint ed in the structure of eigenstate ensembles of physical (i.e.\, spatially local and finite local Hilbert space) Hamiltonian systems\, and how these features can be incorporated into RMT descriptions [1\,2]. I will also sho w that physical Hamiltonians can exhibit `maximally chaotic' behavior in w hich eigenstates are maximally entropic given the constraints of locality and energy conservation[1]. Separately\, I will show that midspectrum (or high energy) states evolving under quantum chaotic Hamiltonian dynamics\, which are typically expected to evolve into features states at late times\ , can still exhibit rich classes of universal behaviors at late times when looking at their higher statistical moments [3].\n\nReferences:\n[1] JRN\ , Jonay\, and Khemani\, PRX 14\, 031014 (2024).\n[2] Langlett and JRN\, ar xiv/2403.10600.\n[3] Ghosh\, Langlett\, Hunter-Jones\, and JRN\, to appear .\n\nContact Person: Sebastian Diehl / Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Urban Seifert DTSTART;TZID=Europe/Berlin:20240830T135000 DTEND;TZID=Europe/Berlin:20240830T144000 DTSTAMP:20260527T090436Z UID:0000002029@events.thp.uni-koeln.de DESCRIPTION:Urban Seifert\, University of Cologne\n\nMoiré lattices in sp ace and time: Engineering Quantum Matter\n\n\n\nContact Person: Achim Rosc h / Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Esther Delap DTSTART;TZID=Europe/Berlin:20240904T100000 DTEND;TZID=Europe/Berlin:20240904T113000 DTSTAMP:20260527T090436Z UID:0000002035@events.thp.uni-koeln.de DESCRIPTION:Esther Delap\n\nExploring the Houng-Ou-Mandel effect using Loc al Photons\n\n\n\nContact Person: Matteo Rizzi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Beatrice Magni DTSTART;TZID=Europe/Berlin:20240904T110000 DTEND;TZID=Europe/Berlin:20240904T120000 DTSTAMP:20260527T090436Z UID:0000002038@events.thp.uni-koeln.de DESCRIPTION:Beatrice Magni\, University of Bologna\n\nNonstabilizerness cl asses in quantum states\n\n\n\nContact Person: Dmitry Bagrets / Xhek Turke shi LOCATION:Seminar Room 0.01\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Hanh Dung Nguyen DTSTART;TZID=Europe/Berlin:20240906T140000 DTEND;TZID=Europe/Berlin:20240906T153000 DTSTAMP:20260527T090436Z UID:0000002032@events.thp.uni-koeln.de DESCRIPTION:Hanh Dung Nguyen\, FU Berlin\n\ntba\n\n\n\nContact Person: Mat teo Rizzi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Akhil Furtado DTSTART;TZID=Europe/Berlin:20240913T140000 DTEND;TZID=Europe/Berlin:20240913T153000 DTSTAMP:20260527T090436Z UID:0000002036@events.thp.uni-koeln.de DESCRIPTION:Akhil Furtado\n\nTopological phases and Edge States in an Exac tly Solvable Gamma Matrix model\n\n\n\nContact Person: Sebastian Diehl & M atteo Rizzi LOCATION:Zoom ( URL https://uni-koeln.zoom.us/j/98502673344?pwd=K5k4dLAHsK cjbKYUb9obK9HZhiAGFk.1 ) END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Damiano De Angelis DTSTART;TZID=Europe/Berlin:20240926T100000 DTEND;TZID=Europe/Berlin:20240926T113000 DTSTAMP:20260527T090436Z UID:0000002055@events.thp.uni-koeln.de DESCRIPTION:Damiano De Angelis\, LPTM - Cergy Paris\n\nStatic Complexity a nd Dynamic Ease: The XYZ Chain and Transport in HCBs\n\nThe complexity of the XYZ spin 1/2 chain captures the most generic anisotropic magnetic inte raction in a one-dimensional system. It constitutes a reference system to better understand quantum magnetism and related phenomena. Starting from t his spin chain\, defined on a discrete lattice\, we will study its sector with an odd number of sites to analyze frustration and its implications. T he standard Bethe ansatz procedure cannot be applied to the XYZ chain with an odd number of sites\, and the adapted technique shows how static syste ms may require very convoluted approaches. In the continuum limit\, the XY Z chain maps onto the famous sine-Gordon model\, but this mapping is non-t rivial. Studying the frustrated boundary condition sector of the chain wil l allow for the examination of the field theory model\, especially the beh avior of topological excitations\, known for their robustness.\n\nIn contr ast\, a much more intuitive approach emerges for studying the dynamics of a system of hard-core bosons in one dimension. Such bosonic particles\, in the impenetrability limit\, are reduced to free fermions and are thus con nected to spin chains. In the described project\, these bosons are confine d in a box\, then released and subjected to ballistic transport. For these systems\, Generalised Hydrodynamics techniques find fertile ground and ar e clear and effective. They show that an interesting phenomenon arises due to the dynamics: at finite temperatures\, in the static case\, the system is known to present exponentially decaying density-density correlations. After the quench—removing the wall and allowing the system to evolve—t hese correlations exhibit algebraic decay\, a typical feature of the groun d state. A deep numerical counterpart is provided to study the robustness of this emergence\, as well as the suitability of Quantum Generalised Hydr odynamics for the regimes involved.\n\nContact Person: Matteo Rizzi & Xhek Turkeshi LOCATION:SR 0.01 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Max McGinley DTSTART;TZID=Europe/Berlin:20241031T140000 DTEND;TZID=Europe/Berlin:20241031T160000 DTSTAMP:20260527T090436Z UID:0000002042@events.thp.uni-koeln.de DESCRIPTION:Max McGinley\, Cambridge\n\nMeasurement-induced entanglement a nd complexity in shallow 2D quantum circuits\n\nThere has been a great dea l of recent interest in understanding how measurements can influence the d ynamics of entanglement in many-body systems. In this talk\, I will discus s how long-ranged entanglement can be generated by measuring states prepar ed by constant-depth 2D quantum circuits. We introduce a new theoretical t echnique\, based on ideas from multi-user quantum Shannon theory\, which a llows us to establish a rigorous lower bound on the amount of entanglement generated by measurements in this setting. Our method avoids the so-calle d replica approach--the main tool employed for studying such problems so f ar--which gives rigorous results only in the simplest of scenarios. Using this technique\, we prove that generic (random) 2D shallow circuits produc e extensive long-ranged measurement-induced entanglement above some critic al depth\, even though the pre-measurement state is strictly short-ranged entangled. I will discuss the consequences of this result for the computat ional complexity of sampling from generic shallow-depth quantum circuits\, and for the hardness of contracting random 2D tensor networks.\n\nBased o n work with Daniel Malz and Wen Wei Ho (arXiv forthcoming)\n\nContact Pers on: Silvia Pappalardi LOCATION:215 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Ludwig Hruza DTSTART;TZID=Europe/Berlin:20241108T140000 DTEND;TZID=Europe/Berlin:20241108T160000 DTSTAMP:20260527T090436Z UID:0000002052@events.thp.uni-koeln.de DESCRIPTION:Ludwig Hruza\, ENS\n\nCharacterising the fluctuation of spatia l quantum coherence in mesoscopic disordered conductors\n\nUnderstanding t ransport in diffusive systems far away from equilibrium has been a guiding research question for many years. For classical systems we meanwhile poss es a unifying framework\, the so-called Macroscopic Fluctuation Theory\, t hat describes the large deviation statistics of density and current profil es in a universal way\, relying only on two model-dependent transport coef ficients. A natural question is if this theory can be extend to incorporat e coherent quantum effects? With this aim in mind\, the so-called Quantum Simple Symmetric Exclusion Process (QSSEP)\, a 1d model of noisy fermions\ , can serve as a microscopic toy model to study fluctuating coherent and d iffusive transport. Besides the physical motivation\, QSSEP is also intere sting for mathematicians\, since it is exactly solvable due to a connectio n with free probability.\n\nIn this talk I will focus on our recent effort to connect QSSEP to the literature on mesoscopic disordered conductors. I n particular\, we have studied numerically fluctuations of the spatial dis tribution of quantum coherence in the 3d Anderson model\, a quantity that is more of theoretical interest\, since\, to our knowledge\, it is not (ye t) experimentally accessible in diffusive conductors and for this reason h as probably not received much attention. But quite surprisingly\, the anal ytic formulae for quantum coherence in QSSEP seem match the numerical resu lts for the Anderson model to a good degree. This opens the possibility th at free probability might also be a useful tool in the description of meso scopic conductors — given\, of course\, that we are able to find an anal ytical justification for this correspondence. I will end by proposing a fe w ideas in that direction.\n\nContact Person: Silvia Pappalardi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Claudia Artiaco DTSTART;TZID=Europe/Berlin:20241129T140000 DTEND;TZID=Europe/Berlin:20241129T160000 DTSTAMP:20260527T090436Z UID:0000002071@events.thp.uni-koeln.de DESCRIPTION:Claudia Artiaco\, KTH Royal Institute of Technology\, Stockhol m\n\nMany-Body Quantum Systems: A Novel Perspective from the Information L attice\n\nDuring the time evolution of many-body quantum systems entanglem ent grows rapidly\, limiting exact simulations\nto small-scale systems and small timescales. Quantum information tends\, however\, to flow towards l arger\nscales without returning to local scales\, such that its detailed l arge-scale structure does not directly affect local\nobservables. This all ows for the removal of large-scale quantum information in a way that prese rves all local\nobservables and gives access to large-scale and large-time quantum dynamics. To this end\, in [2] we proposed\na novel approach that uses the information lattice [1] to organize quantum information into dif ferent scales\,\nallowing us to define local information and information c urrents which we employ to systematically discard long-\nrange quantum cor relations in a controlled way. The resulting algorithm\, which we refer to as local-information\ntime evolution (LITE)\, is highly versatile and sui table for investigating large-scale many-body quantum dynamics\nin both cl osed and open systems with diverse hydrodynamic behaviors.\nIn this talk\, I will introduce the information lattice and present results obtained wit h LITE for the energy\ntransport in the mixed-field Ising model and the ma gnetization transport in the XX spin chain with onsite\ndephasing\, where we accurately determine the power-law exponents and the diffusion constant s [2].\nFurthermore\, I will discuss how the information lattice can be em ployed to universally characterize generic\nmany-body quantum states and c ompute intrinsic correlation lengths [4].\nReferences:\n[1] T. Klein Kvorn ing\, L. Herviou\, and J. H. Bardarson\, Time-evolution of local informati on: Thermalization\ndynamics of local observables\, SciPost Phys. 13\, 080 (2022).\n[2] C. Artiaco\, C. Fleckenstein\, D. Aceituno Chávez\, T. Klei n Kvorning\, and J. H. Bardarson\, Efficient Large-\nScale Many-Body Quant um Dynamics via Local-Information Time Evolution\, PRX Quantum 5 (2)\, 020 352\n(2024).\n[3] K. Harkins et al.\, Nanoscale engineering and dynamical stabilization of mesoscopic spin textures\,\narXiv:2310:05635.\n[4] C. Art iaco\, T. Klein Kvorning\, D. Aceituno Chávez\, L. Herviou\, and J. H. Ba rdarson\, Universal\nCharacterization of Quantum Many-Body States through Local Information\, arXiv2410:10971.\n\nContact Person: Silvia Pappalardi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Tobias Holder DTSTART;TZID=Europe/Berlin:20241209T114500 DTEND;TZID=Europe/Berlin:20241209T124500 DTSTAMP:20260527T090436Z UID:0000002046@events.thp.uni-koeln.de DESCRIPTION:Tobias Holder\, Tel Aviv University\n\nMagnetism and supercond uctivity in rhombohedral trilayer graphene\n\nThe commensurate stacking of three graphene layers on top of each other in the sequence A-B-C creates a tunable flatband system which can sidestep many of the complications tha t twisted graphene multilayers exhibit. Indeed\, recent experiments on hig h-mobility devices were able to showcase various magnetic phases and also unconventional superconductivity in the rich phase diagram spanned by carr ier density and displacement field.\nIn this talk\, I will discuss our cur rent understanding of the flavor cascades\, superconductivity and interval ley coherent states in ABC trilayer graphene based on momentum-resolved me an field considerations\, revealing the subtle interplay of trigonal warpi ng\, isospin ordering\, incommensuration and even spin-orbit coupling. I w ill further present a possible electronic origin for the observed supercon ducting phases based on nearly critical\, finite-momentum intervalley fluc tuations. \n\n[2408.10309\,2310.03781]\n\nContact Person: Simon Trebst LOCATION:215 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Neil Dowling DTSTART;TZID=Europe/Berlin:20241220T140000 DTEND;TZID=Europe/Berlin:20241220T151500 DTSTAMP:20260527T090436Z UID:0000002093@events.thp.uni-koeln.de DESCRIPTION:Neil Dowling\, University of Cologne\n\nCapturing long-range m emory in open quantum systems with tree-geometry process tensors\n\nThe pr ocess tensor framework provides an operational approach for describing non -Markovian open quantum systems\, allowing the encoding of arbitrary multi -time observables and providing unambiguous notions of non-markovianity. T his offers advantages in areas ranging from classical simulation of open s ystems to device characterization and error mitigation. However\, for comp lex dynamics\, the computational requirements of simulating a process tens or scale poorly using standard matrix product operator techniques. After i ntroducing the process tensor framework\, I will describe our new ansatz o f process tensors based on a tensor-tree geometry\, and show that they are particularly well-suited for describing strongly correlated systems with long-range memory\, such as the paradigmatic spin-boson model. Beyond this \, leveraging 2D tensor network renormalization group methods\, I will des cribe our algorithm for deriving a process tree from an underlying Hamilto nian\, via the Feynmann-Vernon influence functional. Our work lays the fou ndation for the development of more efficient numerical techniques in the field of strongly interacting open quantum systems.\n\nContact Person: Sil via Pappalardi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Benedikt Placke DTSTART;TZID=Europe/Berlin:20250110T140000 DTEND;TZID=Europe/Berlin:20250110T151500 DTSTAMP:20260527T090436Z UID:0000002044@events.thp.uni-koeln.de DESCRIPTION:Benedikt Placke\, Oxford\n\nTopological Quantum Spin Glasses a nd its realization in quantum LDPC codes\n\nOrdered phases of matter have close connections to computation. Two prominent examples are spin glass or der\, with wide-ranging applications in machine learning and optimization\ , and topological order\, closely related to quantum error correction. Her e\, we introduce the concept of topological quantum spin glass (TQSG) orde r which marries these two notions\, exhibiting both the complex energy lan dscapes of spin glasses\, and the quantum memory and long-range entangleme nt characteristic of topologically ordered systems. We use techniques from (quantum) coding theory to show that TQSG order is the low-temperature ph ase of various quantum LDPC codes on expander graphs\, including hypergrap h and balanced product codes. En route\, we develop a quantum generalizati on of Gibbs state decompositions and prove of a bottleneck theorem for qua ntum channels\, which generalizes its well-known counterpart applying to c lassical Markov chains. Our techniques are also applicable to classical sp in glasses\, where we provide a novel proof of the shattering of the Gibbs state in a wide range of spin glass models based on classical error corre cting codes.\n\nContact Person: Simon Trebst LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Ruben Burkard DTSTART;TZID=Europe/Berlin:20250117T140000 DTEND;TZID=Europe/Berlin:20250117T151500 DTSTAMP:20260527T090436Z UID:0000002099@events.thp.uni-koeln.de DESCRIPTION:Ruben Burkard\, Uni Tübingen\n\nHigh-temperature expansion of dynamical spin correlators: Dyn-HTE\n\nCurrently\, there is a scarcity of theoretical methods to calculate dynamical correlation functions at finit e temperatures in frustrated spin systems. To address this challenge\, we extend the well- established method of high-temperature expansion to the d ynamical two-point Matsubara Green’s function\, which we calculate to hi gh order in perturbation theory. We consider Heisenberg models with one co upling constant J\, arbitrary spin length\, and without external magnetic field. We use resummation techniques to extrapolate our results to tempera tures down to about T ≈ 0.2J. Our method gives an analytical expression for the frequency dependence\, enabling analytical continuation to real fr equencies. Using the dynamical information of the Matsubara correlator\, w e aim to study spin-liquid phases with this approach in the future.\n\nCon tact Person: Urban Seifert LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Rafael Álvaro Flores Calderón DTSTART;TZID=Europe/Berlin:20250128T140000 DTEND;TZID=Europe/Berlin:20250128T151500 DTSTAMP:20260527T090436Z UID:0000002108@events.thp.uni-koeln.de DESCRIPTION:Rafael Álvaro Flores Calderón\, MPI-PKS Dresden\n\nFragile s pin liquid in three dimensions\n\nMotivated by the recent appearance of th e trillium lattice in the search for materials hosting spin liquids\, we s tudy the ground state of the classical Heisenberg model on its linegraph\, the trilline lattice. We find that this network realises the recently pro posed notion of a fragile spin liquid in three dimensions. Additionally\, we analyze the Ising case and argue for a possible Z2 quantum spin liquid phase in the corresponding quantum dimer model. Like the well-known U(1) s pin liquids\, the classical phase hosts moment fractionalisation evidenced in the diluted lattice\, but unlike these\, it exhibits exponential decay both in spin correlations and interactions between fractionalised moments . This provides the first instance of a purely short-range correlated clas sical Heisenberg spin liquid in three dimensions.\n\nContact Person: Urban Seifert LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Philipp Schmoll DTSTART;TZID=Europe/Berlin:20250131T140000 DTEND;TZID=Europe/Berlin:20250131T151500 DTSTAMP:20260527T090436Z UID:0000002122@events.thp.uni-koeln.de DESCRIPTION:Philipp Schmoll\, FU Berlin\n\nBathing in a sea of candidate q uantum spin liquids: From the gapless ruby to the gapped maple-leaf lattic e\n\nhttps://arxiv.org/abs/2407.07145\n\nContact Person: Matteo Rizzi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Nathan Lacroix DTSTART;TZID=Europe/Berlin:20250204T113000 DTEND;TZID=Europe/Berlin:20250204T124500 DTSTAMP:20260527T090436Z UID:0000002124@events.thp.uni-koeln.de DESCRIPTION:Nathan Lacroix\, ETH Zurich\n\nScaling and logic in the color code on a superconducting quantum processor\n\nQuantum error correction is essential for bridging the gap between the error rates of physical device s and the extremely low logical error rates required for quantum algorithm s. Recent error-correction demonstrations on superconducting processors ha ve focused primarily on the surface code\, which offers a high error thres hold but poses limitations for logical operations. In contrast\, the color code enables much more efficient logic\, although it requires more comple x stabilizer measurements and decoding techniques. Measuring these stabili zers in planar architectures such as superconducting qubits is challenging \, and so far\, realizations of color codes have not addressed performance scaling with code size on any platform. Here\, we present a comprehensive demonstration of the color code on a superconducting processor\, achievin g logical error suppression and performing logical operations. Scaling the code distance from three to five suppresses logical errors by a factor of Λ3/5 = 1.56(4). Simulations indicate this performance is below the thres hold of the color code\, and furthermore that the color code may be more e fficient than the surface code with modest device improvements. Using logi cal randomized benchmarking\, we find that transversal Clifford gates add an error of only 0.0027(3)\, which is substantially less than the error of an idling error correction cycle. We inject magic states\, a key resource for universal computation\, achieving fidelities exceeding 99% with post- selection (retaining about 75% of the data). Finally\, we successfully tel eport logical states between distance-three color codes using lattice surg ery\, with teleported state fidelities between 86.5(1)% and 90.7(1)%. This work establishes the color code as a compelling research direction to rea lize fault-tolerant quantum computation on superconducting processors in t he near future.\n\nContact Person: Simon Trebst / Markus Müller LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Marin Bukov DTSTART;TZID=Europe/Berlin:20250310T140000 DTEND;TZID=Europe/Berlin:20250310T150000 DTSTAMP:20260527T090436Z UID:0000002082@events.thp.uni-koeln.de DESCRIPTION:Marin Bukov\, MPI-PKS Dresden\n\nGeometric Floquet theory\n\nW e derive Floquet theory from quantum geometry. We identify quasienergy fol ding as a consequence of a broken gauge group of the adiabatic gauge poten tial U(1)↦Z. Fixing instead the gauge freedom using the parallel-transpo rt gauge uniquely decomposes Floquet dynamics into a purely geometric and a purely dynamical evolution. The dynamical average-energy operator provid es an unambiguous sorting of the quasienergy spectrum\, identifying a uniq ue Floquet ground state and suggesting a way to define the filling of Floq uet-Bloch bands. We exemplify the features of geometric Floquet theory usi ng an exactly solvable XY model and a non-integrable kicked Ising chain. W e elucidate the geometric origin of inherently nonequilibrium effects\, li ke the π-quasienergy gap in discrete time crystals or π-edge modes in an omalous Floquet topological insulators. The spectrum of the average-energy operator is a susceptible indicator for both heating and spatiotemporal s ymmetry-breaking transitions. Last but not least\, we demonstrate that the periodic lab frame Hamiltonian generates transitionless counterdiabatic d riving for Floquet eigenstates. This work directly bridges seemingly unrel ated areas of nonequilibrium physics.\n\n[1] Paul M. Schindler\, Marin Buk ov\, arXiv:2410.07029\n[2] Paul M. Schindler\, Marin Bukov\, PRL 133\, 123 402 (2024)\n\nContact Person: Simon Trebst LOCATION:PH2 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Sebastian Leontica DTSTART;TZID=Europe/Berlin:20250321T140000 DTEND;TZID=Europe/Berlin:20250321T151500 DTSTAMP:20260527T090436Z UID:0000002127@events.thp.uni-koeln.de DESCRIPTION:Sebastian Leontica\, University College London\n\nChaos of qua ntum many-body dynamics on the manifold of matrix product states\n\nFindin g suitable characterizations of quantum chaos is a major challenge in many -body physics. Many choices\, such as spectral statistics or operator grow th offered significant progress\, but not without shortcomings. There is a lways some level of ambiguity due to arbitrary thresholds in diagnostic cr iteria\, and establishing a connection to the classical notion of chaos is difficult for systems without clear classical analogues. We attempt to ov ercome this difficulty by noticing that matrix product states offer an app roximate classical description of quantum systems in 1D. The time-dependen t variational principle (TDVP) produces non-linear classical Hamiltonian d ynamics on the manifold\, allowing the direct application of traditional L yapunov spectrum based characterization of chaos. While the exact connecti on to standard quantum chaos signatures is unknown\, we prove analytical b ounds showing a deep connection between the classical Kolmogorov-Sinai ent ropy and the linear rate of entanglement growth in the system. A possible interpretation is to see local tensor fluctuations as emergent quasi-parti cles\, driven by classical dynamics. Their propagation leads to the squeez ing of wave packets on the MPS manifold\, analogous to phase-space diffusi on in classical chaotic systems\, which simultaneously drives entanglement growth following the Cardy–Calabrese mechanism. This rigorously establi shes the physical significance of the projected Lyapunov spectrum\, sugges ting it as an alternative method of characterizing chaos in quantum many-b ody systems that more closely resembles the classical chaos framework.\n\n Contact Person: Silvia Pappalardi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Gautam Nambiar DTSTART;TZID=Europe/Berlin:20250326T150000 DTEND;TZID=Europe/Berlin:20250326T161500 DTSTAMP:20260527T090436Z UID:0000002160@events.thp.uni-koeln.de DESCRIPTION:Gautam Nambiar\, University of Maryland\n\nUsing photonic corr elation functions to diagnose quantum spin liquids\n\nIn the past couple o f decades\, there have been significant advances in measuring quantum prop erties of light\, such as quadratures of squeezed light and single-photon counting. Here\, we explore whether such tools can be leveraged to probe e lectronic correlations in the many-body quantum regime. We construct a map ping from the correlators of the scattered photons to those of a correlate d insulator\, particularly for Mott insulators described by a single-band Fermi-Hubbard model at half-filling. We show that frequency filtering befo re photodetection plays a crucial role in determining this mapping. We fin d that if the ground state of the insulator is a gapped spin liquid\, a ph oton-pair correlation function\, i.e.\, $G^{(2)}$\, can detect the presenc e of anyonic excitations with fractional mutual statistics. Moreover\, we show that correlations between electromagnetic quadratures can be used to detect expectation values of static spin chirality operators on both the k agome and triangular lattices\, thus being useful in detecting chiral spin liquids. More generally\, we show that a series of hitherto unmeasured sp in-spin and spin-charge correlation functions of the material can be extra cted from photonic correlations. This work opens up access to probe correl ated materials\, beyond the linear response paradigm\, by detecting quantu m properties of scattered light.\n\nContact Person: Urban Seifert LOCATION:Zoom END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Pieter Claeys DTSTART;TZID=Europe/Berlin:20250328T140000 DTEND;TZID=Europe/Berlin:20250328T151500 DTSTAMP:20260527T090436Z UID:0000002105@events.thp.uni-koeln.de DESCRIPTION:Pieter Claeys\, MPI-PKS\n\nQuantum circuit models for free ind ependence\n\nIn chaotic many-body dynamics the relaxation of local correla tion functions to equilibrium is generally understood through the framewor k of the Eigenstate Thermalization Hypothesis (ETH). An extension of ETH t o out-of-time-order correlation functions has been recently proposed\, bas ed on the language of free probability\, in which relaxation can be unders tood as operators becoming freely independent. In this talk I will discuss a minimal model in which this approach to free independence can be unders tood as a Markovian process. These results shed light on the appearance of two-step relaxation mechanisms and generalize the influence matrix approa ch to out-of-time-order correlation functions\, and can be directly applie d to more realistic models of many-body quantum dynamics.\n\nContact Perso n: Xhek Turkeshi LOCATION:0.01 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Giacomo Gori DTSTART;TZID=Europe/Berlin:20250404T140000 DTEND;TZID=Europe/Berlin:20250404T151500 DTSTAMP:20260527T090436Z UID:0000002163@events.thp.uni-koeln.de DESCRIPTION:Giacomo Gori\, Heidelberg University\n\nForgetting boundaries: A geometric approach to confined critical systems\n\nWhat would you do if you were a system at criticality? You would of course\nforget about the m icroscopic length scales (say lattice spacing). But if you\nwere in a conf ined system you would also try to loose track of the\nboundaries. The impl ementation of above requirement in absolute geometric\nlanguage leads us t o the fractional Yamabe problem. We are looking\, within\nthe class of met rics differing from the starting flat one by a local\nrescaling factor\, f or a metric making a generalized (anomalous in physics\nvernacular) notion of curvature constant. This approach which we dub\n"Critical Geometry" le ads to novel\, testable and succesfully tested\nprediction in d>2 systems. \n\n[1] (foundation & Ising 3d) GG\, A Trombettoni [arXiv:1904.08919]\n[2] (upper critical dim) A Galvani\, GG\, A Trombettoni [arXiv:2103.12449]\n[ 3] (3d XY) A Galvani\, GG\, A Trombettoni [arXiv:2108.03488]\n[4] (3d per colation) A Galvani\, A Trombettoni\, GG [arXiv:2110.13232]\n\nContact Per son: Silvia Pappalardi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Bela Bauer DTSTART;TZID=Europe/Berlin:20250407T163000 DTEND;TZID=Europe/Berlin:20250407T174500 DTSTAMP:20260527T090436Z UID:0000002159@events.thp.uni-koeln.de DESCRIPTION:Bela Bauer\, Microsoft Quantum\n\nMajorana-Based Topological Q ubits\n\n\n\nContact Person: Simon Trebst LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Markus Müller DTSTART;TZID=Europe/Berlin:20250411T110000 DTEND;TZID=Europe/Berlin:20250411T121500 DTSTAMP:20260527T090436Z UID:0000002086@events.thp.uni-koeln.de DESCRIPTION:Markus Müller\, PSI\n\nOn the origin of quantum many-body sca rs in Rydberg blockade systems and beyond\n\nThe recent observation of sur prisingly long-lasting oscillations in the dynamics of a highly excited st ates of Rydberg atoms has attracted a lot of interest\, as they defy the e xpectation that interacting systems should thermalize very quickly. The ob served phenomena are reminiscent of “scars” that occur in quantum chao tic billiards\, where single particle eigenfunctions retain traces of peri odic classical orbits. Meanwhile a large number of models has been found t hat host one or several towers of special (non-thermal) eigenstates whose exactly equidistant eigen-energies ensure periodic\, non-thermalizing moti on.\n\nIn this talk I will discuss the unifying principles governing the s olvable models and show how the (non-solvable) Rydberg chain fits into thi s framework. I further discuss a potential connection of the special ‘sc ar’ states of Rydberg chains with single particle scars in quantum billi ards. I will show that there is a natural classical limit of the Rydberg s ystem that features unexpectedly stable periodic orbits\, that act as isla nds of parametrically suppressed chaos in the semiclassical limit. This op ens a new perspective on the limits of quantum chaoticity in the many body -context.\n\nContact Person: Silvia Pappalardi LOCATION:0.01 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Daniele Morotti DTSTART;TZID=Europe/Berlin:20250425T140000 DTEND;TZID=Europe/Berlin:20250425T151500 DTSTAMP:20260527T090436Z UID:0000002180@events.thp.uni-koeln.de DESCRIPTION:Daniele Morotti\, Padua\n\nTransport Properties of the Sachdev -Ye-Kitaev Model\n\n\n\nContact Person: Achim Rosch LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Oleksandr Sulyma DTSTART;TZID=Europe/Berlin:20250516T140000 DTEND;TZID=Europe/Berlin:20250516T153000 DTSTAMP:20260527T090436Z UID:0000002182@events.thp.uni-koeln.de DESCRIPTION:Oleksandr Sulyma\, LMU München\n\nFrom Complexity to Computab ility: Renormalised Interactions via Composite Fields\n\nQuantum correctio ns in many-body physics and general quantum field theories are captured by renormalised interactions\, or one-particle irreducible (1PI) vertices. T heir complex frequency and momentum structure makes them challenging to tr eat numerically. In this talk\, I present a unified framework based on the effective action for composite fields\, which generalises several recent and practically useful decompositions of the 4-point vertex developed in t he context of correlated electron systems. These include the frequency par ametrisation using the asymptotic classes\, the single-boson exchange deco mposition to avoid vertex divergences that appear in the parquet formalism \, and symmetric improved estimators that eliminate the need for Green’s function amputation. I demonstrate that these representations correspond to different choices of composite fields and naturally extend to more gene ral theories and any-order vertices via simple tree diagrams. This suggest s the possibility of new decompositions that could further simplify the nu merical treatment of 1PI vertices.\n\nContact Person: Fabian Kugler LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Linnea Grans-Samuelsson DTSTART;TZID=Europe/Berlin:20250523T140000 DTEND;TZID=Europe/Berlin:20250523T151500 DTSTAMP:20260527T090436Z UID:0000002158@events.thp.uni-koeln.de DESCRIPTION:Linnea Grans-Samuelsson\, University of Oxford\n\nA partition function framework for estimating logical error curves in stabilizer codes \n\nThe optimal thresholds of quantum error correcting stabilizer codes ha ve early on been related to order-disorder phase transitions within disord erered statistical mechanics models of Random Bond Ising-type. In this tal k\, I present a framework for obtaining the full logical error curves for two families of decoding strategies: maximum partition function decoders a nd probabilistic partition function decoders. Maximum likelihood (optimal) decoding is a member of the former family\, while maximum probability (MP ) decoding is a member of the latter. The logical error rates for the two families are given by two ratios of partition functions\, and estimating t he error rates through these ratios is expected to be generally more sampl e efficient than estimating the error rates by counting the number of fail ures of the corresponding decoders. Based on the distinction between the t wo decoders\, I discuss the possibility that some stabilizer codes may map to models with a maximum partition function decodability boundary that is distinct from the phase boundary. At zero temperature\, the difference be tween the two ratios measures to what degree MP decoding can be improved b y accounting for degeneracy among maximum probability errors\, through met hods such as ensembling. The presentation focuses on the example of the to ric code under uniform and non-uniform bitflip noise.\n\nContact Person: M ichael Buchhold LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Marco Cattaneo DTSTART;TZID=Europe/Berlin:20250530T140000 DTEND;TZID=Europe/Berlin:20250530T151500 DTSTAMP:20260527T090436Z UID:0000002165@events.thp.uni-koeln.de DESCRIPTION:Marco Cattaneo\, University of Helsinki\n\nThermalization is t ypical in large classical and quantum harmonic systems\n\nWe establish an analytical criterion for dynamical thermalization within harmonic systems\ , applicable to both classical and quantum models. Specifically\, we prove that thermalization of various\nobservables—such as particle energies i n physically relevant random quadratic Hamiltonians—is typical for large systems (N ≫ 1) with initial conditions drawn from the microcanonical d istribution.\nMoreover\, we show that thermalization can also arise from n on-typical initial conditions\, where only a finite fraction of the normal modes is excited. A different choice of initial conditions\, such as all the initial energy localized in a single particle\, instead leads to energ y equipartition without thermalization. Since the models we consider are i ntegrable\, our findings provide a general dynamical basis for an approach to thermalization that bypasses chaos and ergodicity\, focusing instead o n the physical requirement that thermodynamic observables depend on a larg e number of normal modes\, and build a bridge between the classical and qu antum theories of thermalization.\n\nContact Person: Silvia Pappalardi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Mingru Yang DTSTART;TZID=Europe/Berlin:20250618T140000 DTEND;TZID=Europe/Berlin:20250618T151500 DTSTAMP:20260527T090436Z UID:0000002212@events.thp.uni-koeln.de DESCRIPTION:Mingru Yang\, MPQ\n\nExtracting symmetries from tensor network states\n\nGiven a matrix product state or a projected entangled pair stat e\, how can one extract what exact or approximate symmetries it has? In th is talk\, I will answer this question partially by giving an algorithm to extract conserved charges that generate the internal continuous symmetries of the given tensor network state. Specifically\, we applied this algorit hm to 1D critical quantum spin chains and obtained the emergent lattice Ka c-Moody generators. It can also be viewed as a way to find the local integ rals of motion of an integrable model and the local parent Hamiltonian tha t can be potentially non-frustration-free. We also generalized this algori thm to 2D and found a local Hamiltonian that approximately has the RVB sta te to be its ground state.\n\n[1] Mingru Yang\, Bram Vanhecke\, and Norber t Schuch\, Phys. Rev. Lett. 131\, 036505 (2023).\n[2] Wen-Tao Xu\, Miguel Frías Pérez\, and Mingru Yang*\, in preparation.\n\nContact Person: Simo n Trebst LOCATION:0.01 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Sreemayee Aditya DTSTART;TZID=Europe/Berlin:20250620T140000 DTEND;TZID=Europe/Berlin:20250620T151500 DTSTAMP:20260527T090436Z UID:0000002208@events.thp.uni-koeln.de DESCRIPTION:Sreemayee Aditya\, University of Cologne\n\nThermalization\, s trong Hilbert space fragmentation and Irreducible strings\n\nThe advent of quantum simulators has unlocked the exploration of multiple novel ergodic ity-breaking mechanisms\, which furnish powerful tools for storing and man ipulating quantum information. This exploration recently led us to a new e rgodicity-breaking mechanism\, dubbed Hilbert space fragmentation. However \, the analytical understanding of such a fragmented Hilbert space remains quite challenging as it does not follow the conventional symmetry structu res. In this work\, we explore this mechanism in a one-dimensional correla ted hopping model utilizing an analytical construct called irreducible str ings. This construct helps us to unveil various attributes of this fragmen ted Hilbert space. Additionally\, we will discuss a novel thermalization p roperty of this fragmented quantum system\, termed “subspace-restricted thermalization”\, which impacts the static and dynamic measures of therm alization studied in this model.\n\nContact Person: Xhek Turkeshi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Victor M. Bastidas DTSTART;TZID=Europe/Berlin:20250627T140000 DTEND;TZID=Europe/Berlin:20250627T151500 DTSTAMP:20260527T090436Z UID:0000002202@events.thp.uni-koeln.de DESCRIPTION:Victor M. Bastidas\, NTT Basic Research Laboratories (Japan)\n \nSymmetry-adapted quantum algorithms for Hamiltonian simulation of many-b ody systems\n\nFrom ancient times\, symmetries have played an important ro le in our culture and even in our perception of beauty. In modern physics\ , symmetries are not only a guiding principle to build physical theories\, but they serve as a fundamental tool to predict new particles and to unif y the fundamental forces in nature [1\,2]. In the context of quantum simul ation\, symmetries can be exploited to simplify a problem and to make the simulation more efficient [3\,4]. In previous works\, however\, human effo rts are used to exploit symmetries. \nIn this talk\, I will discuss how to encode the symmetries in a quantum routine that effectively decompose the system into symmetric subspaces and allows their coherent evolution. At t he end of the quantum algorithm\, a measurement probabilistically projects the system into a desired subspace. We show applications of our approach to quantum simulation of condensed matter systems and electronic structure in chemistry. I will discuss the application of the algorithm to simulati on of the Hofstadter model.\n\n[1] A. J. Buras\, J. Ellis\, M. K. Gaillard \, and D. V. Nanopoulos\, Aspects of the grand unification of strong\, wea k and electromagnetic interactions\, Nucl. Phys. B 135\, 66 (1978).\n\n[2] S. Weinberg\, Conceptual foundations of the unified theory of weak and el ectromagnetic interactions\, Rev. Mod. Phys. 52\, 515 (1980).\n\n[3] S. M. Goodlett\, N. L. Kitzmiller\, J. M. Turney\, and H. F. Schaefer\, Molsym: A python package for handling symmetry in molecular quantum chemistry\, J . Chem. Phys. 161\, 024107 (2024).\n\n[4] P. Kratzer and J. Neugebauer\, T he basics of electronic structure theory for periodic systems\, Front. Che m. (Lausanne\, Switz.) 7\, 106 (2019).\n\n[5] V. M. Bastidas\, N. Fitzpatr ick\, K. J. Joven\, Z. M. Rossi \, S. Islam\, T. Van Voorhis \, I. L. Chua ng\, and Y. Liu\, Phys. Rev. A 111\, 052433 (2025).\n\nContact Person: Mat teo Rizzi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Bilal Hawashin DTSTART;TZID=Europe/Berlin:20250711T140000 DTEND;TZID=Europe/Berlin:20250711T151500 DTSTAMP:20260527T090436Z UID:0000002120@events.thp.uni-koeln.de DESCRIPTION:Bilal Hawashin\, Ruhr-University Bochum\n\nSpontaneous symmetr y breaking at all temperatures\n\nSpontaneous symmetry breaking can persis t at all temperatures in certain biconical O(N) x Z_2 vector models when t he underlying field theories are ultraviolet complete. So far\, the existe nce of such theories has been established in fractional dimensions for loc al but non-unitary models or in 2+1 dimensions but for non-local models. H ere\, we study local models at zero and finite temperature directly in 2+1 dimensions employing functional methods. At zero temperature\, we establi sh that our approach describes the quantum critical behavior with good acc uracy for all N ≥ 2. We then exhibit the mechanism of discrete symmetry breaking from O(N) x Z_2 -> O(N) for increasing temperature near the bicon ical critical point when N is finite but large. We calculate the correspon ding finite-temperature phase diagram and further show that the Coleman-Ho henberg-Mermin-Wagner theorem is fully respected within this approach\, i. e.\, symmetry breaking only occurs in the Z_2 sector. Finally\, we determi ne the critical N above which this phenomenon can be observed to be N_c ≈ 15\, and give an outlook for candidate theories showing similar behavi or.\n\nContact Person: Simon Trebst LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Kaito Kobayashi DTSTART;TZID=Europe/Berlin:20250804T140000 DTEND;TZID=Europe/Berlin:20250804T151500 DTSTAMP:20260527T090436Z UID:0000002225@events.thp.uni-koeln.de DESCRIPTION:Kaito Kobayashi\, University of Tokyo\n\nQuantum many-body physics meets information processing: insights from quantum r eservoir probing\n\nOver the past decade\, information-based approaches ha ve delivered fresh insights into quantum\nphenomena. In this talk\, we pus h this direction further by examining many-body physics through\nthe lens of information processing.\nThe starting point is quantum reservoir comput ing (QRC) [1\, 2]\, a quantum machine learning\nparadigm in which the natu ral dynamics of a quantum system (“quantum reservoir”) act as a\nfeatu re map for information processing. Training is limited to the classical po st-processing stage\;\nthe quantum reservoir itself remains fixed. Consequ ently\, the computational performance of QRC\nserves as a direct fingerpri nt of the underlying quantum many-body system.\nBy reversing this perspect ive\, we introduce quantum reservoir probing (QRP) [3\, 4]\, a framework\n that uses computational performance as a probe of many-body physics. We il lustrate QRP with\ntwo case studies: (i) information propagation\, where Q RP discerns distinct propagation dynamics\nreflecting the system’s inher ent nature [3]\, and (ii) quantum phase transitions\, where enhanced\ncrit ical fluctuations leave clear signatures in the computational performance [4]. These examples\nshow that QRP is a versatile tool for probi ng a wide range of exotic quantum many-body\nphenomena.\n[1] K. F ujii and K. Nakajima\, Phys. Rev. Applied 8\, 024030 (2017). \n[2] K. Koba yashi\, K. Fujii\, N. Yamamoto\, PRX Quantum 5\, 040325 (2024). \n[3] K. K obayashi and Y. Motome\, SciPost Phys. 18\, 198 (2025). \n[4] K. Kobayashi and Y. Motome\, Nat. Commun. 16\, 3871 (2025).\n\nContact Person: Yoshito Watanabe / Simon Trebst LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Mykhailo Yutushui DTSTART;TZID=Europe/Berlin:20250821T100000 DTEND;TZID=Europe/Berlin:20250821T113000 DTSTAMP:20260527T090436Z UID:0000002233@events.thp.uni-koeln.de DESCRIPTION:Mykhailo Yutushui\, Weizmann Institute of Science\n\nDaughter states and their non-Abelian parent quantum Hall phases\n\nNon-Abelian pha ses remain among the most elusive and intriguing states of matter. The fra ctional quantum Hall effect\, especially at even-denominator fillings\, pr ovides a promising platform where non-Abelian anyons may emerge. Yet\, ide ntifying the precise topological order remains a formidable challenge.\n\n In this talk\, I will introduce daughter states observed near even-denomin ator states in various materials\, including bilayer graphene and wide qua ntum wells. I will explain their origin and show how their presence serves as a diagnostic tool of the non-Abelian order of their parent states. I w ill present numerical evidence confirming the relations between the non-Ab elian parents and their corresponding daughters. I will discuss recent exp eriments that observed the daughter states and show how they offer a new\, accessible route to identifying non-Abelian phases in quantum Hall system s.\n\nContact Person: Simon Trebst LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Hiromi Ebisu DTSTART;TZID=Europe/Berlin:20250919T100000 DTEND;TZID=Europe/Berlin:20250919T113000 DTSTAMP:20260527T090436Z UID:0000002246@events.thp.uni-koeln.de DESCRIPTION:Hiromi Ebisu\, RIKEN\n\nModulated symmetries in anomalous quan tum spin systems\n\nSymmetry is one of the important guiding principles of physics\, allowing us to simplify problems in various contexts. Recently\ , there have been growing interests in updating the concept of physics\, s uch as generalized symmetry (symmetry associated with extended objects suc h as lines)\, and noninvertible symmetry. We focus on one of such new type s of symmetries\, modulated symmetry\, where symmetry operations depend on spatial coordinates (i.e.\, symmetry operations are inhomogeneous)\, orig inally invented in the context of fracton topological phases\, which are u nconventional topological phases of matter with mobility constraints. The key feature of this symmetry is that it imposes a mobility constraint on a system\, leading to intriguing physical phenomena\, such as the Hilbert s pace fragmentation\, breaking ergodicity.\nIn this talk\, we elucidate the interplay between quantum spin systems defined on two or three dimensiona l lattice with anomaly in the sense that two global symmetries exhibit non trivial commutation relation\, depending on the system size in a manner ak in to the Lieb-Schultz- Mattis type anomaly\, and modulated symmetry. We demonstrate that by gauging one of the global symmetries in an anomalous s pin model\, there exist modulated symmetries\, especially dipole symmetrie s associated with conservation of dipole. Moreover\, these modulated symme tries form unusual dipole algebra – p-form and q-form symmetry operators are related with one another via translational operators. Our considerati on provides a new insight into the emergence of modulated symmetries in a concrete quantum system on a lattice with anomaly\, making better understa nding of these exotic symmetries\, especially the ones in spatial dimensio n more than one.\nThis talk is based on a joint work with Bo Han [1] and a n upcoming work with Bo Han and Weiguang Cao [2].\n[1] H. Ebisu and B. Han \, “Noninvertible operators in one\, two\, and three dimensions via gaug ing spatially modulated symmetry\,” Phys. Rev. B 111 (Jan\, 2025) 035149 .\n[2] H. Ebisu\, B. Han\, and W. Cao\, “Modulated symmetries in anomalo us quantum spin systems (to appear)\n\nContact Person: Bo Han LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Felix Palm DTSTART;TZID=Europe/Berlin:20251010T100000 DTEND;TZID=Europe/Berlin:20251010T111500 DTSTAMP:20260527T090436Z UID:0000002242@events.thp.uni-koeln.de DESCRIPTION:Felix Palm\, Université Libre de Bruxelles\n\nQuantum Hall st ates in optical lattices: From skyrmions to hidden order\n\nThe study of i nteracting quantum Hall states and their exotic anyonic excitations poses a major challenge in current experimental and theoretical research. Quantu m simulators\, in particular cold atoms in optical lattices\, provide a pr omising platform to realize\, manipulate\, and understand such systems wit h unprecedented control. In this talk\, I will discuss how the local spin and density resolution of quantum gas microscopes extends the toolbox of q uantum Hall physics with an emphasis on spinful\, fermionic systems.\n\nFi rst\, I will discuss the interplay of spin and charge in quantum Hall stat es\, resulting in ferromagnetism and skyrmionic spin-textures [1\,2]. I wi ll show how different types of interactions lead to the stability of diffe rent classes of states and will present experimentally relevant signatures to identify these states.\n\nThen\, I will turn towards a fundamental que stion regarding the topological order of quantum Hall states: the speculat ed condensation of composite bosons exhibiting quasi long-range order. I w ill exemplify this mechanism in fermionic [2] and bosonic [3] systems and touch upon its detectability in tensor network simulations and quantum gas microscopes.\n\n[1] Palm et al.\, Ferromagnetism and skyrmions in the Hof stadter–Fermi–Hubbard model\; NJP 25 (2023)\n\n[2] Pauw et al.\, From hidden order to skyrmions: Quantum Hall states in an extended Hofstadter-F ermi-Hubbard model\; arXiv:2509.12184 (2025)\n\n[3] Pauw et al.\, Detectin g Hidden Order in Fractional Chern Insulators\; PRR 6 (2024)\n\nContact Pe rson: Matteo Rizzi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Amirreza Negari DTSTART;TZID=Europe/Berlin:20251111T140000 DTEND;TZID=Europe/Berlin:20251111T151500 DTSTAMP:20260527T090436Z UID:0000002286@events.thp.uni-koeln.de DESCRIPTION:Amirreza Negari\, Perimeter Institute\n\nCritical Mixed-State Phases from Coherent Errors: CMI\, Loop Constraints\, and Network Conducta nce\n\nCriticality in quantum many-body systems is usually tied to scale-i nvariant correlations in pure states\; mixed states lack a comparable orga nizing principle. Here we introduce critical mixed-state phases\, in which the conditional mutual information (CMI) decays with a diverging length s cale across the entire phase. We realize two such phases by applying coher ent (invertible) noise to topological memories : (i) a classical memory su bjected to coherent Pauli shuffle noise\, where we analytically establish critical CMI scaling via a statistical-mechanical mapping\; and (ii) a qua ntum memory (surface code) subjected to coherent Z rotations\, where large -scale numerics reveal a stable phase with divergent Markov length and lon g-range entanglement. A unified picture emerges by mapping CMI to transpor t physics and the conductance of a Chalker-Coddington network\, identifyin g the critical phase with a metallic regime. We further discuss implicatio ns for error correction: the critical phase is information-theoretically c orrectable yet admits no finite-depth local decoder\, whereas local decode rs exist away from criticality.\n\nContact Person: Simon Trebst LOCATION:Zoom END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Xinyu Sun DTSTART;TZID=Europe/Berlin:20251113T100000 DTEND;TZID=Europe/Berlin:20251113T110000 DTSTAMP:20260527T090436Z UID:0000002288@events.thp.uni-koeln.de DESCRIPTION:Xinyu Sun\, Tsinghua University\n\nBoundary CFTs and Holograph ic Duality: Boundary Phase Transitions and Conformal Data\n\nConformal fie ld theories (CFTs) capture universal features of critical and gapless syst ems through compact conformal data—scaling dimensions and OPE coefficien ts. Introducing a boundary or defect preserves a subgroup of conformal sym metry and enriches this data via boundary primaries and the boundary opera tor expansion (BOE). In this talk I survey boundary CFTs (BCFTs) and their holographic duals with an emphasis on phase transitions and conformal dat a. I will (i) present results on boundary criticality\, including the nove l extraordinary transition in the tricritical O(N) model\, which is the fi rst nontrivial example of spontaneous continuous symmetry breaking confine d to a two-dimensional boundary\; (ii) discuss analytic bootstrap for BCFT s with interacting boundaries\, including nonunitary-boundary CFTs that we re previously inaccessible to conformal bootstrap\; and (iii) briefly intr oduce our AdS/BCFT results\, showing how weak measurements in QFT creates an interface brane in the dual geometry\, and if time allows\, how boundar y condition changing operators and cusps can be characterized by corners o n the interface branes in a general DCFT. Taken together\, these threads p rovide an overview of novel phase transitions and structures in BCFTs and clarify the role of AdS/CFT duality in understanding the properties of bou ndaries and defects in CFTs.\n\nContact Person: Simon Trebst LOCATION:Zoom END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Zack Weinstein DTSTART;TZID=Europe/Berlin:20251117T100000 DTEND;TZID=Europe/Berlin:20251117T110000 DTSTAMP:20260527T090436Z UID:0000002291@events.thp.uni-koeln.de DESCRIPTION:Zack Weinstein\, Caltech\n\nQuantum Error Correction in Nearly Critical Toric Codes\n\nWe investigate the protection and recovery of qua ntum information stored in the ground-state manifold of deformed toric cod es\, particularly as they are pushed towards a quantum critical point. Our focus is on the toric code perturbed by transverse and longitudinal field s\, whose ground states are described by the three-dimensional classical F radkin-Shenker model via the quantum-classical mapping. Using an effective replica field theory approach in the vicinity of the topological-to-trivi al phase transition\, we show quite generally that the intrinsic error thr eshold for local Pauli decoherence remains finite as the critical point is approached. Moreover\, we demonstrate that this class of nonstabilizer co des can be simply and efficiently decoded by measuring the stabilizers of the unperturbed model. This property follows from the stoquastic nature of the deformed toric code Hamiltonians\, which in turn allows us to formula te an optimal decoder for the postmeasurement states in terms of a constra ined three-dimensional statistical physics model. We numerically implement the optimal decoder for the transverse-field toric code subjected to bit- flip decoherence and stabilizer measurements\, and we find that the error threshold for this decoder remains finite throughout the topological phase .\n\nContact Person: Simon Trebst LOCATION:0.02 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Nina del Ser DTSTART;TZID=Europe/Berlin:20251205T150000 DTEND;TZID=Europe/Berlin:20251205T161500 DTSTAMP:20260527T090436Z UID:0000002312@events.thp.uni-koeln.de DESCRIPTION:Nina del Ser\, Caltech\n\nUltrafast Non-Dispersive Flux-Driven Readout of a Fluxonium Qubit\n\n\n\nContact Person: Achim Rosch LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Maxime Debertolis DTSTART;TZID=Europe/Berlin:20251212T140000 DTEND;TZID=Europe/Berlin:20251212T153000 DTSTAMP:20260527T090436Z UID:0000002315@events.thp.uni-koeln.de DESCRIPTION:Maxime Debertolis\, Universität Bonn\n\nFew-body structures o f Quantum impurity problems in the Heisenberg picture\n\nQuantum impurity problems are known to exhibit a compact representation of their ground sta te or for quench protocols when an optimized single-particle basis is chos en. This work extends the study of single-particle rotations taylored to o perators in the Heisenberg picture. We present the concept of natural supe r-orbitals for many-body operators\, defined as the eigenvectors of the on e-body super-density matrix associated with a vectorized operator. These o bjects are related to measures of non-Gaussianity of operators associated to the occupations of the natural super-orbitals. We perform a numerical i nvestigation of the natural super-orbitals corresponding to both the time- evolution operator and a time-evolved local operator in the t-V model and in a quantum impurity model using tensor network simulations. In the quant um impurity model\, occupations of the natural orbitals for both operators decay exponentially at all times. More surprisingly\, the non-Gaussianity of the local operator saturates in time. This indicates that only a small number of orbitals contribute significantly “many-body-ness” of the o perator\, enabling a compact matrix-product-operator representation. This framework opens the door to future research that leverages the compressed structure of operators in their natural super-orbital basis to perform eff icient time evolution of operators whose non-Gaussianity is low and struct ured.\n\nContact Person: Neil Dowling LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Nele Callebaut DTSTART;TZID=Europe/Berlin:20251215T160000 DTEND;TZID=Europe/Berlin:20251215T170000 DTSTAMP:20260527T090436Z UID:0000002292@events.thp.uni-koeln.de DESCRIPTION:Nele Callebaut\, Uni Köln\n\nDissecting AdS3 gravity\n\nWe ma ke use of well-known deformations of CFT to formulate a general braneworld holography dictionary in AdS$_3$ gravity. This involves 'dissecting' AdS3 gravity\, by which we mean rewriting the Dirichlet boundary condition pro blem in terms of the boundary Weyl mode\, which is relevant for discussion s of both the Neumann boundary condition as well as Conformal boundary con dition problem. Both are important in the context of generalizing holograp hic dualities beyond standard AdS/CFT. Braneworld holography\, in particul ar\, is important in the design of set-ups that resolve the black hole inf ormation paradox using holographic entanglement.\n\nContact Person: Sebast ian Diehl\, Simon Trebst LOCATION:OTHER END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Moshe Rozali DTSTART;TZID=Europe/Berlin:20251215T140000 DTEND;TZID=Europe/Berlin:20251215T150000 DTSTAMP:20260527T090436Z UID:0000002295@events.thp.uni-koeln.de DESCRIPTION:Moshe Rozali\, University of British Columbia\, Vancouver\n\nQ uantum chaos in two-dimensional CFTs\n\nWe describe attempts to quantify t he statistics of scaling dimensions in two-dimensional conformal field the ories of large central charge. This exemplifies the influence of locality and spacetime symmetries on quantum chaotic concepts as applied to continu um quantum field theories. We comment on the relation to three dimensional gravity.\n\nContact Person: Sebastian Diehl\, Simon Trebst LOCATION:OTHER END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Julian Sonner DTSTART;TZID=Europe/Berlin:20251215T170000 DTEND;TZID=Europe/Berlin:20251215T180000 DTSTAMP:20260527T090436Z UID:0000002296@events.thp.uni-koeln.de DESCRIPTION:Julian Sonner\, University of Geneva\n\nQuantum chaos and thre e-dimensional gravity\n\n\n\nContact Person: Sebastian Diehl\, Simon Trebs t LOCATION:OTHER END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Jens Eisert DTSTART;TZID=Europe/Berlin:20251215T100000 DTEND;TZID=Europe/Berlin:20251215T110000 DTSTAMP:20260527T090436Z UID:0000002298@events.thp.uni-koeln.de DESCRIPTION:Jens Eisert\, Free University Berlin\n\nEntanglement\, informa tion and complexity in quantum systems\n\nIn this talk\, we revisit the no tions of entanglement\, information\, and\ncomplexity in quantum systems f rom a somewhat unconventional perspective —\nby placing the observer of a phenomenon at the center and adopting a\nstrictly operational viewpoint. We begin by examining the precise ways in\nwhich entanglement and complex ity in random quantum circuits are connected\n[1–3]. Along the way\, we discuss random tensor networks as a powerful tool\nfor advancing our under standing of complex quantum systems [4]. We show\nthat the average-case ti me evolution of interacting quantum systems can\, in\na well-defined sense to be explained\, be surprisingly uncomplex — despite\nthe fact that ti me evolution under local Hamiltonians is BQP-complete [5].\nBuilding on th is\, we demonstrate that entanglement theory is fundamentally\naltered onc e one accepts that all implemented operations must be both\ncomputationall y and sample efficient [6]. Pushing the operational\nperspective further\, we reveal that certain systems are not quantum\nchaotic\, even though no polynomially bounded observer can distinguish them\nfrom Gaussian unitary ensembles\, which paradigmatically represent\nquantum-chaotic systems [7]. We conclude by reflecting on the role of the\nobserver — who gathers da ta and acts operationally efficiently — in shaping\nour understanding of entanglement\, information\, and complexity.\n\n[1] Nature Physics 18\, 5 28 (2022).\n[2] Physical Review Letters 127\, 020501 (2021).\n[3] PRX Quan tum 6\, 010346 (2025).\n[4] arXiv:2508.16570 (2025).\n[5] Nature Physics 2 0\, 1401 (2024).\n[6] Nature Physics\, online (2025).\n[7] arXiv:2410.1819 6 (2024).\n\nContact Person: Sebastian Diehl\, Simon Trebst LOCATION:OTHER END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Dmitry Bagrets DTSTART;TZID=Europe/Berlin:20251215T110000 DTEND;TZID=Europe/Berlin:20251215T120000 DTSTAMP:20260527T090436Z UID:0000002299@events.thp.uni-koeln.de DESCRIPTION:Dmitry Bagrets\, FZ Jülich\n\n(Non-)adiabatic braiding protoc ol for Majorana fermions\n\nThe search for elusive Majorana fermions in so lid-state devices has occupied the scientific community for more than a de cade. Their unambiguous detection is expected to rely on a braiding protoc ol that can verify their non-Abelian statistics. We have emulated such a p rotocol using digital quantum simulations on the IBM_Brisbane quantum proc essor. Remarkably\, only 12 Trotter steps are sufficient to reproduce the theoretically predicted braiding gate with a fidelity of up to 99.9% in th e absence of decoherence and noise. In experiment\, this upper bound is re duced due to the lack of topological protection for the simulated Majorana s. However\, we show that applying advanced error-mitigation techniques ca n restore experimental fidelity to values close to the ideal limit.\n\nIn cooperation with S. Schmitz\, K. Lively\, T. Bode and B. Fauseweh\n\nConta ct Person: Sebastian Diehl\, Simon Trebst LOCATION:OTHER END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Matthew Foster DTSTART;TZID=Europe/Berlin:20251216T110000 DTEND;TZID=Europe/Berlin:20251216T120000 DTSTAMP:20260527T090436Z UID:0000002289@events.thp.uni-koeln.de DESCRIPTION:Matthew Foster\, Rice University\n\nBroken golden rules and to rtured sigma models: Monitored dynamics of interacting fermions\n\nNon-equ ilibrium quantum many-body physics is in general very poorly understood. I will talk about recent developments understanding a new class of purely q uantum particle dynamics with completely trivial kinetics. This is the phy sics of interacting fermions\, monitored by external measurements. Inspire d by previous work in the contexts of both random quantum circuits and mon itored free-fermion dynamics\, we use non-equilibrium field theory to craf t a framework to detect phase transitions in the entanglement for such a s ystem. The theory takes a form that is very similar to the single-particle theory of Anderson localization: a replicated nonlinear sigma model. I wi ll explain how interactions introduce anisotropy in the geometry of the si gma model. The most prominent part is a "mass term" that we identify with the Fermi's golden rule of rate density of particle scattering. Such a rat e density should vanish in the "area-law" phase\, where entanglement is su ppressed by the measurements. Our framework allows us to draw important im plications from this for the nature of the entanglement phase transition. I will summarize how the analysis can be applied to different Altland-Zirn bauer classes of monitored dynamics\, and how the "shape" of the entanglem ent transition might be studied from the point of view of Ricci flow on th e sigma model manifold.\n\nContact Person: Sebastian Diehl\, Simon Trebst LOCATION:OTHER END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Alex Kamenev DTSTART;TZID=Europe/Berlin:20251216T140000 DTEND;TZID=Europe/Berlin:20251216T150000 DTSTAMP:20260527T090436Z UID:0000002290@events.thp.uni-koeln.de DESCRIPTION:Alex Kamenev\, University of Minnesota\n\nPopulation Dynamics of Schroedinger Cats\n\nClassical population dynamics models exhibit a con tinuous phase transition between an extinct (absorbing) state and a state with a finite population. The most common and robust universality class of such transitions is known as directed percolation (DP). In this talk I' ll argue that there is a natural and well-defined way to generalize popula tion models to allow for coherent superpositions \nof live and dead creatu res - i.e. Schrodinger cats. Such quantum populations may also undergo tra nsitions between dead and live states\, which belong to a distinct univers ality class -- quanum DP. I will discuss a field theory of QDP\, its epsil on-expansion treatment and its possible applications to qubit arrays.\n\nC ontact Person: Sebastian Diehl\, Simon Trebst LOCATION:OTHER END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Tobias Micklitz DTSTART;TZID=Europe/Berlin:20251216T130000 DTEND;TZID=Europe/Berlin:20251216T140000 DTSTAMP:20260527T090436Z UID:0000002294@events.thp.uni-koeln.de DESCRIPTION:Tobias Micklitz\, CBPF Rio de Janeiro\n\nPath integral approac h to quantum thermalization\n\nWe discuss a real-time path-integral framew ork for capturing the unitary dynamics of chaotic many-body quantum system s that effectively act as their own environment. Extending the field theor y of chaotic or disordered single-particle systems to the many-body regime \, this approach describes a broad class of systems and disorder models be yond perturbation theory in inverse Hilbert space dimension. It offers a m icroscopic and non-perturbative account of thermalization dynamics across all relevant timescales: from initial short-time scattering processes\, th rough the onset of ergodicity at an effective Thouless time\, and up to th e many-body Heisenberg time. Applied to systems such as random circuit net works\, the theory captures the dynamical buildup of both entanglement and entropy\, providing a unified description of the crossover from initial p roduct states to fully ergodic\, maximum-entropy states.\n\nContact Person : Sebastian Diehl\, Simon Trebst LOCATION:OTHER END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Carolin Wille DTSTART;TZID=Europe/Berlin:20251216T100000 DTEND;TZID=Europe/Berlin:20251216T110000 DTSTAMP:20260527T090436Z UID:0000002297@events.thp.uni-koeln.de DESCRIPTION:Carolin Wille\, University of Oxford\n\nFrom Circuits to Fermi ons: Insights into Quantum Complexity from Tensor Networks\n\nThis talk ex plores how concepts from interacting fermionic systems can inform our unde rstanding of quantum circuit simulation. By expressing parity-preserving c ircuits as fermionic tensor networks\, we obtain a controlled expansion th at captures non-Gaussian effects and clarifies the origins of computationa l hardness.\n\nContact Person: Sebastian Diehl\, Simon Trebst LOCATION:OTHER END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Yumin Hu DTSTART;TZID=Europe/Berlin:20260116T140000 DTEND;TZID=Europe/Berlin:20260116T151500 DTSTAMP:20260527T090436Z UID:0000002301@events.thp.uni-koeln.de DESCRIPTION:Yumin Hu\, Max Planck Institute for the Physics of Complex Sys tems\, Dresden\n\nNovel steady states in dissipative many-body systems\n\n The Lindblad master equation provides a fundamental framework for describi ng\nopen quantum many-body systems coupled to a Markovian environment. Dis sipative\ncouplings not only enable the preparation and control of novel q uantum states but also lead\nto nonequilibrium phases without Hermitian co unterparts. In this talk\, I will present our two\nrecent developments in this direction. In the first part\, I will introduce the notion of asympto tic\nexceptional steady states in dissipative dynamics [1]. Although excep tional points are\nforbidden for exact degenerate steady states of Liouvil lians\, a large class of open many-body\nsystems can asymptotically approa ch an exceptional steady state as the system size increases.\nSuch an asym ptotic structure has an intriguing connection to the computational complex ity\nof dissipative state preparation. In the second part\, I will discuss a dissipative quantum link\nmodel that naturally exhibits a many-body non -Hermitian skin effect — an anomalous\nboundary localization phenomenon [2]. Despite the complexity arising from strong\ninteractions\, local gaug e symmetry enables the exact construction of steady states. We also\npropo se a hierarchical skin effect\, where different subsystems exhibit boundar y accumulation\nof multipole moments of different orders. These results de monstrate how dissipation can be\nused in quantum many-body experiments to engineer unexpected steady states.\n[1] Y.-M. Hu and J. C. Budich\, Phys. Rev. Lett. 135\, 250402 (2025).\n[2] Y.-M. Hu\, Z. Wang\, B. Lian\, and Z . Wang. Phys. Rev. Lett. 135\, 260401 (2025).\n\nContact Person: Bo Han LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Sanghyun Park DTSTART;TZID=Europe/Berlin:20260130T140000 DTEND;TZID=Europe/Berlin:20260130T151500 DTSTAMP:20260527T090436Z UID:0000002235@events.thp.uni-koeln.de DESCRIPTION:Sanghyun Park\, Seoul National University\n\nKondo screening i n the multiorbital Hubbard models and the two-channel spin-orbital Kondo m odel\n\nIn this talk\, we highlight the role of Kondo screening in strongl y correlated many-body physics. First\, we investigate the Mott transition in multiorbital Hubbard models with Hund’s coupling\, using dynamical m ean-field theory (DMFT) with the numerical renormalization group (NRG) imp urity solver. We show that the quasiparticle weight vanishes continuously or exhibits a discontinuous jump at zero temperature\, depending on the de generacy of the local ground state. We interpret this behavior in terms of Kondo screening of the effective impurity. We also identify the unstable DMFT branch as a Fermi liquid and connect it to quantum-critical scaling. Second\, we revisit the two-channel spin-orbital Kondo (2soK) model and it s anisotropic extensions. Combining NRG with analytical arguments\, we unc over previously overlooked non-Fermi-liquid fixed points in the 2soK model .\n\nContact Person: Fabian Kugler LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Zhanyu Ma DTSTART;TZID=Europe/Berlin:20260206T140000 DTEND;TZID=Europe/Berlin:20260206T151500 DTSTAMP:20260527T090436Z UID:0000002316@events.thp.uni-koeln.de DESCRIPTION:Zhanyu Ma\, Tel Aviv University\n\nEngineering the localizatio n transition in a Charge-Kondo circuit\n\nCharge Kondo circuits consist of metallic islands connected by single-mode quantum point contacts\n(QPCs). The island’s charging energy makes these circuits tunable quantum simul ators of\nvarious strongly interacting models. Here we propose a circuit t hat realizes the Kondo effect with\neffective Luttinger-liquid interaction s\, and show that it undergoes a localization transition in which\nthe QPC transmission is fully suppressed below a critical value. Experimental sig natures include\na diverging charge susceptibility and an entropy step. Ou r findings open a path toward realizing\nlocalization transitions in more exotic settings.\n\nContact Person: Fabian Kugler LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Mark Potts DTSTART;TZID=Europe/Berlin:20260327T140000 DTEND;TZID=Europe/Berlin:20260327T151500 DTSTAMP:20260527T090436Z UID:0000002355@events.thp.uni-koeln.de DESCRIPTION:Mark Potts\, MPI-PKS Dresden\n\nSpin-Qubit Noise Spectroscopy of Magnetic Berezinskii-Kosterlitz-Thouless Physics\n\nWe propose using sp in-qubit noise magnetometry to probe dynamical signatures of\nmagnetic Ber ezinskii-Kosterlitz-Thouless (BKT) physics. For a nitrogen-vacancy (NV) ce nter coupled\nto two-dimensional XY magnets\, we predict distinctive featu res in the magnetic noise spectral density\nin the sub-MHz to GHz frequenc y range. In the quasi-long-range ordered phase\, the spectrum\nexhibits a temperature-dependent power law characteristic of algebraic spin correlati ons. Above the\ntransition\, the noise reflects the proliferation of free vortices and enables quantitative extraction\nof the vortex conductivity\, a key parameter of vortex transport. These results highlight NV as a\npow erful spectroscopic method to resolve magnetic dynamics in the mesoscopic and low-frequency\nregimes and to probe exotic magnetic phase transitions. \n\nContact Person: Urban Seifert LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Felizia Braun DTSTART;TZID=Europe/Berlin:20260428T120000 DTEND;TZID=Europe/Berlin:20260428T131500 DTSTAMP:20260527T090436Z UID:0000002391@events.thp.uni-koeln.de DESCRIPTION:Felizia Braun\, TU Munich\n\nSimulation of Symmetry Protected Topological Phases on Quantum Processors\n\n\n\nContact Person: Simon Treb st LOCATION:215 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Hans Singh DTSTART;TZID=Europe/Berlin:20260430T150000 DTEND;TZID=Europe/Berlin:20260430T160000 DTSTAMP:20260527T090436Z UID:0000002394@events.thp.uni-koeln.de DESCRIPTION:Hans Singh\, MPI PKS Dresden\n\nZero noise extrapolations of t ransport coefficients\n\nSystematically increasing noise in a many body qu antum system has recently been appreciated in experiments and theory as a useful and simple method to understand properties of the noiseless system. Typically these so-called zero noise extrapolation (ZNE) schemes involve increasing noise in a system\, evaluating observables at each value of noi se and then extrapolating this data set to zero noise. In practice these s chemes work surprisingly well despite having little theoretical guarantees of success in the presence of generic noise. However using ZNE presents a n issue when extracting transport properties because—strictly speaking —no transport occurs at any non-zero noise strength since generic noise breaks any underlying conservation laws. In this talk\, I will show how ZN E can still be used to extract transport properties\, highlight when it ca n fail\, and argue that\, when successful\, the noise dependence also cont ains additional universal information about transport.\n\nContact Person: Silvia Pappalardi LOCATION:0.02 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Weiguang Cao DTSTART;TZID=Europe/Berlin:20260515T140000 DTEND;TZID=Europe/Berlin:20260515T153000 DTSTAMP:20260527T090436Z UID:0000002392@events.thp.uni-koeln.de DESCRIPTION:Weiguang Cao\, University of Southern Denmark\n\nGeneralized s ymmetries and their application in topological phases of matter\n\nRecentl y\, the notion of symmetry has been generalized\, including high form\, su bsystem\, and noninvertible symmetries. These novel symmetries have extend ed our understanding of topological phases of matter. In this talk\, I wil l review the recent development on generalized symmetry\, with a focus on noninvertible symmetry and the phases protected by it. I will present a ge neral method to classy a broad class of noninvertible symmetry protected t opological phases (NISPTs)\, together with concrete lattice realizations.\ n\nContact Person: Bo Han LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Rushikesh Patil DTSTART;TZID=Europe/Berlin:20260612T140000 DTEND;TZID=Europe/Berlin:20260612T151500 DTSTAMP:20260527T090436Z UID:0000002417@events.thp.uni-koeln.de DESCRIPTION:Rushikesh Patil\, UC Santa Barbara\n\nTo be announced\n\n\n\nC ontact Person: Simon Trebst LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Zala Lenarčič DTSTART;TZID=Europe/Berlin:20260619T140000 DTEND;TZID=Europe/Berlin:20260619T151500 DTSTAMP:20260527T090436Z UID:0000002407@events.thp.uni-koeln.de DESCRIPTION:Zala Lenarčič\, University of Ljubljana\n\nQuantum Mpemba ef fect and non-equilibrium superconductivity in weakly driven systems\n\n\n\ nContact Person: Achim Rosch LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Sebastian Paeckel DTSTART;TZID=Europe/Berlin:20260626T140000 DTEND;TZID=Europe/Berlin:20260626T151500 DTSTAMP:20260527T090436Z UID:0000002419@events.thp.uni-koeln.de DESCRIPTION:Sebastian Paeckel\, LMU\n\nSpectral Decomposition and High-Acc uracy Green’s Functions via Complex-time Krylov Expansion\n\nThe accurat e computation of low-energy spectra of strongly correlated quantum many-bo dy systems\, typically accessed via Green’s functions\, is a long-standi ng problem posing enormous challenges to numerical methods. When the spect ral decomposition is obtained from Fourier transforming a time series\, th e Nyquist-Shannon theorem limits the frequency resolution $$\\Delta \\omeg a$ according to the numerically accessible time domain size T via $\\Delta \\omega = 2 \\pi / T$. In tensor network methods\, increasing the domain size is exponentially hard due to the ubiquitous spread of correlations\, limiting the frequency resolution and thereby restricting this ansatz clas s mostly to one-dimensional systems with small quasiparticle velocities. H ere\, we show how this limitation can be overcome by augmenting the time s eries with complex-time Krylov states. With the example of the critical $S =1/2$ Heisenberg model and light bipolarons in the two-dimensional Su-Schr ieffer-Heeger model\, we demonstrate the enormous improvements in accuracy \, which can be achieved using this method.\n\nPRL 136\, 160401 (2026)\n\n Contact Person: Matteo Rizzi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:CMT | Rodrigo Pereira DTSTART;TZID=Europe/Berlin:20260717T140000 DTEND;TZID=Europe/Berlin:20260717T151500 DTSTAMP:20260527T090436Z UID:0000002411@events.thp.uni-koeln.de DESCRIPTION:Rodrigo Pereira\, International Institute of Physics\, Natal\n \nTo be announced\n\n\n\nContact Person: Simon Trebst LOCATION:0.03 END:VEVENT END:VCALENDAR