BEGIN:VCALENDAR PRODID:University of Cologne\, ITP\, Events Server X-WR-TIMEZONE:Europe/Berlin BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. Bernd Rosenow DTSTART;TZID=Europe/Berlin:20101119T164500 DTEND;TZID=Europe/Berlin:20101119T173000 DTSTAMP:20260527T090436Z UID:0000000011@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. Bernd Rosenow\, University of Leipzig\n\nSpectroscop y of Majorana fermions in non-linear transport\n\nMuch effort has been dev oted recently to the search for experimental demonstrations of Majorana fe rmions and the exotic quantum statistics that can be encoded by them. In t his talk I will mainly focus on Majorana fermions in the non-abelian quant um Hall state at filling fraction nu=5/2. To detect them\, there have been several proposals for transport experiments in the linear regime\, which however are not robust with respect to disorder in realistic samples.  I will discuss signatures of Majorana states in non-linear transport through a Coulomb blockaded antidot of nu=5/2 quantum Hall fluid surrounded by an integer quantum Hall state.  In contrast with linear Coulomb blockade (C B)\, current-voltage characteristics in the non-linear regime of the CB ho ld information of the many-particle excitation spectrum of the system. A p eak in the differential conductance dI/dV will appear whenever a proper re sonance condition between the source-drain voltage and the excitations of the dot is met. The "diamond structure" that characterizes the CB out of t he linear response regime could serve to identify the nature of the nu=5/2 state.\n\n\nContact Person: not specified LOCATION:Seminar Room ITP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. B. Trauzettel DTSTART;TZID=Europe/Berlin:20101126T163000 DTEND;TZID=Europe/Berlin:20101126T173000 DTSTAMP:20260527T090436Z UID:0000000015@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. B. Trauzettel\, Universität Würzburg\n\nDirac Ferm ions in Graphene and Topological Insulators\n\nThe carbon atoms in graphen e (Nobel Prize in Physics 2010) form a honeycomb lattice which gives rise to many of the peculiar physical properties of this fascinating material. Dictated by the interaction with the ions of the lattice\, the low energy electrons in graphene have the same dispersion relation as mass-less Dirac fermions. We will discuss interesting physical phenomena of Dirac fermion s in graphene such as Klein tunneling\, transport through evanescent modes \, and consequences of the spectrum on quantum computing devices based on graphene quantum dots.\nFurthermore\, we will address another in some sens e even richer condensed matter system that shows Dirac fermion physics: To pological insulators (TIs) behave like usual insulators in the bulk but li ke metals at the boundaries. This gives rise to Dirac fermions at the edge of a TI. In nature\, TIs have been first realized in HgTe/CdTe quantum we lls (in 2D) and later on also in 3D in BiSb\, BiSe\, as well as BiTe cryst als. We will discuss interesting physical properties of 2D TIs where spin and charge properties of the system are ultimately locked to each other.\n \nContact Person: not specified LOCATION:Seminar Room ITP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. Karyn Le Hur DTSTART;TZID=Europe/Berlin:20101210T164500 DTEND;TZID=Europe/Berlin:20101210T173000 DTSTAMP:20260527T090436Z UID:0000000021@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. Karyn Le Hur\, Yale University\n\nLow-Dimensional Qu antum Systems\n\nSystems of low dimensions have provided special opportuni ties\, challenges\, and fascination for condensed matter physicists. Issue s of long-range order\, dimensional crossover\, and instabilities are all significant in such systems. In this Talk\, I provide a pedagogical overvi ew of my theoretical research in relation to low-dimensional electron syst ems ranging from nano “zero-dimensional” systems to (quasi) twodimensi onal systems such as high-Tc superconductors\, graphene\, topological insu lators and novel oxide heterostructures. We shall also spend some time on onedimensional systems which are described by the Tomonaga-Luttinger parad igm. Finally\, I show that condensed matter concepts can also be applied t o cold atoms in optical lattices and photon systems. \n\nContact Person: n ot specified LOCATION:Seminar Room ITP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Matthias Sperl DTSTART;TZID=Europe/Berlin:20110204T163000 DTEND;TZID=Europe/Berlin:20110204T173000 DTSTAMP:20260527T090436Z UID:0000000034@events.thp.uni-koeln.de DESCRIPTION:Dr. Matthias Sperl\, Institut für Materialphysik im Weltraum\ , DLR Köln\n\nGlass-Transition Singularities\n\nAt the glass transition\, no thermodynamic anomalies or diverging length scales in static propertie s have been\nseen so far experimentally. On the other hand\, dynamical cor relation functions diverge at the transition and\nshow rich features over many orders of magnitude in time. One approach to explain glassy dynamics is the\nframework of mode-coupling theory: The equations of motion for den sity correlation functions in a fluid are\napproximated self-consistently and in the long-time limit yield glass- transition singularities. Such\nsi ngularities are known from caustics in optics (e.g. seen in rainbows and c offee mugs)\, and in fluids they\nexplain many features in glassy dynamics .\n\nIn addition to liquid-glass transitions\, the theory predicts glass-g lass transitions. These glass-glass\ntransitions are a consequence of the mathematical structure of the theory\, and their experimental confirmation \ntherefore lends credibility to the theory. The mathematical features and dynamical predictions of the theory\nshall be demonstrated with data from colloidal suspensions\, liquid water\, and static granular matter.\n\n\nC ontact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Nick Manton DTSTART;TZID=Europe/Berlin:20110408T163000 DTEND;TZID=Europe/Berlin:20110408T180000 DTSTAMP:20260527T090436Z UID:0000000053@events.thp.uni-koeln.de DESCRIPTION:Prof. Nick Manton\, DAMTP\, University of Cambridge\n\nVortice s and their geometry\n\nThe equations of the Ginzburg-Landau theory of sup erconductivity retain\ntheir mathematical fascination. The talk will discu ss various results\nconcerning the vortex solutions in two dimensions at t he critical point\nbetween the Type I and Type II regime. Here vortices ne ither attract\nnor repel\, so there are many static vortex and multi-vorte x solutions.\nThese also exist in curved background geometries. In a model where the\nvortices can move ballistically\, one can study the effective mass of one\nvortex\, what happens in vortex collisions\, and the properti es of an\ninteracting gas of many vortices. There are some precise but sur prising\nmathematical results here. Whether they have physical relevance i s (at\nleast for the speaker) an open issue.\n\n\nContact Person: not spec ified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Arne Traulsen DTSTART;TZID=Europe/Berlin:20110415T163000 DTEND;TZID=Europe/Berlin:20110415T180000 DTSTAMP:20260527T090436Z UID:0000000049@events.thp.uni-koeln.de DESCRIPTION:Dr. Arne Traulsen\, MPI for Evolutionary Biology\, Plön\n\nEv olutionary game theory: How noise can affect the evolution of cooperation and punishment\n\nTraditionally\, evolutionary game dynamics is described in terms of\ndeterministic differential equations. In the past years\, evo lutionary game\ndynamics has benefitted from considering finite population s\, which adds a\nnatural source of noise. The intensity of selection\, wh ich corresponds to an\ninverse temperature\, determines the interplay betw een selection and noise.\nWeak selection allows numerous new results in st ochastic evolutionary game\ndynamics\, but sometimes also strong selection allows analytical results.\nTheoretical aspects of this development will be discussed and examples from\nthe evolution of cooperation and punishmen t will be given\, where noise can\nbecome crucial for the dynamics.\n\n\nC ontact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Klaus Hornberger DTSTART;TZID=Europe/Berlin:20110429T163000 DTEND;TZID=Europe/Berlin:20110429T180000 DTSTAMP:20260527T090436Z UID:0000000058@events.thp.uni-koeln.de DESCRIPTION:Prof. Klaus Hornberger\, University of Duisburg-Essen\n\nEnvir onmental distinction of pointer states\n\nAn important aspect for understa nding the emergence of classical dynamics in a quantum mechanical framewor k\nis to explain the origin of super-selection rules observed at macroscop ic scales. Two specific cases will be\ndiscussed\, based on microscopicall y realistic master equations.\nIn the first part\, I will show how the dis tinction and stability of chiral molecular configuration states can be\nex plained by decoherence. In the second part\, the emergence and dynamics of motional pointer states will be\nexplored\, by associating them with the solitonic solutions of a nonlinear equation related to a particular\nstoch astic unraveling of the appropriate master equation.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Andrew Mitchell DTSTART;TZID=Europe/Berlin:20110506T163000 DTEND;TZID=Europe/Berlin:20110506T180000 DTSTAMP:20260527T090436Z UID:0000000056@events.thp.uni-koeln.de DESCRIPTION:Dr. Andrew Mitchell\, Institut für Theoretische Physik\, Univ ersität zu Köln\n\nReal-Space Renormalization Group Flow in Kondo System s\n\nThe Kondo effect is a classic paradigm in condensed matter theory\, w hich describes the dynamic screening of a quantum impurity embedded in a m etallic host. The underlying renormalization group (RG) description of suc h problems is by now very well understood. But comparatively little is kno wn in real-space: while a length-scale associated with the screening proce ss has been proposed theoretically\, its physical interpretation remains c ontroversial. We demonstrate that as one moves away from the impurity\, ph ysical quantities evolve in a characteristic way\, reproducing fully the R G flow between fixed points. Behaviour typical of each fixed point can thu s be identified in distinct regions of space. The implications of these re sults are discussed in relation to the popular 'Kondo screening cloud' pic ture. \n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Ganna Rozhnova DTSTART;TZID=Europe/Berlin:20110513T163000 DTEND;TZID=Europe/Berlin:20110513T180000 DTSTAMP:20260527T090436Z UID:0000000064@events.thp.uni-koeln.de DESCRIPTION:Dr. Ganna Rozhnova\, Universidade de Lisboa\n\nStochastic fluc tuations in systems with intrinsic noise\n\nIn this talk\, we will describ e a mechanism that generates oscillations in simple stochastic models of e pidemic dynamics. We will show that\, first\, intrinsic (demographic) stoc hasticity can generate large coherent fluctuations which behave as sustain ed oscillations and that\, second\, the power spectrum of these fluctuatio ns can be calculated analytically using the system size expansion. The app lication of this analysis to the problem of the modeling of recurrent epid emics shows that\, in systems whose sizes represent real populations\, the role of stochastic effects becomes fundamental for the interpretation of historical data.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. D. Vollhardt DTSTART;TZID=Europe/Berlin:20110520T163000 DTEND;TZID=Europe/Berlin:20110520T180000 DTSTAMP:20260527T090436Z UID:0000000017@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. D. Vollhardt\, University of Augsburg\n\nConstructio n of exact ground states for correlated electron models\n\nA general schem e for the construction of exact ground states of correlated electron model s will\nbe discussed. It consists of three steps: The transformation of th e Hamiltonian into positive semidefinite\nform\, the construction of many- particle ground states of this Hamiltonian\, and the proof of the\nuniquen ess of these ground states. This approach works in any dimension\, assumes no integrability of\nthe model and only requires sufficiently many micros copic parameters in the Hamiltonian. Thereby\nground states of diamond Hub bard chains are constructed which exhibit a multitude of properties such\n as flat-band ferromagnetism and correlation induced metallic\, half-metall ic or insulating behavior.\nFurthermore\, the exact ground state of a 1D p eriodic Anderson model is shown to explain the unusual\nferromagnetism in the f electron material CeRh3B2. Finally\, it is proved that pentagon chai n polymers\nmay be designed to become ferromagnetic or half metallic.\n\nC ontact Person: not specified LOCATION:Seminar Room ITP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Armin Bunde DTSTART;TZID=Europe/Berlin:20110527T163000 DTEND;TZID=Europe/Berlin:20110527T180000 DTSTAMP:20260527T090436Z UID:0000000069@events.thp.uni-koeln.de DESCRIPTION:Prof. Armin Bunde\, Justus-Liebig Universität Giessen\n\nLong -term correlations in nature: On the clustering of extreme events and the estimation of external trends\n\nIn this talk\, I discuss  long-term memo ry  in nature (particularly in climate) and its implications for the occu rrence of extremes.\nI also show how external trends can be estimated in r ecords with long-term memory and apply the results\nto the estimation of  anthropogenic global warming.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Royce K.P. Zia DTSTART;TZID=Europe/Berlin:20110610T163000 DTEND;TZID=Europe/Berlin:20110610T180000 DTSTAMP:20260527T090436Z UID:0000000062@events.thp.uni-koeln.de DESCRIPTION:Prof. Royce K.P. Zia\, Virginia Tech\, Blacksburg\n\nTowards a classification scheme for non-equilibrium steady states\n\nWe propose a g eneral classification of nonequilibrium steady states in terms of their st ationary probability distribution and the associated probability currents. The stationary\nprobabilities can be represented graph-theoretically as d irected Cayley trees\; closing a single loop in such a graph leads to a re presentation of probability currents. This classification\nallows us to id entify all choices of transition rates\, based on a master equation\, whic h generate the same nonequilibrium steady state. We explore the implicatio ns of this freedom\, e.g.\,\nfor entropy production\, and provide a number of examples.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr Tim Newman DTSTART;TZID=Europe/Berlin:20110624T163000 DTEND;TZID=Europe/Berlin:20110624T173000 DTSTAMP:20260527T090436Z UID:0000000054@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr Tim Newman\, University of Dundee\n\nEmbryogenesis an d cancer progression: discrete theoretical methods applied to living syste ms\n\nThe discreteness of biological components\, whether they be proteins in a cell or individuals in an ecological population\, has important\ncon sequences for the dynamics of biological systems. This concept is quite na tural for statistical physicists\, but not widely recognised\nin the life sciences. I will discuss some examples relevant to cell biology\, cancer p rogression\, and embryo development\, in which\nstochastic process theory along with agent-based computer simulations have helped provide new insigh ts and understanding.\n\n\nContact Person: not specified LOCATION:Seminar Room ITP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. A. Altland DTSTART;TZID=Europe/Berlin:20110715T163000 DTEND;TZID=Europe/Berlin:20110715T173000 DTSTAMP:20260527T090436Z UID:0000000091@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. A. Altland\, Institut für Theoretische Physik\, Uni versität zu Köln\n\nQuantum phase transitions in the cold atom kicked ro tor\n\nI will discuss the physics of transport phenomena in\ndriven chaoti c environments (`kicked rotors')\, as\nrealized in recent atom optic exper iments. The behavior\nof these systems depends sensitively on the value of a \nscaled Planck constant \\tilde h: for irrational values of\n\\tilde h /(4\\pi) they fall into the universality class of\ndisordered electronic s ystems and I will discuss the corresponding\nlocalization phenomena. In co ntrast\, for rational values the\nrotor-Anderson insulator acquires an inf inite conductivity\nand turns into a `super-metal'. This implies the exis tence of a novel \n'metal/super-metal' quantum phase transition in cold at om systems.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Erik Aurell DTSTART;TZID=Europe/Berlin:20111014T143000 DTEND;TZID=Europe/Berlin:20111014T153000 DTSTAMP:20260527T090436Z UID:0000000118@events.thp.uni-koeln.de DESCRIPTION:Erik Aurell\, KTH Royal Institute of Technology\, Sweden\, and Aalto University\, Finland\n\nComputing stationary states by message-pass ing\n\nComputing marginals of probability distributions (magnetizations\, spin-spin correlations\netc) is an important problem in statistical physic s of disordered systems and many \nother fields. In decision problems one typically wants to estimate the likelihood\nthat a single variable takes a given value\, given the interactions with all the\nother variables\, then fix that variable to its most likely value\, and so estimate the\nmost li kely configuration of all the variables. An important technical applicatio n\nis decoding in communication systems\, where the task is to estimate th e code word\nmost likely to have been sent from the recieved signal and wh at one knows about the\nchannel.\n\nIn principle one can compute the margi nals of any Markov chain by Monte Carlo\, but\nsuch methods are inherently slow for large systems. Over the last decade there has \ntherefore been i ntense interest in approximate methods to compute marginals of probability \ndistributions deterministically (the cavity method\, Belief Propagation \, iterative decoding)\,\nwhich overall work by nodes (representing variab les) sending messages between each other\nand so collectively yield someti mes exact and often very good estimates of the marginals. In \nthe languag e of physics all these methods compute a variational ansatz of the Boltzma nn-Gibbs \nfree energy of an equilibrium statistical mechanical system whe re the messages are related to \nLagrange multipliers.\n\nI will describe recent work on extending message-passing from computing the stationary\nst ates of Markov chains obeying detailed balance to Markov chains which do n ot. This\n"dynamic cavity method" works to some extent\, and in particular outperforms dynamic\nmean-field methods on standard kinetic (non-equilibr ium) Ising systems. \n\nThis is joint work with Hamed Mahmoudi (2011a-c)\, building on earlier work by Montanari\nand co-workers (2009) and Neri and Bolle (2009).\n \n\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Jonas Larson DTSTART;TZID=Europe/Berlin:20111021T163000 DTEND;TZID=Europe/Berlin:20111021T180000 DTSTAMP:20260527T090436Z UID:0000000114@events.thp.uni-koeln.de DESCRIPTION:Dr. Jonas Larson\, University of Cologne and Stockholm Univers ity\n\nSynthetic magnetic fields for neutral ultracold atoms\n\nI will bri efly review some recent developments on how to achieve and manipulate  effective gauge fields for ultracold atoms. Starting with some historical remarks on effective\ngauge theories in molecular and time-dependent syst ems\, I move on to show how this translates to ultracold atoms exposed to spatially varying laser fields. This research has gained great\nattention lately\, and the experimental efforts are seriously beginning to pay off . At the present\, the non-Abelian case has not been experimentally demons trated but will in the near\nfuture... An important example of a non-Abeli an gauge potential is the one of Rashba\, which for a particular choice of atom-laser configuration can be constructed in these systems. This\nop ens the door for sudies of effects such as\, spin Hall currents\, relativi stic Zitterbewegung\, half quantized vortices. Combined with optical latti ces\, there's even hope to explore\nquantized Hall physics and interesti ng physics that comes with it.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Günter Radons DTSTART;TZID=Europe/Berlin:20111104T163000 DTEND;TZID=Europe/Berlin:20111104T180000 DTSTAMP:20260527T090436Z UID:0000000098@events.thp.uni-koeln.de DESCRIPTION:Prof. Günter Radons\, TU Chemnitz\n\nNonlinear Dynamics of Co mplex Hysteretic Systems\n\nUnder the influence of external fields a large variety of materials and systems shows complex hysteretic behavior. The latter means that in addition to major hysteresis loops\, one finds\nmany subloops or minor loops\, if the external field is reversed or oscillates at some intermediate values. Well-known examples range from adsorption in porous media to the magnetization\nof magnetic materials. Such a behavior is traditionally described by so-called hysteresis operators\, for which t he Preisach operator is one of the most prominent representatives.\nCorres pondingly\, the interaction of such hysteretic systems with its environmen t is naturally described by operator-differential equations. Despite its i mportance the dynamics resulting\nfrom such equations is not well understo od. In this talk I will review the working principles of the Preisach hyst eresis operator and its applications. Subsequently recent results on dynam ical systems with such hysteretic\nsubsystems will be presented. They rang e from the appearance of 1/f-noise under simple input-output conditions to the co-existence of infinitely many attractors for\noperator-difference o r operator-differential equations describing e.g. the motion of an iron sa mple in an inhomogeneous magnetic field.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Armin Bunde DTSTART;TZID=Europe/Berlin:20111118T163000 DTEND;TZID=Europe/Berlin:20111118T180000 DTSTAMP:20260527T090436Z UID:0000000099@events.thp.uni-koeln.de DESCRIPTION:Prof. Armin Bunde\, Justus-Liebig Universität Giessen\n\nLong -term correlations in nature: On the clustering of extreme events and the estimation of external trends\n\nIn this talk\, I discuss long-term memor y in nature (particularly in climate) and its implications for the occurr ence of extremes.\nI also show how external trends can be estimated in rec ords with long-term memory and apply the results to the estimation of ant hropogenic global warming.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Gregory Schehr DTSTART;TZID=Europe/Berlin:20111202T163000 DTEND;TZID=Europe/Berlin:20111202T180000 DTSTAMP:20260527T090436Z UID:0000000121@events.thp.uni-koeln.de DESCRIPTION:Dr. Gregory Schehr\, University Paris-Sud\n\nExtreme value sta tistics of non-intersecting Brownian motions : from random matrices to 2d Yang-Mills theory on the sphere\n\nNon-intersecting random walkers (or ''v icious walkers'') have been studied\nin various physical situations\, rang ing from polymer physics to wetting\nand melting transitions and more rece ntly in connection with random matrix\ntheory or stochastic growth process es. In this talk\, I will present a\nmethod based on path integrals associ ated to free Fermions models to study\nsuch statistical systems. I will us e this method to calculate exactly the\ncumulative distribution function ( CDF) of the maximal height of p vicious\nwalkers with a wall (excursions) and without a wall (bridges). In the case\nof excursions\, I will show tha t the CDF is identical to the partition\nfunction of 2d Yang Mills theory on a sphere with the gauge group Sp(2p).\nTaking advantage of a large p an alysis achieved in that context\, I will\nshow that the CDF\, properly shi fted and scaled\, converges to the\nTracy-Widom distribution for $\\beta = 1$\, which describes the fluctuations\nof the largest eigenvalue of Rando m Matrices in the Gaussian Orthogonal\nEnsemble.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Dmitri Diakonov DTSTART;TZID=Europe/Berlin:20111209T163000 DTEND;TZID=Europe/Berlin:20111209T180000 DTSTAMP:20260527T090436Z UID:0000000119@events.thp.uni-koeln.de DESCRIPTION:Dr. Dmitri Diakonov\, Petersburg Nuclear Physics Institute\n\n Towards microscopic quantum gravity\n\nThe Einstein – Hilbert action of General Relativity is not fit to describe quantum fluctuations of the metr ics as it does not restrict either large fluctuations or fast varying ones . Therefore\, it defines at best an effective theory which\, of course\, i s tremendously successful. A hint how to construct a true and well defined `microscopic’ gravitation theory is provided by the fact that there are fermions in Nature. Fermions require that the field variables to be used are the vierbein and the Lorentz spin connection. This leads to Cartan’s formulation of General Relativity\, but field fluctuations are not restri cted there either because none of the possible general covariant action te rms is sign-definite. A way out is to present the vierbein as a bilinear "current" of more fundamental fermion (spinor) fields. Path integrals over Grassmann variables are well defined for whatever sign of the fermion act ion. We suggest that in the ultraviolet limit quantum gravity possesses on ly spinor and gauge field degrees of freedom\, like in the Standard Model. The theory can be easily regularized by putting it on a space lattice. It is explicitly invariant under local Lorentz transformations and\, in the continuum limit\, under diffeomorphisms. It is a theory that is well-behav ed at small distances\, and quantum fluctuations are well defined. We disc uss how to check if Newton’s law is reproduced in the infrared limit in the world with fluctuating metrics. Our formulation of quantum gravity all ows its unification with the Standard Model\, and that will be also briefl y discussed. \n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. Milena Grifoni DTSTART;TZID=Europe/Berlin:20111216T163000 DTEND;TZID=Europe/Berlin:20111216T173000 DTSTAMP:20260527T090436Z UID:0000000131@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. Milena Grifoni\, University of Regensburg\n\nQuantum interference effects in interacting quantum dots \n\nWe consider multiple quantum dots or molecular junctions in the single-electron tunneling regi me which\, due to a high degree of spatial\nsymmetry\, have a degenerate m any-body spectrum. As a consequence\, interference phenomena which cause a \ncurrent blocking can occur at specific values of the bias and gate volta ge. We present here\n necessary and sufficient conditions for interference blockade also in the presence of spin-polarized\nleads. As an example we analyze a benzene single-electron transistor. For a setup with parallel\np olarized leads\, we show how to exploit the current blocking to selectivel y prepare the system in a defined spin state\n without application of any external magnetic field.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. J. Schmalian DTSTART;TZID=Europe/Berlin:20120113T163000 DTEND;TZID=Europe/Berlin:20120113T173000 DTSTAMP:20260527T090436Z UID:0000000140@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. J. Schmalian\, KIT Karlsruhe\n\nDiscrete scale invar iance and non-Ginzburg-Landau criticality near quantum percolation transit ions\n\nWe analyze the low-energy excitations of diluted Josephson-junctio ns arrays\, XY-quantum antiferromagnets\, and interacting bosons near the percolation threshold. We then show that the\ncritical behavior of these systems is dramatically altered by the presence of a Berry phase that lead s to an order parameter precession and\, depending on the system\, is caus ed by an\nexternal magnetic field or an external gate voltage. Most intere stingly\, the low energy excitations become spinless fermions with a fract al spectrum. As a result\, critical properties not\ncaptured by the usual Ginzburg-Landau-Wilson description of phase transitions emerge\, such as c omplex critical exponents\, log-periodic oscillations and dynamically brok en scale-invariance.\n[Rafael M. Fernandes\, Jörg Schmalian\, Phys.Rev.Le tt.106\, 067004 (2011)]\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Simon Trebst DTSTART;TZID=Europe/Berlin:20120120T163000 DTEND;TZID=Europe/Berlin:20120120T180000 DTSTAMP:20260527T090436Z UID:0000000138@events.thp.uni-koeln.de DESCRIPTION:Prof. Simon Trebst\, University of Cologne\n\nInteractions and disorder in topological quantum matter\n\nThe emergence of topological or der is one of the most intriguing phenomena in quantum many-body physics a nd one of possibly far reaching relevance - topological quantum matter is\ nincreasingly appreciated as possible medium for quantum computation purpo ses. In this talk\, I will discuss the stability of topological quantum ma tter when considering the effects of\ninteractions and disorder on the col lective quantum state formed by a set of topological excitations\, so-call ed anyons. In particular\, I will discuss the formation of a thermal metal of\nMajorana fermions in a two-dimensional system of interacting non-Abel ian anyons in the presence of moderate disorder. This bulk metallic phase occurs for various proposed systems\nsupporting Majorana fermion zero mode s when disorder induces the random pinning of a finite density of vortices . This includes all two-dimensional topological superconductors in\nso-cal led symmetry class D. A distinct experimental signature of the thermal met al phase is the presence of bulk heat transport down to zero temperature. I will finish by discussing\nimplications for topological quantum computin g proposals. \n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. Hildegard Meyer-Ortmanns DTSTART;TZID=Europe/Berlin:20120127T163000 DTEND;TZID=Europe/Berlin:20120127T180000 DTSTAMP:20260527T090436Z UID:0000000122@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. Hildegard Meyer-Ortmanns\, Jacobs University Bremen\ n\nOn the versatile role of fluctuations in biological systems\n\nNoise is ubiquitous in dynamical systems. Its impact on the dynamics can be quite versatile\, ranging from bad signal-to-noise ratios to qualitatively new p henomena such as oscillations\nof populations\, which would be absent with out noise. Here "noise" stands for stochastic fluctuations of various orig in. Of particular interest are stochastic fluctuations in the context\nof biology. What is their role in evolutionary processes or in the living cel l as the basic unit of life? We shall focus on a dynamical unit which cons ists of only two species\ninteracting in a non-linear way. This unit may b e regarded as a coarse-grained description of a genetic circuit. For compa rison we shall first discuss the unit in a deterministic\ndescription and then turn to a fully stochastic one. There we shall unravel the effect of demographic fluctuations and fluctuations in the reaction times. The power spectrum will show\nwhich source of stochastic behavior is dominant. We s hall compare analytic predictions with Gillespie simulations. The results raise an interesting generic question about oscillatory\ngenetic systems observed in nature.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Alexander Ludwig DTSTART;TZID=Europe/Berlin:20120203T163000 DTEND;TZID=Europe/Berlin:20120203T180000 DTSTAMP:20260527T090436Z UID:0000000141@events.thp.uni-koeln.de DESCRIPTION:Prof. Alexander Ludwig\, Cen­ter for Ma­cro­eco­no­mic Re ­se­arch\, Cologne \n\nOn the Welfare Effects of Social Security in a Mo del with Aggregate and Idiosyncratic Risk\n\nWe study the welfare eff ects of social security in an overlapping\ngenerations general equilibrium mod el with aggregate and idiosyncratic\nrisk. Prior research on social securi ty has only considered either\naggregate or idiosyncratic risk. We show an alytically that the\naggregate and idiosyncratic risks interact due to the life-cycle structure\nof the economy. This interaction increases the welf are gains of a\nmarginal introduction of an unfunded social security syste m. Adding\na second interaction by making the variance of the idiosyncrati c risk\ncountercyclical further increases the welfare gains. In our quanti tative\nexperiment\, raising the contribution rate from zero to two percen t\nleads to long-run welfare gains of 3.5% of life-time consumption on ave rage\,\neven though the economy experiences substantial crowding out\nof c apital. Approximately one third of these gains can be attributed\nto the i nteractions between idiosyncratic and aggregate risk.\n\nContact Person: n ot specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Boris Gutkin DTSTART;TZID=Europe/Berlin:20120413T163000 DTEND;TZID=Europe/Berlin:20120413T180000 DTSTAMP:20260527T090436Z UID:0000000160@events.thp.uni-koeln.de DESCRIPTION:Dr. Boris Gutkin\, University of Duisburg-Essen\n\nClustering of periodic orbits in chaotic systems\n\nStatistics of energy levels in Ha miltonian systems with classically\nchaotic dynamics belong to one of thre e Wigner-Dyson symmetry classes. By\nthe semiclassical approach this remar kable universality can be attributed\nto the systematic correlations betwe en actions of periodic orbits. The\ncorrelating periodic orbits do not exi st as independent individuals\nbut rather come in closely packed bunches. We demonstrate how this\nbunching phenomena can be rigorously described us ing symbolic\ndynamics of the system.\n\nFor systems with Markov partition we introduce an ultrametric\ndistance between periodic orbits and organiz e them into clusters.\nEach cluster is composed of periodic orbits passin g through\n(approximately) the same points of the phase space. We then stu dy the\ndistribution of cluster sizes in the asymptotic limit of long\ntra jectories. In the case of the baker's map this problem turns out to be\neq uivalent to the one of counting degeneracies in the length spectrum\nof de Bruijn graphs.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Alexander Altland DTSTART;TZID=Europe/Berlin:20120420T163000 DTEND;TZID=Europe/Berlin:20120420T180000 DTSTAMP:20260527T090436Z UID:0000000158@events.thp.uni-koeln.de DESCRIPTION:Prof. Alexander Altland\, University of Cologne\n\nQuantum the rmalization\n\nIn this talk\, I will discuss mechanisms by which (nonlinea r) quantum systems effectively 'thermalize' into long time stationary dist ributions. \nFocusing on the paradigmatic example of the Dicke model (a la rge spin coupled to a boson mode)\, I will demonstrate how a constructive description of the thermalization process is\nfacilitated by the Glauber Q or Husimi function\, for which the evolution equation turns out to be of Fokker-Planck type. The equation describes a competition of classical inst abilities\nand quantum diffusion. By this mechanism the system follows a " quantum smoothened" approach to equilibrium\, which avoids the notorious s ingularities inherent to classical chaotic flows.\nI will touch upon the r elevance of the above picture to recent experiments in cold atom physics.\ n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Wojciech De Roeck DTSTART;TZID=Europe/Berlin:20120427T163000 DTEND;TZID=Europe/Berlin:20120427T180000 DTSTAMP:20260527T090436Z UID:0000000164@events.thp.uni-koeln.de DESCRIPTION:Dr. Wojciech De Roeck\, University of Cologne\n\nA rigorous ap proach to quantum Brownian motion\n\nThis talk concerns the rigorous deriv ation of diffusion\, thermalization and decoherence in simple quantum syst ems: a spin or a particle interacting with phonons.\nOur approach takes th e Markovian description (Pauli master equation or quantum Boltzmann equati on) as a starting point. However\, since such a Markovian description is o nly valid in a\ncertain scaling limit (vanishing coupling constant and lon g time)\, we develop an expansion around the Markovian description to cont rol the behavior at finite coupling constant. This\nexpansion consists of a controlled renormalization group flow with Brownian motion as the fix-p oint solution.\n\nThe long-range nature of the velocity-velocity correlati on function is an example of a physical quantity that is not described cor rectly within the Markovian description (cfr. Alder-Wainwright)\, but that is captured by our approach.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Mark Oliver Goerbig DTSTART;TZID=Europe/Berlin:20120504T163000 DTEND;TZID=Europe/Berlin:20120504T173000 DTSTAMP:20260527T090436Z UID:0000000163@events.thp.uni-koeln.de DESCRIPTION:Dr. Mark Oliver Goerbig\, Universite Paris Sud\n\nGraphene Fra ctional Quantum Hall Effect and Internal Symmetries\n\nA milestone in grap hene research was the 2005 discovery of an \ninteger quantum Hall effect. In contrast to its manifestation \nin conventional two-dimensional (2D) el ectron systems\, such \nas in semiconductor heterostructures\, the graphen e quantum \nHall effect reflects the "ultra-relativistic" character of \nt he underlying carriers\, via a particular sequence of plateaus \nin the tr ansverse Hall resistance.\n\nIn view of the fractional cousin of the integ er quantum Hall \neffect in 2D electron systems\, one may thus naturally a sk the \nquestion about a fractional quantum Hall effect in graphene. \nDo es it also reflect the ultra-relativistic character of the \ncharge carrie rs? To what extent is it different from the \nfractional quantum Hall effe ct in (non-relativistic) \nsemiconductor heterostructures? Many of these q uestions remain \nopen from an experimental point of view\, although some \nfractional states have recently been observed in transport \nand spectro scopic measurements.\n\nThis talk aims at a theoretical perspective on the fractional \nquantum Hall effect in graphene\, namely in view of its \nmu lti-component character due to the fourfold spin-valley \ndegeneracy\, whi ch gives rise to an internal SU(4) symmetry \nand that is approximately re spected by the underlying \nelectron-electron interactions. This theoretic al perspective \nwill be confronted with recent experimental advances.\n\n \nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Kirill Shtengel DTSTART;TZID=Europe/Berlin:20120511T163000 DTEND;TZID=Europe/Berlin:20120511T173000 DTSTAMP:20260527T090436Z UID:0000000168@events.thp.uni-koeln.de DESCRIPTION:Prof. Kirill Shtengel\, UC Riverside\n\nNon-Abelian anyons: Ne w particles for less than a billion\n\nStates of matter are conventionally classified according to broken\nsymmetries. Topologically ordered phases fall outside of this paradigm:\nwith no local order parameter\, they never theless have many peculiar\nproperties setting them apart from disordered phases. In 2D\, such\nphases may support anyons - quasiparticles that are neither bosons\nnor fermions. Moreover\, anyons with non-Abelian statistic s are\nexpected to occur in certain fractional quantum Hall systems as wel l\nas materials supporting topological superconductivity (intrinsic or\nin duced).\nIn this talk\, I will discuss various approaches designed to\ndet ect such exotic statistics. I will also describe our recent\nproposal for novel physical systems supporting unusual non-Abelian\nanyons. I will also mention potential applications of such systems for\ntopological quantum c omputation.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Sabine Lennartz DTSTART;TZID=Europe/Berlin:20120518T163000 DTEND;TZID=Europe/Berlin:20120518T180000 DTSTAMP:20260527T090436Z UID:0000000157@events.thp.uni-koeln.de DESCRIPTION:Dr. Sabine Lennartz\, University of Edinburgh\n\nInverse power -law like crack growth in earth materials and its possible origin as an em ergent property of localisation\n\nThe origin and development of cracks in earth materials is a subject of\ngeneral interest and wide application: f rom seismologists studying\nearthquakes to engineers studying the strength of materials. Therefore\nmany laboratory experiments have been carried ou t to investigate the\nresponse of rocks to an applied differential stress\ , often using\nacoustic emissions (AE) to track intermittent crack growth inside the\nrock specimen prior to system-sized sample failure. Under a co nstant\napplied stress in double-torsion tensile tests with a guide groove and a\nsingle dominant crack\, independent observations of the stress int ensity\nfactor and crack growth velocity imply the size of the largest (su b-)\ncritical crack grows with time t according to an inverse power-law. \ nA similar law holds for the mean crack length in a\npopulation of micro-c racks growing under compressional stress with no\npre-defined fault plane\ , often treated using mean field models that\nignore localisation of damag e clearly seen in the experiments. Here I\npresent a new hypothesis for th e origin of this formula by combining\nexpressions for crack population gr owth and localisation in a single\nmodel. The model is tested and some of its parameters inferred from\nanalysis of the AE rate and the spatial clus tering of its source\nlocations from laboratory data.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. I. Müller DTSTART;TZID=Europe/Berlin:20120525T163000 DTEND;TZID=Europe/Berlin:20120525T173000 DTSTAMP:20260527T090436Z UID:0000000159@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. I. Müller\, TU Berlin\n\nThe terroristic nimbus of entropy - on the history of thermodynamics\n\nThe development of thermodyn amics in the second half of the \n19th century has had a strong impact on both technology and \nnatural philosophy.\nIt is true that the steam engin e for the conversion of heat \ninto work existed before thermodynamics was developed as a \nbranch of physics. However\, the systematic theory impro ved \nthe conversion process\, and it succeeded in developing other \nproc esses essential to modern life\, notably refrigeration and \nrectification . So\, altogether thermodynamics has provided \nhumanity with cheap energy \, and cheap fuel\, - consequently \nwith cheap\, and abundant\, and unspo iled food. Thus \nthermodynamics has made populations grow\, and life expe ctancy \nincrease beyond anything people could possibly have imagined \n20 0 years ago. \nAt the same time thermodynamics has uncovered the precariou s \nbalance between determinism and stochasticity which is essential \nto processes on earth\, including life. The competition of those \nintentions is described by the doctrine of energy and entropy \nin thermodynamics\; energy tends to force a system into one \nsingle state\, and entropy tends to spread the system evenly \nover all possible states. These competing t endencies are weighed by\ntemperature such that minimal energy determines cold systems and\nmaximal entropy determines hot systems.\n\n\nContact Per son: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Subir Sachdev DTSTART;TZID=Europe/Berlin:20120608T163000 DTEND;TZID=Europe/Berlin:20120608T173000 DTSTAMP:20260527T090436Z UID:0000000170@events.thp.uni-koeln.de DESCRIPTION:Prof. Subir Sachdev\, Harvard\n\nStrange metals: field theory versus gauge-gravity duality\n\nThe description of non-Fermi liquid metals is one of the central problems in the theory of correlated electron syste ms. I present a holographic theory which builds on general features of the thermal entropy density and the entanglement entropy. Remarkable connecti ons emerge between the holographic approach\, and the postulated strong-co upling behavior of the field theory.\n\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. Heiko Rieger DTSTART;TZID=Europe/Berlin:20120615T163000 DTEND;TZID=Europe/Berlin:20120615T180000 DTSTAMP:20260527T090436Z UID:0000000178@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. Heiko Rieger\, Universität des Saarlandes\n\nBiophy sical models for tumor growth\n\nTumor growth is a multifactorial process that surely emerges from molecular and genetic abnormalities\, but also de pends strongly on cell-cell and cell-extracellular matrix macroscopic\nreg ulations and interactions. Numerous models have been developed to understa nd the mechanisms controlling solid tumor morphogenesis: While the earlies t efforts were focusing on cell\nproliferation kinetics\, modulated by the availability of supplied nutrients\, new approaches emphasize the crucial role of several biophysical processes\, including local matrix\nremodelin g\, active cell migration and traction\, and reshaping of the host tissue blood vessel network. In this talk a brief review over a number of represe ntative models will be given\,\nin particular those predicting the emergen ce of invasive behavior through growth instabilities at the tumor-host int erface. Then the focus will be put on the analysis of vascular\nremodeling during tumor growth within a theoretical model including angiogenesis\, c ooption and regression of blood vessels. The physical mechanisms determini ng the morphological and\nhydrodynamical characteristics of the emerging t umor vasculature are analyzed and implications for blood borne drug delive ry are discussed.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Pascal Simon DTSTART;TZID=Europe/Berlin:20120706T163000 DTEND;TZID=Europe/Berlin:20120706T173000 DTSTAMP:20260527T090436Z UID:0000000183@events.thp.uni-koeln.de DESCRIPTION:Pascal Simon\, Université Paris Sud\n\nMajorana polarization and transport properties in 1D topological superconductors\n\nI will prese nt recent results on a one-dimensional wire with strong Rashba\nand Dresse lhaus spin-orbit coupling (SOC)\, which supports Majorana\nfermions when s ubject to a Zeeman magnetic field and in proximity of a\nsuperconductor. B y introducing a new local quantity dubbed as "Majorana\npolarization"\, I will argue that it can be used as a local order\nparameter to characteriz e the topological transition between a trivial\nsystem and a system exhibi ting Majorana bound modes. We have found that\nthe local "Majorana polariz ation" is correlated to the transverse spin\npolarization\, and we propose to test the presence of Majorana fermions in\na 1D system by a spin-polar ized density of states measurement. Such\nquantity turns out to be very us eful to analyze one-dimensional\ntopological SN and SNS long junctions obt ained by placing a topological\ninsulating nanowire in the proximity of ei ther one or two superconducting\nfinite-size leads: for a finite-size SN j unction the Andeev Bound States\n(ABS) spectrum exhibits a zero-energy ext ended state which carries a full\nMajorana fermion\, while the ABS of long SNS junctions with phase\ndifference pi transform into two zero-energy st ates carrying two\nMajorana fermions.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Martin Evans DTSTART;TZID=Europe/Berlin:20120713T163000 DTEND;TZID=Europe/Berlin:20120713T180000 DTSTAMP:20260527T090436Z UID:0000000181@events.thp.uni-koeln.de DESCRIPTION:Prof. Martin Evans\, University of Edinburgh\n\nDiffusion with stochastic resetting\n\n"Stochastic resetting" is a rather common process in everyday\nlife. Consider searching for some target such as\, for examp le\, a face in a\ncrowd or one's misplaced keys at home. A natural tendenc y is\, on having\nsearched unsuccessfully for a while\, to return to the s tarting point and\nrecommence the search. In this talk I explore the conse quences of such\nresetting on perhaps the most simple and common process i n nature\, namely\,\nthe diffusion of a single or a multiparticle system. It turns out that a\nnonzero rate of resetting has a rather rich and drama tic effect on the\ndiffusion process\, strongly affecting the behaviour of mean first passage\ntimes and survival probabilities.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Lars Fritz DTSTART;TZID=Europe/Berlin:20121012T163000 DTEND;TZID=Europe/Berlin:20121012T173000 DTSTAMP:20260527T090436Z UID:0000000197@events.thp.uni-koeln.de DESCRIPTION:Dr. Lars Fritz\, University of Cologne\n\nTopological insulato rs: magnetic fields\, disorder\, and interactions\n\nIn an introductory pa rt I will discuss the relation between topological insulators and the arch itectural challenge of building a bridge between Hongkong and mainland Chi na. \nThen I discuss how a magnetic field induces one-dimensional edge cha nnels when the two-dimensional surface states of three-dimensional topolog ical insulators become gapped. Remarkably\, the Hall effect remains quanti zed even in situations\, where the theta-term characteristic of the bulk a nd the associated surface Hall conductivities are not quantized due to the breaking of time-reversal symmetry. The quantization arises as the theta- term changes by integer multiples along a loop around n edge channels. Mod el calculations show how an interplay of orbital and Zeeman effects leads to quantum Hall transitions\, where channels get redistributed along the e dges of the crystal. The network of edges opens new possibilities to inves tigate the coupling of edge channels.\nIn a last part I will shortly discu ss aspects of strongly disordered topological insulators as well as intera ction effects on the surfaces.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Dirk Witthaut DTSTART;TZID=Europe/Berlin:20121102T163000 DTEND;TZID=Europe/Berlin:20121102T180000 DTSTAMP:20260527T090436Z UID:0000000194@events.thp.uni-koeln.de DESCRIPTION:Dr. Dirk Witthaut\, Max Planck Institute for Dynamics and Self -Organization\n\nSynchronization and Braess' paradox in an oscillator mode l for power grid operation\n\nPower grids\, which form the cornerstone our technical infrastructure\, will undergo a revolutionary change in the upc oming decades driven by the advancement of renewable energy sources. Large centralized power plants are put out of operation in favor of many small\ , distributed and potentially fluctuating generators. To face this enormou s challenge for the reliable operation of the power grid\, both the struct ure and control of the grid must undergo a radical change. This developmen t must be supported by a great advancement of our theoretic understanding of complex networked systems.\n\nIn this talk I discuss the collective dyn amics of power grids using an idealized oscillator model that model grid d ynamics on coarse scales. This model bridges the gap between abstract larg e-scale\, basically structural network models from physics on the one hand and detailed simulations of small electric engineering systems on the oth er. I analyze self-organized synchronization of the grid depending on the network topology and study the impact of dynamical perturbations and the i nfluence of topological changes. I find that\, contrary to common intui tion\, the addition of new transmission lines may reduce the overall grid capacity and explain this phenomenon by geometric frustration in the oscil lator model. \n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Professor Steven H. Simon DTSTART;TZID=Europe/Berlin:20121109T163000 DTEND;TZID=Europe/Berlin:20121109T173000 DTSTAMP:20260527T090436Z UID:0000000205@events.thp.uni-koeln.de DESCRIPTION:Professor Steven H. Simon\, Rudolf Peierls Centre for Theoreti cal Physics\, Oxford\n\nTopological Matter and Why You Should Be Intereste d\n\nIn two dimensional topological phases of matter\, processes depend \n on gross topology rather than detailed geometry. Thinking in 2+1 \ndimensi ons\, particle world lines can be interpreted as knots or \nlinks\, and th e amplitude for certain processes becomes a topological \ninvariant of tha t link. While sounding rather exotic\, we believe \nthat such phases of ma tter not only exist\, but have actually been \nobserved in quantum Hall ex periments\, and could provide a uniquely \npractical route to building a q uantum computer. Possibilities \nhave also been proposed for creating simi lar physics in systems \nranging from superfluid helium to strontium ruthe nate to \nsemiconductor-superconductor junctions to quantum wires to spin \nsystems to cold atoms.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. K. Wolff DTSTART;TZID=Europe/Berlin:20121116T163000 DTEND;TZID=Europe/Berlin:20121116T173000 DTSTAMP:20260527T090436Z UID:0000000206@events.thp.uni-koeln.de DESCRIPTION:Dr. K. Wolff\, TU Berlin \n\nActive particles and fluid flow\n \nActive motion of particles in aqueous solution may lead to interesting \ ncollective phenomena such as pattern formation or macroscopic fluid flows . I \nwill discuss two examples where this can be observed. First\, I will present \nlattice Boltzmann simulations of a microscopic model for cytopl asmic\nstreaming in algal cells. Here\, myosin motors entrain the surround ing fluid by \nwalking along actin filaments while dragging vesicles or ot her organelles. I \nwill pay particular attention to how the high speeds o bserved in experiments can \nbe achieved by assuming a layer of lower visc osity at the outer wall of the \nsimulated compartment. The second example is a system of sedimenting \nself-propelled particles with the additional property of bottom-heaviness\, which \nresults in a tendency of particles to swim upwards. I will give analytical \nresults for the dilute limit an d numerical results for the interacting case \nwhere particles form vortic es and columns.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Paolo Politi DTSTART;TZID=Europe/Berlin:20121123T163000 DTEND;TZID=Europe/Berlin:20121123T180000 DTSTAMP:20260527T090436Z UID:0000000190@events.thp.uni-koeln.de DESCRIPTION:Dr. Paolo Politi\, Istituto dei Sistemi Complessi\, Firenze\n\ nCoarsening: some answers to when and how it occurs\n\nMany out-of-equilib rium systems undergo an instability when an order parameter is suitably tu ned\, giving rise to well known and widespread processes: growth\, convect ion\, phase separation\, and so on. A common feature is the emergence of a nontrivial spatial structure\, whose typical scale L may display differen t dynamics. We are specially interested in understanding when L increases in time (coarsening process) and how. \nUsing a continuum modelling and a multiscale approach\, for several equations we are able to obtain a phase diffusion equation describing the dynamics of the emerging pattern and to predict when and how coarsening proceeds.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Mikhail A. Skvortsov DTSTART;TZID=Europe/Berlin:20121130T163000 DTEND;TZID=Europe/Berlin:20121130T173000 DTSTAMP:20260527T090436Z UID:0000000220@events.thp.uni-koeln.de DESCRIPTION:Dr. Mikhail A. Skvortsov\, Landau Institute of Theoretical Phy sics\, Chernogolovka \n\nSuperconducting proximity effect in quantum wires without time-reversal symmetry\n\nWe study the superconducting proximity effect in a quantum wire with\nbroken time-reversal (TR) symmetry connecte d to a superconductor. We\nconsider the situation of a strong TR-symmetry breaking\, so that\nCooper pairs entering the wire from the superconductor are immediately\ndestroyed. Nevertheless\, some traces of the proximity e ffect survive:\nfor example\, the local electronic density of states (LDOS ) is\ninfluenced by the proximity to the superconductor\, provided that\nl ocalization effects are taken into account. With the help of the\nsupersym metric sigma model\, we calculate the average LDOS in such a\nsystem. The LDOS in the wire is strongly modified close to the\ninterface with the sup erconductor at energies near the Fermi\nlevel. The relevant distances from the interface are of the order of\nthe localization length\, and the size of the energy window around the\nFermi level is of the order of the mean level spacing at the\nlocalization length. Remarkably\, the sign of the ef fect is sensitive\nto the way the TR symmetry is broken: In the spin-symme tric case\n(orbital magnetic field)\, the LDOS is depleted near the Fermi energy\,\nwhereas for the broken spin symmetry (magnetic impurities)\, the LDOS\nat the Fermi energy is enhanced. \n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. B. Rosenow DTSTART;TZID=Europe/Berlin:20121207T160000 DTEND;TZID=Europe/Berlin:20121207T171500 DTSTAMP:20260527T090436Z UID:0000000221@events.thp.uni-koeln.de DESCRIPTION:Prof. B. Rosenow\, Universität Leipzig\n\nNon-equilibrium ste ady states and charge fractionalization in Luttinger liquids\n\nIn many ca ses\, interacting fermions in one spatial dimension are described by the L uttinger model of free bosonic density excitations. Due to the absence of an interaction between these\nbosonic degrees of freedom\, the model is in tegrable. As a consequence\, it does not relax back to equilibrium when on e excites it via the local injection of electrons. Instead\, it reaches\na non-equilibrium steady state with a peculiar electronic distribution func tion and spectral density. In the case of two co-propagating chiral channe ls\, the non-perturbative method of\nnon-equilibrium bosonization allows t o characterize the electron distribution by a fractional Fano factor and i nterpret it in terms of charge fractionalization. \n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Silke Weinfurtner DTSTART;TZID=Europe/Berlin:20121214T160000 DTEND;TZID=Europe/Berlin:20121214T173000 DTSTAMP:20260527T090436Z UID:0000000224@events.thp.uni-koeln.de DESCRIPTION:Dr. Silke Weinfurtner\, SISSA\, Trieste\n\nQuantum Gravity Lab oratory\n\nA major problem of quantum field theory in curved spacetime\,\n and quantum gravity more generally\, is the lack of sufficient\nobservatio nal and experimental guidance. To address this issue I am\nproposing to ex plore various phenomena of semi-classical gravity and\nquantum gravity in table-top experiments. The overall programme is\nbased on the existence of analogue gravity models for semi-classical\nquantum gravity\, demonstrati ng that certain effects predicted within\nquantum field theory in curved s pacetimes can be mimicked in\neasy-to-access physical systems\, such as fl uids and superfluids. In\naddition\, I will explore the possibility of ada pting the general\nprinciples underlying analogue gravity models to full q uantum gravity\,\ncombining tools and concepts from quantum information th eory with\ndiscrete quantum gravity. In contrast to many other proposals i n\nquantum gravity\, the project objectives are not only theoretical\n(ana lytical and numerical studies)\, but also of experimental nature.\nThe sp ecific scientific goals are to study the robustness and\nuniversality of ( rotating) black hole phenomena in water channel\nflows\, cosmological part icle production in Bose-Einstein condensate\,\nand the emergence of a smoo th geometry as an ensemble average of\nbinary encodings of triangulated ma nifolds.\n\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. Pasquale Calabrese DTSTART;TZID=Europe/Berlin:20130111T160000 DTEND;TZID=Europe/Berlin:20130111T171500 DTSTAMP:20260527T090436Z UID:0000000237@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. Pasquale Calabrese\, Universität Pisa\n\nQuantum Qu enches in one dimensional systems\n\nNon-equilibrium quantum systems repre sent one of the most promising\npossibilities for realizing novel states o f matter. I will consider the non\nequilibrium situation known as quantum quench\, in which a closed system\nevolves from an initial state that is n ot a Hamiltonian eigenstate such as those\nachieved by suddenly switching a control parameter. An important question is\nunder what conditions the s ystem reaches a stationary state and in which\ncircumstances this state is characterized by an effective “thermal”\, i.e.\nequilibrium\, distrib ution. I will discuss how to obtain the time evolution of\nobservables and correlation functions with a variety of theoretical techniques\nincluding quantum field theory (in particular CFT) and integrability. These\napproa ches allow to have a rather complete understanding of the relaxation\ndyna mics and the most challenging open problems will be presented.\n\n\nContac t Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. Jan von Delft DTSTART;TZID=Europe/Berlin:20130118T160000 DTEND;TZID=Europe/Berlin:20130118T173000 DTSTAMP:20260527T090436Z UID:0000000240@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. Jan von Delft\, LMU München\n\nMicroscopic Origin o f the 0.7-Anomaly in Quantum Point Contacts\n\nQuantum point contacts are elementary building blocks of numerous\nsemiconducting nanodevices. Despit e their simple structure\, however\, their\nconductance properties exhibit anomalous features\, collectively known as the\n"0.7-anomaly"\, whose ori gin is still subject to controversial discussions. We\noffer a detailed mi croscopic explanation for the 0.7-anomaly and the zero-bias\npeak that typ ically accompanies it: the common origin of both is a smeared van\nHove si ngularity in the local density of states at the bottom of the lowest one-\ ndimensional subband of the point contact\, which causes an anomalous\nenh ancement in the Hartree potential barrier\, magnetic spin susceptibility a nd\ninelastic scattering rate. We present theoretical calculations and exp erimental\nresults that show good qualitative agreement for the dependence of the\nconductance on gate voltage\, magnetic field\, temperature\, sour ce-drain voltage\n(including the zero-bias peak) and interaction strength. For low energies we\npredict and observe Fermi-liquid behavior analogous to that known for the\nKondo effect in quantum dots. At high energies\, ho wever\, the analogy between\n0.7-anomaly and Kondo effect ceases to be app licable.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Johanna Erdmenger DTSTART;TZID=Europe/Berlin:20130412T163000 DTEND;TZID=Europe/Berlin:20130412T180000 DTSTAMP:20260527T090436Z UID:0000000247@events.thp.uni-koeln.de DESCRIPTION:Dr. Johanna Erdmenger\, Werner-Heisenberg-Institut München\n\ nGauge/Gravity Duality: New methods from string theory for strongly couple d systems\n\nWe give an introduction to the area of gauge/gravity duality and its\napplications. Based on string theory\, gauge/gravity duality maps strongly\ncoupled quantum field theories to weakly coupled gravity theori es and thus\nprovides a new framework for studying physical phenomena in s trongly\ncoupled systems. We describe the main features of this approach a nd\ndiscuss its range of applicability. Moreover\, we give examples of\nap plications in both elementary particle/nuclear physics and condensed\nmatt er physics. The examples presented include the quark-gluon plasma\,\nmeson s\, quantum phase transitions as well as superfluids and\nsuperconductors. \n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Stefan Scheel DTSTART;TZID=Europe/Berlin:20130419T163000 DTEND;TZID=Europe/Berlin:20130419T180000 DTSTAMP:20260527T090436Z UID:0000000242@events.thp.uni-koeln.de DESCRIPTION:Prof. Stefan Scheel\, Universität Rostock\n\nMacroscopic quan tum electrodynamics - quantum optics with macroscopic bodies\n\nIn this ta lk I will briefly review the basic principles of\nelectromagnetic field qu antisation in the presence of macroscopic\nmatter\, and explain its releva nce to the quantum interaction between\n(isolated) microscopic particles a nd macroscopic surfaces. As a first\nexample\, I will review some aspects of propagation of nonclassical light\nthrough absorbing optical devices. I will then concentrate on two\naspects of atom-surface interactions --- de coherence and dispersion\nforces (Casimir\, Casimir-Polder and van der Waa ls forces). Both effects\ncan be understood within the framework of macros copic QED as spatially\ndependent relaxation processes and line shift mech anisms\, respectively.\nI will present examples of highly excited atoms an d weakly bound\nmolecules that are particularly susceptible to changes in dispersion forces.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. F. Assaad DTSTART;TZID=Europe/Berlin:20130426T163000 DTEND;TZID=Europe/Berlin:20130426T173000 DTSTAMP:20260527T090436Z UID:0000000241@events.thp.uni-koeln.de DESCRIPTION:Prof. F. Assaad\, Universität Würzburg\n\nCorrelated topolog ical insulators\n\nThe interplay of spin-orbit coupling and correlations o pens a new \nplayground to study a variety of effects ranging from helical \nLuttinger liquids to quantum spin systems generated by threading \npi-fl uxes through correlated topological insulators. In this talk\, \nI will co ncentrate on the Kane-Mele model supplemented by a Hubbard \nU. After disc ussing the salient features of the non-interacting \nmodel - topological i nvariants and edge states - I will concentrate\non the above mentioned cor relations driven effects. The results \nobtained are based on large scale quantum Monte Carlo simulations \nwhich turn out to be free of the infamou s sign problem for this \nspecific class of models. \n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Bartlomiej Waclaw DTSTART;TZID=Europe/Berlin:20130503T163000 DTEND;TZID=Europe/Berlin:20130503T180000 DTSTAMP:20260527T090436Z UID:0000000243@events.thp.uni-koeln.de DESCRIPTION:Dr. Bartlomiej Waclaw\, University of Edinburgh\n\nPhysics in the evolution of microbes\n\nBiological evolution is a fascinating subject which can be fully understood\nonly if it is approached from many differe nt angles. In this talk I will\npresent my personal point of view on how p hysics can advance our\nunderstanding of biological evolution. I will focu s on three problems in the\nevolution of bacteria I have been working on r ecently. I will begin with a\nsimple\, statistical-physics model of the ev olution of antibiotic resistance.\nThis is a timely and important problem because drug-resistant\, pathogenic\nbacteria are becoming a major health hazard. I will show that resistant\nbacteria can rapidly emerge in environ ments with spatially non-uniform drug\nconcentration such as our bodies du ring antibiotic treatment. Towards the\nend of my talk\, I will briefly di scuss the evolution of metabolic networks\nin bacteria and biological evol ution in bacterial colonies growing on solid\nsubstrates.\n\n\nContact Per son: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. M. Troyer DTSTART;TZID=Europe/Berlin:20130607T163000 DTEND;TZID=Europe/Berlin:20130607T173000 DTSTAMP:20260527T090436Z UID:0000000254@events.thp.uni-koeln.de DESCRIPTION:Prof. M. Troyer\, ETH Zürich\n\nQuantum annealing on five hun dred qubits?\n\nQuantum technology is maturing to the point where quantum devices\,\nsuch as quantum communication systems\, quantum random number \ ngenerators and quantum simulators\, may be built with powers \nexceeding the performance of classical computers. A quantum \nannealer\, in particul ar\, finds solutions to hard optimization \nproblems by evolving a known i nitial configuration towards the \nground state of a Hamiltonian that enco des an optimisation \nproblem. In this talk I will present results from ex periments \non a 108 qubit D-Wave One device based on superconducting flux \nqubits and will provide evidence that the device indeed performs \nquan tum anealing. To assess the computational power of the \nquantum annealer I compare it to optimised classical algorithms \nand will present first pr eliminary results for a D-Wave Two \nsystem with more than five hundred qu bits.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Debashish Chowdhury DTSTART;TZID=Europe/Berlin:20130614T163000 DTEND;TZID=Europe/Berlin:20130614T180000 DTSTAMP:20260527T090436Z UID:0000000249@events.thp.uni-koeln.de DESCRIPTION:Prof. Debashish Chowdhury\, Indian Institute of Technology\, Kanpur\n\nStochastic kinetics of a self-organized complex molecular machin e: microtubule-chromosome coupling by ring-rod-hook device\n\nBefore cell division\, two identical copies of chromosome need to\nbe segregated accur ately. Each chromosome is connected to a "nano-ring"\n(dam1) by "rods" (Nd c80). For accurate chromosome segregation\, the two\nchromosomes are pulle d apart in the opposite directions by two sets of\n"nano-hooks"\, formed b y microtubules (MTs)\, that are inserted into these\nrings. An externally applied tension can lead to detachment of the hooks\nfrom the ring\; the m ean lifetime of such an attachment is essentially a\nmean first-passage ti me. Recent pioneering in-vitro experiments with\nreconstituted nano hook- ring device established that the mean lifetimes of\nsuch attachments vary non-monotonically with increasing tension. In this\ntalk I'll explain the counter-intuitive stabilization of the attachments by\nsmall tension with a unified model that we have developed very\nrecently. The catch-bond-lik e mechanism emerges naturally in this model\nfrom the interplay of tension -dependence of (i) the potential landscape and\n(ii) MT depolymerization r ate. I'll also show how the distribution of\nlifetimes of the hook-ring at tachment depends on (a) the structure\, (b)\nenergetics\, and (c) kinetics of the coupling.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. Florian Marquardt DTSTART;TZID=Europe/Berlin:20130621T163000 DTEND;TZID=Europe/Berlin:20130621T180000 DTSTAMP:20260527T090436Z UID:0000000262@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. Florian Marquardt\, Universität Erlangen-Nürnberg\ n\nDynamics of optomechanical arrays\n\nOptomechanical systems\, that coup le light to nanomechanical motion\,\nhave seen rapid progress during the p ast few years and have now\nentered the quantum regime of motion. In addit ion\, it is now\nbecoming possible to build optomechanical arrays\, i.e.\n arrays of many interacting localized optical and mechanical modes.\nThis o pens up several new areas for optomechanical systems\,\nsuch as quantum in formation processing with many mechanical modes\,\ncollective dynamics\, a nd quantum simulations.\nIn this talk I will focus on the nonlinear collec tive dynamics in such arrays.\nIn the classical regime\, mechanical oscill ations\ncan synchronize. The evolution of the mechanical oscillation\nphas e field can display interesting phenomena\, such as vortices.\nThe transit ion from the incoherent regime to a synchronized regime\ncan be determined either by static disorder or by noise.\nIn particular\, I will describe w hat happens under the influence\nof quantum noise.\n\n\nContact Person: no t specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Tobias Galla DTSTART;TZID=Europe/Berlin:20130628T163000 DTEND;TZID=Europe/Berlin:20130628T180000 DTSTAMP:20260527T090436Z UID:0000000264@events.thp.uni-koeln.de DESCRIPTION:Dr. Tobias Galla\, University of Manchester\n\nEffects of intr insic noise in individual-based systems\n\nInteracting particle systems in biology\, chemistry and the social sciences are\ntraditionally described by ordinary or partial differential equations. These\nare purely determini stic and based on the assumption that effects of noise can\nsafely be negl ected. Such approaches are no doubt chosen for their mathematical\nsimplic ity\, the theory of differential equations is well developed\, whereas\nex isting theories of non-equilibrium stochastic dynamics are more complex an d\nlargely incomplete. In this talk I will consider systems of a finite nu mber of\ninteracting particles\, their intrinsic stochasticity can then no longer be\nignored. I will discuss noise-induced phenomena such as quasi- cyles\,\nquasi-Turing patterns and travelling quasi waves\, and explain ho w they can be\ncharacterised analytically within the so-called linear nois e approximation.\nExamples where this is relevant include systems in evolu tionary dynamics\, game\ntheory and chemical reaction systems. One focus o f the talk will be on models\nwith delay dynamics\, important for example in gene regulatory systems or in\nepidemiology. I will show how path-integ ral approaches can be used to derive\ngeneral results for their chemical L angevin equation and linear-noise\napproximation.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. Reinhold Egger DTSTART;TZID=Europe/Berlin:20130705T163000 DTEND;TZID=Europe/Berlin:20130705T180000 DTSTAMP:20260527T090436Z UID:0000000265@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. Reinhold Egger \, Heinrich-Heine Universität Düsse ldorf \n\nMesoscopic transport properties of multiterminal Coulomb Majoran a junctions\n\nIn this talk\,‭ ‬the low-energy quantum transport prope rties of the Coulomb-Majorana junction‭ ‬will be discussed\,‭ ‬whe re several helical nanowires are coupled to a joint mesoscopic superconduc tor with finite charging energy.‭ ‬By virtue of the proximity effect\, ‭ ‬Majorana bound states are formed near the ends of the superconducti ng wire parts\,‭ ‬which are coupled together by charging effects.‭ F or sufficiently weak but finite charging energy\,‭ ‬this system generi cally approaches an isotropic SO(M‭) ‬Kondo fixed point with non-Fermi liquid behavior observable in quantum transport observables such as the t emperature-dependent conductance tensor or the fluctuating current noise c orrelator.‭ ‬The latter quantities follow from the Keldysh formulatio n of an effective phase action approach.‭ \n\nContact Person: not specif ied LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. V. L. Pokrovsky DTSTART;TZID=Europe/Berlin:20130719T163000 DTEND;TZID=Europe/Berlin:20130719T180000 DTSTAMP:20260527T090436Z UID:0000000260@events.thp.uni-koeln.de DESCRIPTION:Prof. V. L. Pokrovsky\, Texas A&M University\n\nCoherence and reflection symmetry breaking in the Bose-Einstein condensate of spin waves \n\nIn 2006 the phenomenon of Bose-Einstein condensation at room temperatu re was discovered in a ferromagnet YIG (Yttrium-Iron garnet) by the group of experimenters from University of\nMünster leaded by S. Demokritov. Th ey also presented a theoretical explanation of their experiment. In my tal k I will first describe this experiment and its explanation. Recently (Jun e\n2012) the same group discovered a low-contrast interference pattern in the intensity of Brillouin light scattering. The spectrum of spin waves in a thin film of YIG has two minima at\nfinite values of momentum + Q and - Q. The interference demonstrates that the two condensates have very differ ent densities despite complete symmetry of the system to space inversion. In\nour work (Fuxiang Li\, W.M. Saslow and V.L. P.) we propose a theory ex plaining why and how this symmetry is violated. Our theory predicts that i n thinner films it is possible to observe a\nsymmetric state of condensate s. The transition between these two states can be driven by magnetic field . The theory also predicts a new type of the collective oscillations. The dipolar\ninteraction plays a special role trapping the sum of the two cond ensate phases at the values 0 or pi. Transition between these two states i s possible in non-symmetric phase and can be\nobserved as a cusp in the pl ot of contrast vs. magnetic field.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Anatoly Konechny DTSTART;TZID=Europe/Berlin:20131018T163000 DTEND;TZID=Europe/Berlin:20131018T173000 DTSTAMP:20260527T090436Z UID:0000000270@events.thp.uni-koeln.de DESCRIPTION:Anatoly Konechny\, Heriot-Watt University\, Edinburgh\n\nBound ary entropy and its properties\n\nBoundary entropy of boundaries in one-d imensional critical systems was defined by I. Affleck and A. Ludwig in 199 1. A classic example of such systems is a conduction defect at low tempera ture as described by the Kondo model.\n\nBoundary entropy has a number of peculiar properties\, for example it can be negative.\n\nIn this talk we w ill discuss how this quantity is defined and what are its known properties .\n\nContact Person: Thomas Quella LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Rochus Klesse DTSTART;TZID=Europe/Berlin:20131025T163000 DTEND;TZID=Europe/Berlin:20131025T180000 DTSTAMP:20260527T090436Z UID:0000000271@events.thp.uni-koeln.de DESCRIPTION:Dr. Rochus Klesse\, University of Cologne\, Institute for Theo retical Physics\n\nProbability assignment and maximum entropy principles\n \nThe assignment of adequate probabilities to the basic\noutcomes of some random experiment under consideration is a\nprerequisite of a probabilisti c description. The maximum entropy\nprinciple of Statistical Mechanics sol ves this problem by stating that\namong all probability distributions that satisfy some given constraints\nthe one of maximum Boltzmann-Gibbs-Shanno n entropy must be chosen.\nBeing an indisputable principle of Statistical Mechanics\,\nits status outside physics as a general method of statistical \ninference is less clear.\n\nWe present a foundation of the maximum entro py principle that is based\non probabilistic arguments. It deliberately a voids reference to\nnotions of information and it does not appeal to physi cally motivated\nproperties of entropy. This is achieved by formalizing pr obability\nassignment as a certain symmetric\, continuous mapping that add itionally\nsatisfies a condition of self-consistency. We show that any suc h mapping\ncan be expressed as a variational principle\, i.e. as a general ized\nmaximum entropy principle with an a priori unspecified entropy funct ion.\nAdding a condition of statistical independence\, an earlier result o f\nShore and Johnson shows that the entropy function must be essentially\n the standard Boltzmann-Gibbs-Shannon entropy.\n\n\nContact Person: not spe cified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Peter Wölfle DTSTART;TZID=Europe/Berlin:20131129T163000 DTEND;TZID=Europe/Berlin:20131129T173000 DTSTAMP:20260527T090436Z UID:0000000296@events.thp.uni-koeln.de DESCRIPTION:Peter Wölfle\, KIT\n\nCritical fermionic quasiparticles near quantum critical points of antiferromagnetic metals\n\nA theory of the sca ling behavior of the thermodynamic\, transport and \ndynamical properties of a three-dimensional metal at an \nantiferromagnetic (AFM) critical poin t is presented. It is show how\nthe critical spin fluctuations at the AFM wavevector q = Q induce energy \nfluctuations at small q\, giving rise to a diverging quasiparticle \neffective mass over the whole Fermi surface. T he coupling\nof the fermionic and bosonic degrees of freedom leads to a \n self-consistent relation for the effective mass\, which has a strong \ncou pling solution in addition to the well-known weak-coupling \nspin-density wave solution. We thereby use the recently introduced \nconcept of critica l quasiparticles\, employing a scale dependent \neffective mass ratio m*/m and quasiparticle weight factor Z. We \nspecifically assume a scale depen dent vertex correction boosting the \ncoupling of fermions and spin fluctu ations. The ensuing spin fluctuation \nspectrum obeys E/T-scaling. Our res ults are in good agreement with\nexperimental data on the heavy fermion co mpounds YbRh2Si2 and CeCu6-xAux \nassuming 3D and 2D spin fluctuations\, r espectively.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. Florian Marquardt DTSTART;TZID=Europe/Berlin:20131206T163000 DTEND;TZID=Europe/Berlin:20131206T180000 DTSTAMP:20260527T090436Z UID:0000000308@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. Florian Marquardt\, Universität Erlangen-Nürnberg\ n\nPhotons and phonons interacting on a lattice\n\nNanomechanical structur es can be coupled to light in order\nto control their mechanical vibration s. Recent experimental developments\nin this field of "cavity optomechanic s" have led to\nlaser-cooling of such vibrations to their quantum ground s tate\nand entanglement between mechanics and the radiation field.\nA parti cularly promising platform consists in photonic crystal\nstructures with o ptical and vibrational modes localized at\ndefect sites. If these sites we re to be arranged periodically\,\nthey would form an "optomechanical array " that can be described via\na tight-binding model of interacting photons and phonons.\nI will describe our theoretical predictions\, including\nlig ht-induced synchronization of mechanical oscillators\,\nquantum many-body dynamics of photons and phonons\,\nDirac physics on an optomechanical hone ycomb lattice\, and\nthe possibility of generating artificial photonic gau ge fields.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Christian Maes DTSTART;TZID=Europe/Berlin:20131213T163000 DTEND;TZID=Europe/Berlin:20131213T180000 DTSTAMP:20260527T090436Z UID:0000000304@events.thp.uni-koeln.de DESCRIPTION:Prof. Christian Maes\, KU Leuven\n\nFluctuations determining r esponse in nonequilibrium systems\n\nIn or close-to-equilibrium response t o external stimuli and statistical forces are primarily entropic and gove rned by the standard thermodynamic potentials.\nWe report on a program of identifying a unifying kinetic feature\, called the frenetic contribution\ , to complement entropy considerations in the study of\nnonequilibrium beh avior. We therefore present extensions of the first and second fluctuation -dissipation relation for driven systems or for probes in contact with non equilibrium\n(active) baths.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Jacobus Verbaarschot DTSTART;TZID=Europe/Berlin:20140110T163000 DTEND;TZID=Europe/Berlin:20140110T173000 DTSTAMP:20260527T090436Z UID:0000000320@events.thp.uni-koeln.de DESCRIPTION:Prof. Jacobus Verbaarschot\, Stony Brook University\n\nDirac S pectra\, Tail States and Spontaneous Symmetry Breaking\n\nBecause of spont aneous symmetry breaking and a mass gap\, Dirac spectra \nshow universal b ehavior that can be understood by means of random matrix \ntheory. We dis cuss the effect of a nonzero lattice spacing on QCD \nDirac spectra and find tail states that have been observed before \nin disordered condensed matter systems. Despite the Coleman-Mermin-Wagner \ntheorem Dirac spectra also show universal behavior in two dimensions\, \nbut the unversality cl asses are different from those in four dimensions\nand depend on the pari ty of the lattice. A complete classification \nof two dimensional lattice QCD Dirac spectra in terms of the ten fold \nclassification of random matr ix theories is given.\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. Andreas Läuchli DTSTART;TZID=Europe/Berlin:20140117T163000 DTEND;TZID=Europe/Berlin:20140117T180000 DTSTAMP:20260527T090436Z UID:0000000321@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. Andreas Läuchli\, Universität Innsbruck\n\nEntangl ement spectra: A novel spectroscopic tool to investigate quantum many body wave functions\n\nThe entanglement spectrum\, i.e. the logarithm of the e igenvalues of reduced density matrices of \nquantum many body wave functio ns\, has been the focus of a rapidly expanding research endeavor recently. Initially introduced by Li & Haldane in the context of the fractional qua ntum Hall effect\, its usefulness has been shown to extend to many more fi elds\, such as topological insulators\, fractional Chern insulators\, spin liquids\, continuous symmetry breaking states\, etc. After a general intr oduction to the field we review some of our own contributions to the field \, in particular the perturbative structure of the entanglement spectrum i n gapped phases\, the entanglement spectrum across the Mott-insulator tran sition in the Bose-Hubbard model\, and the relation of the entanglement sp ectrum of (1+1) dimensional quantum critical systems to the operator cont ent of their underlying CFT.\n\n\nContact Person: Simon Trebst LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. Piet Brouwer DTSTART;TZID=Europe/Berlin:20140124T163000 DTEND;TZID=Europe/Berlin:20140124T180000 DTSTAMP:20260527T090436Z UID:0000000333@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. Piet Brouwer\, FU Berlin\n\nDisordered Majorana wire s\n\nA one dimensional spinless p-wave superconductor may be in a topologi cal nontrivial state\, in which it has a zero energy Majorana bound state at each end. Although no known materials are spinless p-wave superconducto rs\, such a system can be realized in principle in spin-orbit coupled nano wires with proximity-induced pairing from a nearby s-wave superconductor. After introducing the topological phase\, I will discuss how non-idealitie s\, such as potential disorder and deviations from a strict one-dimensiona l limit\, affect the topological phase and its signatures in a current-vol tage measurement.\n\n\nContact Person: Alexander Altland LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. Peter Grassberger DTSTART;TZID=Europe/Berlin:20140131T163000 DTEND;TZID=Europe/Berlin:20140131T180000 DTSTAMP:20260527T090436Z UID:0000000334@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. Peter Grassberger\, Jülich Supercomputing Centre\n\ nCooperativity in complex epidemics\n\nThere are two standard "Ising" mode ls for the spreading of epidemics\, the "SIS" (susceptible-infected-suscep tible) epidemic and the "SIR" (susceptible-infected-removed) model. Both a re related to percolation - the first to directed\, the second to undirect ed - and thus both show continuous ("second-order") phase transitions when the conditions for spreading are critical. Recently\, much interest has b een roused by models which show first order transitions. After giving a sh ort overview I will concentrate on first order transitions in models with cooperativity. This cooperativity can be of two very different types. On t he one hand\, several agents on neighboring nodes in a network (or sites o n a lattice) can cooperate in infecting a new node (like three friends who convince you more easily than any single one of them to adopt a political opinion). On the other hand\, also two pathogens (like HIV and TB) can co operate in the sense that one of them lowers the resistance to the other. In the first case the transition from a continuous to a discontinuous phas e transition is a standard tricritical point (with higher n-point interact ions in a field theoretic formalism)\, while in the second one one has a m ulti-component order parameter. In several instances\, the resulting first order transitions are actually "hybrid"\, i.e. they involve also features of second-order transitions like scaling. In one case\, one even finds th at two order parameter definitions which coincide for ordinary percolation display different transition orders.\n\nContact Person: Joachim Krug LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Prof. Dr. Jens Eisert DTSTART;TZID=Europe/Berlin:20140207T163000 DTEND;TZID=Europe/Berlin:20140207T180000 DTSTAMP:20260527T090436Z UID:0000000332@events.thp.uni-koeln.de DESCRIPTION:Prof. Dr. Jens Eisert\, FU Berlin\n\nTaming the non-equilibriu m\n\nComplex quantum systems out of equilibrium are at the basis of a\n number of the most intriguing puzzles in physics. This talk will be\n concerned with recent progress on understanding how quantum many-body\ n systems out of equilibrium eventually come to rest and thermalise. The\n first part of the talk will highlight theoretical progress on t his\n question\, taking in several ways a quantum information view -\ n employing ideas of Lieb-Robinson bounds\, quantum central limit\n theorems and of concentration of measure. These findings will be\n complemented by experimental work with ultra-cold atoms in optical\n lattices\, in setups constituting dynamical "quantum simulators"\,\n allowing to probe physical questions that are not only out of reach\n for state-of-the-art numerical techniques based on matrix-product\n states\, but also relate to classically computationally hard problems.\n \n\nContact Person: Alexander Altland LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Matthias Sperl DTSTART;TZID=Europe/Berlin:20140411T163000 DTEND;TZID=Europe/Berlin:20140411T180000 DTSTAMP:20260527T090436Z UID:0000000449@events.thp.uni-koeln.de DESCRIPTION:Dr. Matthias Sperl\, DLR Cologne\n\nNon-Equilibrium Dynamics i n Granular Matter\n\nThe dynamics in granular matter is inherently out-of- equilibrium\, as \ntime-reversal symmetry is broken by the energy loss dur ing interparticle \ncollisions. This presents challenges to both theory an d experiment: \nExperimentally\, granular systems need to be agitated stro ngly to achieve \nsteady states or need to be measured in microgravity to avoid sedimentation. \nFor the theoretical treatment\, suitable ensembles need to be assumed or \ninferred from experiments.\n\nExperiments from par abolic-flight and drop-tower campaigns shall be shown for \nthe dilute reg ime of granular gases where homogeneous steady states and \ngranular cooli ng are observed. For dense granular fluids\, the derivation of \ngranular rheology from first principles shall be presented as well as new \nexperim ental techniques for the characterization of granular states such as \nX-r ay radiography and tomography\, and terahertz scattering.\n\n\nContact Per son: Joachim Krug LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | M. Lässig DTSTART;TZID=Europe/Berlin:20140425T163000 DTEND;TZID=Europe/Berlin:20140425T173000 DTSTAMP:20260527T090436Z UID:0000000470@events.thp.uni-koeln.de DESCRIPTION:M. Lässig\, Institut für Theoretische Physik\, Universität zu Köln\n\nEvolution of influenza: Statistical genetics far from equilibr ium\n\nThe human flu virus undergoes rapid evolution\, which is driven by interactions with its host immune system. We describe the evolution of vir al genomes in terms of a non-equilibrium statistical mechanics model. This model successfully predicts the evolution of influenza one year into the future. Thus\, evolutionary analysis transcends its traditional role of re constructing past history. This has important consequences for public heal th: evolutionary predictions can inform the selection of influenza vaccine strains. We discuss the conditions of predictability and its links to coo perative phenomena and universality. These links highlight the key role of statistical mechanics in making evolutionary biology a predictive science .\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dr. Regine Frank DTSTART;TZID=Europe/Berlin:20140509T163000 DTEND;TZID=Europe/Berlin:20140509T180000 DTSTAMP:20260527T090436Z UID:0000000463@events.thp.uni-koeln.de DESCRIPTION:Dr. Regine Frank\, Eberhard Karls Universität Tübingen\n\nSi gnatures of Anderson Localization of Light in Real World Disordered Sample s\n\nTo derive Anderson localization of light is one of the holy grails of our time. I show in this talk theoretical results derived by Vollhardt-W ölfle theory of photons in a novel time dependent approach. The results a re given for 3D disordered\, finite sized real world systems of poly-dispe rse powders consisting of TiO_2 Mie spheres. Signatures of  Anderson loca lized states\, namely interference effects\, are determined and they can b e clearly distinguished from long living light-matter bound states as well as frequency converted photons and losses. Influences of different types of non-linear effects are discussed.\n\nContact Person: Alexander Altland LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Philipp Werner DTSTART;TZID=Europe/Berlin:20140516T163000 DTEND;TZID=Europe/Berlin:20140516T173000 DTSTAMP:20260527T090436Z UID:0000000480@events.thp.uni-koeln.de DESCRIPTION:Philipp Werner\, Fribourg\n\nDynamical mean field approach to correlated lattice systems in and out of equilibrium\n\nOver the past 25 y ears\, the dynamical mean field (DMFT) formalism has been extended from fe rmionic Hubbard-type models to realistic multi-band materials\, bosonic la ttice systems and even quantum field theories. It has also been developed into a powerful and versatile tool for the study of nonequilibrium phenome na in correlated lattice models. I will provide an overview of the key dev elopments in the field and explain the most recent addition to the DMFT fa mily - the DMFT treatment of quantum field theories. In the second part of the talk I will discuss two predictions from nonequilibrium DMFT studies: the possibility to switch the Coulomb repulsion into an effective attract ive interaction through the application of periodic electric fields\, and the existence of nonthermal critical points\, which control the relaxation dynamics of the antiferromagnetic or superconducting order parameter on i ntermediate time-scales.\n\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Tim Wehling DTSTART;TZID=Europe/Berlin:20140523T163000 DTEND;TZID=Europe/Berlin:20140523T173000 DTSTAMP:20260527T090436Z UID:0000000488@events.thp.uni-koeln.de DESCRIPTION:Tim Wehling\, Universität Bremen\n\nElectronic structure of l ow dimensional materials: from graphene to quantum impurities\n\nLow dimen sional structures combine pronounced surface effects with distinct\nmany b ody interactions. Both affect material properties decisively\, as they\nde termine excitations and boundaries between different electronic as well as \nstructural phases. Here\, we discuss how the electronic structure of low \ndimensional materials can be understood based on microscopic theory alon g\nwith three examples of how interactions affect material properties. Fir st\, we\nconsider chemically functionalized graphene and show how doping t riggers\nadsorbate phase transitions including tendencies towards sublatti ce symmetry\nbreaking. Regarding the electrons in layered materials\, loca l "Hubbard\ninteractions" generally compete with large non-local Coulomb i nteractions. We\nwill discuss the "two-faced" nature of these non-local in teractions: while they\ncontribute to strong renormalizations of electroni c excitations\, non-local\nCoulomb terms turn out to weaken ground state e lectronic correlations\nfrequently. Finally\, we will turn to quantum impu rity problems and show how\nelectronic interactions shape excitation spect ra in magnetic nanostructures.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | David Gross DTSTART;TZID=Europe/Berlin:20140606T160000 DTEND;TZID=Europe/Berlin:20140606T173000 DTSTAMP:20260527T090436Z UID:0000000489@events.thp.uni-koeln.de DESCRIPTION:David Gross\, Universität Freiburg\n\nQuantum cellular automa ta\, the Pauli principle\, and vintage movies\n\nThe output files of a dig ital camera are typically only 10% the size of the raw data.\nCan one desi gn a physical process that only records the relevant information to\nbegin with? The recently developed field of "compressed sensing" achieves this\ ntrick for certain signals. Building on tools from mathematical physics\, we have\nintroduced new methods to the theory which have since found appli cations in\nareas as diverse as face recognition\, despeckling of movie fr ames\, and large\ndeviation bounds for non commutative processes.\nIn a se cond\, unrelated part\, I will talk about the one-body quantum marginal\np roblem. Here\, the task is to decide which set of local reduced density ma trices\nare compatible with a globally pure state. Known to be non-trivial since the 70s\,\nonly recent developments in symplectic geometry and asym ptotic representation\ngeometry have made the problem tractable. I will re port on our work that connects\nthese methods to the study of multi-partit e entanglement and fermionic many-body\nsystems.\nLastly\, I will mention some results related to the classification of time evolutions in\ndiscrete quantum lattice systems (otherwise known as quantum cellular\nautomata).\ n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Sebastian Diehl DTSTART;TZID=Europe/Berlin:20140620T160000 DTEND;TZID=Europe/Berlin:20140620T173000 DTSTAMP:20260527T090436Z UID:0000000490@events.thp.uni-koeln.de DESCRIPTION:Sebastian Diehl\, Universität Innsbruck\n\nAspects of Univers ality in Driven Open Quantum Systems\n\nRecent experimental developments i n diverse areas - ranging from cold atomic\ngases over light-driven semico nductors to microcavity arrays - move systems\ninto the focus\, which are located on the interface of quantum optics\, many-body\nphysics and statis tical mechanics. They share in common that coherent and\ndriven-dissipativ e quantum dynamics occur on an equal footing\, creating\nscenarios without immediate counterpart in condensed matter. A key challenge\nis to identif y universal macroscopic phenomena\, which manifestly witness\nmicroscopic non-equilibrium conditions.\nHere\, we will report on three results in thi s direction. First\, we show that\ndynamical Bose criticality in driven sy stems lies beyond the equilibrium Halperin-\nHohenberg classification. Sec ond\, we argue that driven open systems in two\ndimensions\, realized by e nsembles of exciton-polaritons\, cannot support\nsuperfluidity and quasi-l ong range order. Third\, we reveal new\, manifestly non-\nequilibrium scal ing behavior in the short time heating dynamics of interacting\,\nultracol d atomic quantum wires.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Jie Ren DTSTART;TZID=Europe/Berlin:20140627T160000 DTEND;TZID=Europe/Berlin:20140627T173000 DTSTAMP:20260527T090436Z UID:0000000491@events.thp.uni-koeln.de DESCRIPTION:Jie Ren\, Massachusetts Institute of Technology\n\nSpin Seebec k diode and transistor: smart control of energy and information in nano-de vices\n\nEnergy waste is a severe bottleneck in the supply of sustainable energy to any\nmodern economy. Besides developing new energy sources\, the global energy\ncrisis can be alleviated by re-utilizing the waste heat. I n this talk\, I will first\nintroduce some background of harnessing the th ermal energy by the\nthermoelectrics\, spin caloritronics\, and phononics. Then\, in the second part\, I\nwould like to share with you some of my re cent discoveries about the\nrectification and negative differential spin S eebeck effects\, exemplified in\nmetal/magnetic insulator interfaces and m agnon tunneling junctions. These\nproperties lead us to the novel devices\ , such as thermal-driven spin diode and\ntransistor in the absence of elec tric transports. I call them spin Seebeck diode\nand transistor. These fin dings imply that a spin computer driven by waste heat\nmight not be a drea m in the future\, which offer us new opportunities to achieve\nthe smart c ontrol of energy and information at nanoscale.\n\n\nContact Person: not sp ecified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Maria Hermanns DTSTART;TZID=Europe/Berlin:20140704T160000 DTEND;TZID=Europe/Berlin:20140704T170000 DTSTAMP:20260527T090436Z UID:0000000492@events.thp.uni-koeln.de DESCRIPTION:Maria Hermanns\, University of Cologne\n\nMajorana metals and quantum spin liquids\n\nOne of the most intriguing phenomena in strongly c orrelated systems is\nthe fractionalization of quantum numbers - familiar examples include \nthe spin-charge separation in one-dimensional metallic systems\, \nthe fractionalization of the electron in certain quantum Hall states \nor the emergence of monopoles in spin ice.\n\nIn this talk\, I wi ll discuss the fractionalization of magnetic \nmoments in a certain class of Mott insulators\, in which the emergent \ndegrees of freedom are Majora na fermions that form an (almost) \nconventional metal. The origin of such a dichotomous state is \nelucidated by a family of exactly solvable model s of frustrated \nquantum magnets in three dimensions\, which might be rea lized in \na class of recently synthesized Iridate compounds. These models \nthereby provide the first analytical tractable examples of long \nsough t-after quantum spin liquids with a spinon Fermi surface and \neven an ent ire new class of quantum spin liquids - a so-called Weyl \nspin liquid\, i n which the fractionalized degrees of freedom form \na topological semi-me tal.\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | U. Gerland DTSTART;TZID=Europe/Berlin:20141107T163000 DTEND;TZID=Europe/Berlin:20141107T173000 DTSTAMP:20260527T090436Z UID:0000000549@events.thp.uni-koeln.de DESCRIPTION:U. Gerland\, TU München \n\nSpatially orchestrated enzyme kin etics in multi-enzyme complexes\n\nTo efficiently catalyze multi-step bioc hemical reaction pathways\, cells have\noptimized the synergistic action o f a multitude of enzymes. They not only\ncontrol the concentrations and ac tivities of enzymes\, but often also\ncoordinate enzymes from the same bio chemical reaction pathway by arranging\nthem in self-assembled multi-enzym e complexes. Such complexes are the basis\nof `channeling' mechanisms\, wh ere intermediate products in multi-step \nreactions are effectively passed from one enzyme to the next. These\nsame principles can be applied in art ificial nano-scale systems\, \nwith the ultimate goal to control and optim ize biochemical reactions \nat will\, e.g. for the production of medical s ubstances or renewable \nenergy sources. While enzymatic activity has been studied for over \na century\, quantitative experiments were limited to t he bulk level \nuntil the recent advent of single-molecule enzymology tech niques\, \nwhich permit the quantitative characterization of the stochasti c \nreaction dynamics of enzymes. Single-molecule experiments with \nenzym es have also spurred the theoretical analysis of stochastic \nenzyme dynam ics\, but the theoretical description and analysis of \nenzyme complexes i s only beginning to develop. I will describe \nsome recent progress in thi s direction.\n\n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | C. Kiefer DTSTART;TZID=Europe/Berlin:20141114T163000 DTEND;TZID=Europe/Berlin:20141114T173000 DTSTAMP:20260527T090436Z UID:0000000550@events.thp.uni-koeln.de DESCRIPTION:C. Kiefer\, Institut für Theoretische Physik\, Universität z u Köln\n\nObservations of gravitons from the early Universe?\n\nModern th eories of cosmology assume that the Universe underwent\na period of expone ntial expansion ("inflation") at an early stage.\nInflation does not only solve some of the conceptual problems of\nearlier cosmological models\, bu t also allows a causal explanation of\nstructure formation. Moreover\, it necessarily predicts the creation\nof gravitons\, the spin-2 particles ass ociated with the quantized\ngravitational field. In March 2014\, the south -pole experiment\nBicep2 announced the observational confirmation of such\ nprimordial gravitons.\nIf true\, this would constitute a major step towar ds an understanding\nof quantum gravity and the origin of our Universe.\nI n my talk\, I shall summarize the physics that is needed to understand\nth is result\, review the observations\, and give an outlook on future\ndevel opments. \n\n\nContact Person: not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | John Chalker DTSTART;TZID=Europe/Berlin:20141204T160000 DTEND;TZID=Europe/Berlin:20141204T170000 DTSTAMP:20260527T090436Z UID:0000000563@events.thp.uni-koeln.de DESCRIPTION:John Chalker\, Oxford University\n\nClassical loop models and quantum phase transitions\n\nI will give an overview of recent work on the physics of lattice models of\nclose-packed loops. The models have two pha ses -- one in which all loops\nare finite\, and another in which some loop s are extended -- and the\ninterest is in universal features of these phas es and the transitions \nbetween them. The models describe a number of pro blems in classical \nstatistical physics -- where\, for example\, the loop s may be vortex\nlines in a three-dimensional random field -- and also man y-body quantum\nsystems -- where the loops are world-lines of particles.\n \n\nContact Person: Alexander Altland LOCATION:TP Seminarraum END:VEVENT BEGIN:VEVENT SUMMARY:TPK | P. Strack DTSTART;TZID=Europe/Berlin:20141205T163000 DTEND;TZID=Europe/Berlin:20141205T173000 DTSTAMP:20260527T090436Z UID:0000000551@events.thp.uni-koeln.de DESCRIPTION:P. Strack\, Institut für Theoretische Physik\, Universität z u Köln\n\nInteracting and emergent photons in quantum optics and condense d matter\n\nRecent experimental developments in quantum optics have opened \nup possibilities to create strongly correlated states of matter with si zable \nelectromagnetic or photonic components. Enabled by strong atom-pho ton \ncoupling on the single-quantum level\, for example in cavity QED and with \nRydberg atoms\, it is now possible to study the statistical\, and generically \nfar-from-equilibrium\, physics of photons in new regimes far beyond \nwhat is know from the laser theory developed in the 1970's. Here \, I will \nsurvey our first attempts to classify such phases of photonic matter into \nuniversality classes including glasses\, superradiant Fermi gases\, and \nattractive quantum liquids.\nIn the second part\, I will con sider electronic materials in which \nfrustration and interactions are so strong that\, collective excitations \nmade out of electronic spins behave as emergent photons\, and compute \nnew observable signatures thereof.\nF urther information: http://www.thp.uni-koeln.de/~strack/\n\nContact Person : not specified LOCATION:Seminarraum Theoretische Physik END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Byungnam Kahng DTSTART;TZID=Europe/Berlin:20150109T163000 DTEND;TZID=Europe/Berlin:20150109T173000 DTSTAMP:20260527T090436Z UID:0000000552@events.thp.uni-koeln.de DESCRIPTION:Byungnam Kahng\, Seoul National University \n\nDiscontinuous p ercolation transitions in cluster merging processes\n\nRecently interest o f discontinuous percolation transitions (DPT) has been boosted in complex\ nsystems\, because the DPT can be found in many real-world systems such as epidemic\nspreading and cascading failures of inter-dependent infra-struc ture. Nevertheless\,\nmany fundamental questions remained unsolved yet. On e of them was to invent the model\nexhibiting the DPT in cluster merging p rocesses and to understand diverse properties arising\nin such models. In my talk\, I will present recent theoretical research progress of the DPT i n\nthe cluster merging processes\, which includes models\, properties of D PTs\, and future works.\n\nContact Person: not specified LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Christopher Mudry DTSTART;TZID=Europe/Berlin:20150116T163000 DTEND;TZID=Europe/Berlin:20150116T173000 DTSTAMP:20260527T090436Z UID:0000000554@events.thp.uni-koeln.de DESCRIPTION:Christopher Mudry\, Paul-Scherrer Institut\n\nAnderson localiz ation and the topology of classifying spaces\n\nWe deduce the generic phas e diagrams encoding the distinct\nlocalized and delocalized phases of noni nteracting fermionic quasiparticle\nfor any symmetry class from the tenfol d way in one\, two\, and three dimensions.\nTo this end\, we start from a massive Dirac Hamiltonian perturbed by\na generic disorder for any dimensi on of space and for any one of the ten\nsymmetry classes from the tenfold way. The physics of Anderson localization\nis then encoded by a two-dimens ional phase diagram that we deduce from\nthe topology of the space of norm alized Dirac masses.\n\nContact Person: not specified LOCATION:seminar room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | M. Fleischhauer DTSTART;TZID=Europe/Berlin:20150123T163000 DTEND;TZID=Europe/Berlin:20150123T173000 DTSTAMP:20260527T090436Z UID:0000000553@events.thp.uni-koeln.de DESCRIPTION:M. Fleischhauer\, Kaiserslautern\n\nMany-body physics in open systems: Rydberg gases and Rydberg polaritons\n\nQuantum optical realizati ons of many-body systems must often be considered\nas open systems and thu s offer a way to study quantum correlations and\nphase transitions in a no n-equilibrium steady-state. The competition between interactions and fluct uations inherent to an open system will be discussed for the experimentall y relevant examples of optically driven Rydberg gases and Rydberg polarito ns. The steady-state phase transition to crystalline order in a lattice ga ses will be discussed as well as the dynamics of its build-up.\nIn the sec ond part photons coupled to Rydberg atoms under conditions of electromagne tically induced transparency will be considered. The coupling results in s trongly interacting polaritons\, which behave like hard-sphere objects wit h non-local interaction giving rise to a non-local nonlinear optics.\n\n\n Contact Person: not specified LOCATION:seminar room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | D. Schuricht DTSTART;TZID=Europe/Berlin:20150130T163000 DTEND;TZID=Europe/Berlin:20150130T173000 DTSTAMP:20260527T090436Z UID:0000000571@events.thp.uni-koeln.de DESCRIPTION:D. Schuricht\, Utrecht\n\nTime evolution and relaxation in str ongly correlated quantum systems\n\nRecent experiments on the dynamics of ultra-cold atomic gases have opened up completely new ways to study far-fr om-equilibrium quantum states. These intriguing prospects triggered tremen dous experimental and theoretical developments and have led to an extremel y active research field. In particular\, strongly correlated quantum syste ms have been at the forefront of theoretical research since they show non- trivial many-body effects. I will give a brief overview over these develop ments with an emphasis on the dynamics of one-dimensional systems\, where the dynamics may be restricted by the existence of non-trivial integrals o f motion linking it to the field of integrable systems. I will then presen t results on the universality of the time evolution in both massive and ma ssless systems and discuss the effects of finite quench times.\n\nContact Person: not specified LOCATION:seminar room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Su-Chan Park DTSTART;TZID=Europe/Berlin:20150206T163000 DTEND;TZID=Europe/Berlin:20150206T180000 DTSTAMP:20260527T090436Z UID:0000000587@events.thp.uni-koeln.de DESCRIPTION:Su-Chan Park\, Catholic University of Korea \n\nWell-understoo d and ill-understood universality classes of absorbing state phase transit ions\n\nIn this talk\, various universality classes found in absorbing pha se transitions will be reviewed. Starting from the contact process\, the d irected percolation (DP) universality class and a possible classification scheme known as the DP conjecture will be discussed. The DP conjecture sta tes that a model system without nontrivial symmetry and/or conservation la ws and with a single order parameter field should belong to the DP class. Other universality classes have been found by breaking some of the requis ites of the DP conjecture\, which will be briefly discussed. Particular fo cus of this talk will be on a controversy around the universality class t o which the pair contact process with diffusion (PCPD) should belong. Two conflicting viewpoints and their supporting arguments will be reviewed. Endeavors to settle down this\ncontroversy will be discussed.\n\n\nContact Person: not specified LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dmitry Fedosov DTSTART;TZID=Europe/Berlin:20150410T163000 DTEND;TZID=Europe/Berlin:20150410T180000 DTSTAMP:20260527T090436Z UID:0000000639@events.thp.uni-koeln.de DESCRIPTION:Dmitry Fedosov\, Institute for Complex Systems\, FZ Jülich\n\ nMultiscale modeling of blood flow: From single cells to intricate multi-c ell interactions\n\nBlood flow plays an important role in many physiologic al processes and pathologies in the organism. To understand these processe s\, detailed investigation of blood flow is\nrequired under realistic cond itions including cell deformability\, hydrodynamic interactions\, and comp lex geometries. We employ the smoothed dissipative particle dynamics metho d\, a\nmesoscopic hydrodynamic simulation technique\, to model blood as a suspension of deformable cells represented by a viscoelastic spring-networ k which incorporates appropriate mechanical\nand rheological cell-membrane properties. Blood flow in idealized micro-channel geometries will be inve stigated. We will discuss the physical mechanisms which govern migration o f micro-\nand nano-carriers toward the walls in micro-vessels. Moreover\, we will present the flow behavior of blood cells in a microfluidic device which offers great opportunities for cell\nsorting. We will illustrate the use of complex flow geometries to separate cells of different sizes and t he application of realistic blood flow simulations to optimize the device\ nperformance.\n\nContact Person: Joachim Krug LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Jens Elgeti DTSTART;TZID=Europe/Berlin:20150417T163000 DTEND;TZID=Europe/Berlin:20150417T180000 DTSTAMP:20260527T090436Z UID:0000000640@events.thp.uni-koeln.de DESCRIPTION:Jens Elgeti\, Institute for Complex Systems\, FZ Jülich\n\nSi mulating growing tissues\n\nGrowth of solid tumors or metastasis requiers\ , besides massive biomedical changes\, also a spatial remodeling of the ti ssue. This remodeling\, often including displacements of healthy tissue ar ound\, requires mechanical work to be done. These mechanics of growth has attracted a lot of attention in recent years\, but still remains poorly un derstood. We use particle based simulations to study mechanical properties and effects in growing and motile tissues. These simulations have been he lpful in understanding\, interpreting and designing experiments. I will p resent an overview of the simulation thechnique\, and how it contributed t o recent develobments in three dimensional tissue growth and collective ce ll migration. In a recent series of simulations and close experimental col laborations we found important interfacial and surface effects that lead t o novel phenomena. For example\, the tissue divides favorably at a free su rface\, even without any nutrient effects. This leads to the possibility a nd stability of a negative homeostatic pressure. In turn\, a negative home ostatic pressure leads to naturally to finite steady states and tensile st ates.\n\nContact Person: Joachim Krug LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Friedrich Hehl DTSTART;TZID=Europe/Berlin:20150424T163000 DTEND;TZID=Europe/Berlin:20150424T180000 DTSTAMP:20260527T090436Z UID:0000000634@events.thp.uni-koeln.de DESCRIPTION:Friedrich Hehl\, Institute for Theoretical Physics\, Cologne\n \nOn the metamorphoses of Maxwell's equations of electrodynamics since 186 5: spotlights on the history of classical electrodynamics\n\nStarting wit h Maxwell's equations for the electromagnetic field\n(1865)\, we first poi nt out how Maxwell brought his system of equations\ninto quaternionic form . Subsequently\, we recognize that what we call\nMaxwell's equations nowad ays is a creation of Heaviside and Hertz. Then\nwe study the impact of spe cial and of general relativity on Maxwell's\nequations. In particular we f ollow up the metric-free and topological\nversion of Maxwell's equations v ia exterior differential forms and\nperiod integrals and discuss some appl ications. Alternative\nformulations via spinors\, Clifford algebras\, chai ns and\ncochains... are shortly mentioned.\n\nContact Person: not specifie d LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Jens Bardason DTSTART;TZID=Europe/Berlin:20150508T163000 DTEND;TZID=Europe/Berlin:20150508T180000 DTSTAMP:20260527T090436Z UID:0000000650@events.thp.uni-koeln.de DESCRIPTION:Jens Bardason\, MPI-PKS Dresden\n\nMany-body localization\, en tanglement and natural orbitals\n\nIn this talk I will discuss how entangl ement and the eigenstates (natural orbitals) and eigenvalues (occupations) of the one-particle density matrix can be used to characterize the many-b ody localization transition and phases. Many-body localization is the inte racting version of the Anderson insulator\, and is reflected both as local ization of particles in real space\, as well as in Fock-space. The study o f entanglement\, both in eigenstates and its evolution after quenches\, ha s been instrumental in advancing our understanding of many-body localized phases. The entanglement entropy of eigenstates goes from an area law in t he localized phase\, reflecting the real space localization of wave functi ons\, to an volume law in the delocalized phase\, with diverging fluctuat ions at the transition. In contrast\, a global quench within the many-bod y localized phase gives rise to a slowly (logarithmically) increasing enta nglement entropy. The entropy of occupations in the one-particle density m atrix turns out to have similar properties as the entanglement entropy--ar ea law in localized phase\, volume law in delocalized phase\, and divergin g fluctuations at the transition--but this is reflecting the Fock space st ructure of the eigenstates. Finally\, the inverse participation ratio of t he natural orbitals can be used to define a one-particle localization leng th in the localized phase. \n\nContact Person: not specified LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Tomaz Prosen DTSTART;TZID=Europe/Berlin:20150515T163000 DTEND;TZID=Europe/Berlin:20150515T180000 DTSTAMP:20260527T090436Z UID:0000000631@events.thp.uni-koeln.de DESCRIPTION:Tomaz Prosen\, University of Ljubljana\n\nExact solutions of b oundary-driven quantum master equations and new conservation laws\n\nThe a nisotropic Heisenberg chain of spins 1/2 is one of the key paradigms of st rongly\ncorrelated electrons in one dimension. While equilibrium propertie s of the model\nare relatively well understood\, even very basic questions about its non-equilibrium\nproperties were still open until very recently . A prominent example is the question\nwhether the model exhibits ballisti c spin transport at finite temperatures or not?\nI will outline the progre ss on this topic which has been triggered by the discovery\nof exact solut ion of quantum master equation of the boundary driven Heisenberg\nchain. T he steady-state solution of non-equilibrium master equation leads\nto nove l quasi-local conservation laws\, which in turn lead to a derivation\nof r igorous strict lower bounds on ballistic transport coefficients. I will al so\nexplain how such an approach of `non-equilibrium integrability' works for some other\nstrongly interacting quantum chains\, for instance\, for t he Hubbard model or Lai-\nSutherland model of spins 1.\n\nContact Person: Vladislav Popkov LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Matthias Vojta DTSTART;TZID=Europe/Berlin:20150522T163000 DTEND;TZID=Europe/Berlin:20150522T180000 DTSTAMP:20260527T090436Z UID:0000000651@events.thp.uni-koeln.de DESCRIPTION:Matthias Vojta\, TU Dresden\n\nCoupled-dimer magnets: Systemat ic expansions\, quantum criticality\, and disorder\n\nCoupled-dimer magnet s have become model systems in the study of quantum phase transitions. Aft er a brief introduction to quantum criticality in magnets\, the talk will discuss various theoretical approaches to describe coupled-dimer magnets\, using both field-theoretic and microscopic techniques\, and link the resu lts to experimental observations. In particular\, a novel expansion in 1/d will be presented where d is spatial dimensionality. In addition\, intere sting phenomena arising from quenched disorder in coupled-dimer magnets wi ll be highlighted\, both for dilute and dense concentration of defects.\n\ nContact Person: Alexander Altland LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Eric Lutz DTSTART;TZID=Europe/Berlin:20150612T163000 DTEND;TZID=Europe/Berlin:20150612T180000 DTSTAMP:20260527T090436Z UID:0000000644@events.thp.uni-koeln.de DESCRIPTION:Eric Lutz\, University of Erlangen-Nürnberg\n\nThe physics of information: from Maxwell's demon to Landauer\n\nWe will discuss the inti mate connection existing between information theory and thermodynamics fol lowing its historical development. We will focus on two complementary aspe cts: 1) the gain of information which we will illustrate with Maxwell's fa mous demon and 2) the erasure of information summarized by Landauer's prin ciple. We will further present a number of recent single-particle experime nts that have for the first time realized the above gedanken experiments i n the lab.\n\n\nContact Person: Johannes Berg LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Shivaji Sondhi DTSTART;TZID=Europe/Berlin:20150619T163000 DTEND;TZID=Europe/Berlin:20150619T174500 DTSTAMP:20260527T090436Z UID:0000000626@events.thp.uni-koeln.de DESCRIPTION:Shivaji Sondhi\, Princeton\n\nMany Body Localization\n\nFamous ly\, Anderson showed in 1958 that non-interacting quantum mechanical elect rons placed in a\nrandom potential could fail to exhibit diffusion. In 200 5 Basko\, Aleiner and Altshuler put the long\nconjectured extension of the Anderson localization to the interacting setting\, termed Many Body\nLoca lization\, on a much firmer footing setting off a rapidly growing volume o f work on this\nphenomenon. I will describe the broad outlines of this wor k and discuss how it has both enriched our\nunderstanding of the foundatio n of quantum statistical mechanics and led to the remarkable\nnotion of no n-equilibrium quantum phase structure that lies outside the former.\n\nCon tact Person: Simon Trebst LOCATION:seminar room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Jürg Fröhlich DTSTART;TZID=Europe/Berlin:20150626T163000 DTEND;TZID=Europe/Berlin:20150626T180000 DTSTAMP:20260527T090436Z UID:0000000669@events.thp.uni-koeln.de DESCRIPTION:Jürg Fröhlich\, ETH Zürich\n\nDirect and Indirect Acquisiti on of Information in Quantum Mechanics\n\nIt is explained how\, in quantum mechanics\, information about a physical system is acquired through direc t (von Neumann) and indirect (Kraus) measurements/observations. In a first part\, a new theory of direct (projective\, or von Neumann) measurements is developed\, using methods and results from functional analysis. In a se cond part\, the theory of indirect measurements is sketched\, and it is sh own how various theorems from probability theory and statistics can be use d for this purpose. Many of the general ideas are explained in the context of a simple model system.\nTime permitting\, I will outline tentative app lications of the main ideas presented in this talk to a theory of percepti on.\n\n\nContact Person: Martin Zirnbauer LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Holger Gies DTSTART;TZID=Europe/Berlin:20150710T163000 DTEND;TZID=Europe/Berlin:20150710T173000 DTSTAMP:20260527T090436Z UID:0000000683@events.thp.uni-koeln.de DESCRIPTION:Holger Gies\, Jena\n\nPhysics of the quantum vacuum\n\nModern physics describes matter and their interactions on the fundamental level a s quantum fields. Already their ground state - the quantum vacuum - exhibi ts properties analogous to complex media: fluctuations of quantum fields c an induce nonlocal and nonlinear phenomena.\nThis talk gives an overview o n present experiments using strong fields for probing the quantum vacuum. Illustrative theory methods will be discussed that help to understand quan tum fluctuations and quantum vacua intuitively. Recent ideas will be highl ighted that aim at searches for "New Physics" with strong fields.\n\nConta ct Person: Philipp Strack LOCATION:seminar room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Rafael Chaves DTSTART;TZID=Europe/Berlin:20150717T163000 DTEND;TZID=Europe/Berlin:20150717T180000 DTSTAMP:20260527T090436Z UID:0000000690@events.thp.uni-koeln.de DESCRIPTION:Rafael Chaves\, Institute for Theoretical Physics\, University of Cologne\n\nRevisiting Quantum Nonlocality from a Causal Inference Pers pective\n\nIt is a relatively new insight of classical statistics that emp irical data can contain information about causation rather than mere corre lation. Within that context\, during the past year we have developed and f ormalized a new research program for the study of causal relations in both the classical and quantum cases. In this presentation we will discuss two recent developments that highlight the\nvery fruitful interplay between t he causal inference literature and problems in quantum information\, a\nco nnection which is increasingly appreciated among quantum physicists. We wi ll describe a general algorithm for computing information-theoretic constr aints on the correlations that can arise from a given causal structure\, w here we allow for quantum systems as well as classical random variables. I n a second part\, we will revisit nonlocality from a causal inference pers pective and give an answer to the following question: How much do we need to relax the causal assumptions entering in Bell's theorem to\nclassically explain nonlocal correlations? \n\nContact Person: not specified LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Till Kranz DTSTART;TZID=Europe/Berlin:20150828T140000 DTEND;TZID=Europe/Berlin:20150828T153000 DTSTAMP:20260527T090436Z UID:0000000739@events.thp.uni-koeln.de DESCRIPTION:Till Kranz\, Oxford University\n\nBacteria and Trails on Surfa ces\n\nSwimming of Bacteria at low Reynolds numbers is relatively well und erstood.\nMuch less is known about bacteria crawling on surfaces. In parti cular as\nsome species leave sticky trails that are believed to help them coordinate.\nI will introduce a simple semi-microscopic model for the bact eria-trail\ninteraction. Based on this model I will discuss the effects of the\ntrail-mediated self-interaction on a single bacterium and whether or not it\nactually allows trail-following behaviour.\n\nContact Person: Joa chim Krug LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Alexander Drewitz DTSTART;TZID=Europe/Berlin:20151023T163000 DTEND;TZID=Europe/Berlin:20151023T173000 DTSTAMP:20260527T090436Z UID:0000000755@events.thp.uni-koeln.de DESCRIPTION:Alexander Drewitz\, Mathematisches Institut Köln\n\nThe maxim al particle of branching random walk in random environment\n\nOne-dimensio nal branching Brownian motion has been the subject of intensive research\, in particular during the last decade. We consider the discrete space vers ion of branching random walk and investigate the setting of a spatially ra ndom branching environment\; in particular we are interested in the positi on of the maximal particle. Via the Feynman-Kac formula this is connected to fluctuations of the solutions to the parabolic Anderson model (i.e.\, t he heat equation with a random potential) as well as to a randomized versi on of the Fisher-KPP equation. The Fisher-KPP equation is a fundamental re action-diffusion partial differential equation which had originally been i ntroduced in order to model the spread of an advantageous alelle in a popu lation of a one-dimensional habitat.\n\nContact Person: not specified LOCATION:seminar room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Pieter Rein ten Wolde DTSTART;TZID=Europe/Berlin:20151030T163000 DTEND;TZID=Europe/Berlin:20151030T180000 DTSTAMP:20260527T090436Z UID:0000000648@events.thp.uni-koeln.de DESCRIPTION:Pieter Rein ten Wolde\, AMOLF Amsterdam\n\nFundamental limits to chemical sensing\n\nCells can measure chemical concentrations with extr aordinary precision. This raises the question what is the fundamental limi t to the accuracy of chemical concentration\nmeasurements. In this talk\, I will show that the sensing accuracy of passive signaling systems is limi ted by the number of receptors\; a downstream processing network can never increase\nthe sensing precision beyond this limit. Non-equilibrium system s can beat this limit. However\, this requires receptors and their integra tion time\, downstream molecules\, and energy. Each\nresource imposes a fu ndamental sensing limit\, which means that the sensing precision is bounde d by the limiting resource and cannot be enhanced by increasing another re source. This\nresult yields a new design principle\, namely that of optima l resource allocation in cellular sensing. It states that in an optimally designed sensing system\, each resource is equally\nlimiting\, so that no resource is wasted. We find that the chemotaxis network of E. coli obeys t his principle\, indicating a selective pressure for the efficient design o f cellular sensing\nsystems.\n\n\nContact Person: Johannes Berg LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Matthias Christandl DTSTART;TZID=Europe/Berlin:20151106T163000 DTEND;TZID=Europe/Berlin:20151106T180000 DTSTAMP:20260527T090436Z UID:0000000698@events.thp.uni-koeln.de DESCRIPTION:Matthias Christandl\, University of Copenhagen\n\nFrom Pauli's Principle to Fermionic Entanglement\n\nThe Pauli exclusion principle is a constraint on the natural occupation numbers of fermionic states. It has been suspected for decades\, and only proved very recently\, that there is a multitude of further constraints on these numbers\, generalizing the Pa uli principle. Surprisingly\, these constraints are linear: they cut out a geometric object known as a polytope. This is a beautiful mathematical re sult\, but are there systems whose physics is governed by these constraint s? \n\nIn order to address this question\, we studied a system of a few fe rmions connected by springs. As we varied the spring constant\, the occupa tion numbers moved within the polytope. The path they traced hugs very clo se to the boundary of the polytope\, suggesting that the generalized const raints affect the system. I will mention the implications of these finding s for the structure of few-fermion ground states and then discuss the rela tion between the geometry of the polytope and different types of fermionic entanglement. \n\nContact Person: David Gross LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Eric Brunet DTSTART;TZID=Europe/Berlin:20151127T163000 DTEND;TZID=Europe/Berlin:20151127T180000 DTSTAMP:20260527T090436Z UID:0000000774@events.thp.uni-koeln.de DESCRIPTION:Eric Brunet\, ENS Paris\n\nUniversal vanishing corrections on the position of fronts in the Fisher-KPP class\n\nA moving interface\, or a front\, between a stable and an unstable medium is often described by an equation such as the Fisher-KPP (Kolmogorov-Petrovsky-Piscounov) equation . Such an equation appears in biology\, chemistry or theoretical physics. Thirty years ago\, Bramson gave rigorous sharp estimates on the position o f the front\, and\, fifteen years ago\, Ebert and van Saarloos heuristical ly identified universal vanishing corrections. In this seminar\, I will pr esent two new front equations which we believe to be in the same universal ity class as the Fisher-KPP equation. For the first equation\, we can writ e an exact relation between the initial condition and the positions of the front at all times. For the second equation\, probabilistic methods give very good estimates on the shape of the front at\nall times. In both cases \, we can recover and make precise the universal vanishing corrections on the position of the front.\n\n\n\nContact Person: Joachim Krug LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | David Gross DTSTART;TZID=Europe/Berlin:20151204T163000 DTEND;TZID=Europe/Berlin:20151204T180000 DTSTAMP:20260527T090436Z UID:0000000777@events.thp.uni-koeln.de DESCRIPTION:David Gross\, ITP Cologne\n\nFrom Single Pixel Cameras To Quan tum State Tomography\n\nEvery time the release button of a digital camera is pressed\, several megabytes of raw data are recorded. But the size of a typical jpeg output file is only 10% of that. What a waste! Can't we desi gn a process which records only the relevant 10% of the data to begin with ? I will give an introduction to the concepts and math of compressed sensi ng - a theory that achieves this trick for certain signals. A variant of c ompressed sensing aims to exploit representations of data in terms of low- rank matrices. There has been a fruitful exchange of ideas between this th eory and quantum physics. Methods that we had originally introduced in the context of quantum state estimation have since found applications to task s as diverse as face recognition\, the analysis of x-ray diffraction image s\, and the prediction of user preferences in online shops. Specific quant um information ideas that feature in this context including trace inequali ties and their use to prove large deviation bounds for random matrices\, p hase space methods\, and the notion of complex projective designs. \n\nCon tact Person: not specified LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Sebastian Diehl DTSTART;TZID=Europe/Berlin:20160108T163000 DTEND;TZID=Europe/Berlin:20160108T180000 DTSTAMP:20260527T090436Z UID:0000000787@events.thp.uni-koeln.de DESCRIPTION:Sebastian Diehl\, ITP Cologne\n\nUniversal Quantum Dynamics in Driven Open Many-Body Systems\, and Localized Majorana-like Modes in Inte racting Fermion Systems\n\nThe talk is divided into two parts.\nIn part on e\, we discuss universal aspects of quantum dynamics present in driven ope n many-particle systems. Oftentimes\, driven systems show full decoherence at large wavelength\, but we present two situations which do not follow t his generic pattern. The first concerns the critical dynamics in a driven open system with a dark state realizable in microcavity arrays\, and the o ther one an ensemble of Rydberg atoms\, in which coherent quantum dynamics leads to a variant of a non-equilibrium absorbing state transition withou t direct classical counterpart.\nIn part two\, we discuss\, in a number co nserving framework\, an exactly solvable model of interacting fermions sup porting non-local zero-energy Majorana-like edge excitations. The construc tion draws intuition from an approach of targeted dissipative cooling into topologically non-trivial states. The model has an exactly solvable line\ , on varying the density of fermions\, described by a topologically non-tr ivial ground state wave-function. We characterize its thermodynamic and to pological properties. Knowledge of the ground state wavefunction allows us to construct analytically number conserving braiding operators\, which ar e exponentially localized at the edges.\n\nContact Person: not specified LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Erik Aurell DTSTART;TZID=Europe/Berlin:20160115T163000 DTEND;TZID=Europe/Berlin:20160115T180000 DTSTAMP:20260527T090436Z UID:0000000748@events.thp.uni-koeln.de DESCRIPTION:Erik Aurell\, KTH Stockholm\n\nMinimal absent words in genome sequences\n\nAbsent words are sub-sequences of letters that cannot be foun d in a given text. Minimal absent words (MAWs) are absent words all of the sub-sequences of which can be found in the text.\nIt has been observed fo r some time that the length distribution of MAWs in genome sequences have a curious two-mode structure with on the one hand many long fairly short M AWs ("the\nbulk") and on the other hand some very long MAWs ("the tail"). I will show that the first feature arises from statistical sampling of sub -sequences from a random genome while the second\ncan be explained by a si mple probabilistic model of genome evolution. Tail MAWs also seem to carry biological information as will be discussed in the talk. We were led to t he study of\nMAWs from a biotechnological problem of optimal tag design fo r (tagged) RNA-sequencing. I will therefore also describe some of the resu lts obtained by this method to distinguish primary\nfrom processed RNA in the human pathogen Enterococcus faecalis\, including the discovery of many new non-coding genes in this organism.\n\nContact Person: Michael Lässig LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Tapio Ala-Nissilä DTSTART;TZID=Europe/Berlin:20160212T163000 DTEND;TZID=Europe/Berlin:20160212T180000 DTSTAMP:20260527T090436Z UID:0000000781@events.thp.uni-koeln.de DESCRIPTION:Tapio Ala-Nissilä\, Aalto University\, Helsinki\n\nDemon’s Work in the Classical and Quantum Worlds\n\nStochastic thermodynamics offe rs a powerful formalism to study\nfluctuating thermodynamic variables\, su ch as (free) energy\, entropy\,\nheat\, and work in small systems driven b eyond the linear response\nregime. Small electronic devices\, such as sing le-electron boxes and\nquantum dots have been recently shown to provide we ll-controlled\nbenchmarks for stochastic thermodynamics. In particular\, i t is\npossible to realize the ubiquitous concepts of a Szilard engine and\ na Maxwell’s demon in such systems. While stochastic\nthermodynamics giv es a complete theoretical picture for devices such\nas the Maxwell’s dem on at classical level\, attempts to generalize the\nconcept of work (and o ther thermodynamic quantities) to open\nquantum systems have met with some difficulties. The main problem\nin quantum mechanics is that there is no unique work operator\, since\nfor irreversible processes work depends both on the state of the\nsystem as well as the path taken.\n\nIn this talk I will discuss the analysis of devices such as the\nMaxwell’s demon based on stochastic thermodynamics at the classical\nlevel. I will then describe some recent progress in defining work\nand its moments for quantum system s within the two-measurement\nprotocol (TMP) approach\, which for isolated systems coincides with the\nclassical definition of work in the appropria te limit. In particular\, I will\nshow that using the TMP within the Linbl ad master equation formalism\nyields explicit results for driven\, open qu antum systems.\n\nContact Person: Joachim Krug LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Masaki Oshikawa DTSTART;TZID=Europe/Berlin:20160226T163000 DTEND;TZID=Europe/Berlin:20160226T173000 DTSTAMP:20260527T090436Z UID:0000000825@events.thp.uni-koeln.de DESCRIPTION:Masaki Oshikawa\, ISSP Tokyo\n\nSymmetry Protection of Quantum Phases\n\nClassification of quantum phases is one of the central problems in\nstatistical mechanics and condensed matter physics. Traditionally\,\n it had been associated to spontaneous symmetry breakings.\nHowever\, a ric h variety of quantum phases without any spontaneous\nsymmetry breaking hav e been found and dubbed as topological\nphases. Symmetries can still play an important role even when there\nis no spontaneous symmetry breaking\, a s some quantum phases\nare distinct only in the presence of certain symmet ries. I will review\nthe concept of "symmetry-protected topological phases " and then\ndiscuss our recent attempts in generalizing the notion of symm etry\nprotection of quantum phases.\n\nContact Person: Simon Trebst LOCATION:Seminar Room TP 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Roderich Moessner DTSTART;TZID=Europe/Berlin:20160408T140000 DTEND;TZID=Europe/Berlin:20160408T153000 DTSTAMP:20260527T090436Z UID:0000000828@events.thp.uni-koeln.de DESCRIPTION:Roderich Moessner\, MPI for Physics of Complex Systems\, Dresd en\n\nThermodynamics and order beyond equilibrium - the physics of periodi cally driven quantum systems\n\nThe field of thermodynamics is one of the crown jewels of classical\nphysics. Extending its ideas and concepts to th e non-equilibrium setting\nis a challenging topic of perennial interest. H ere\, we study perhaps the\nsimplest non-equilibrium class of quantum prob lems\, namely Floquet\nsystems\, i.e. systems whose Hamiltonians depend on time periodically\, \nH(t+T) = H(t). For these\, there is no energy conse rvation\, and hence not\neven a natural definition of temperature. We find that it is nonetheless\npossible to identify three fundamentally distinct thermodynamic ensembles.\nWe also ask if there exists a sharp notion of a phase in such driven\,\ninteracting quantum systems. Disorder turns out t o play a crucial role\,\nenabling the existence of states which are straig htforward analogues of\nequilibrium states with broken symmetries and topo logical order\, while\nothers - genuinely new to the Floquet problem - are characterized by a\ncombination of order and non-trivial periodic dynamic s.\n\nContact Person: Martin Zirnbauer LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Gunter M. Schütz DTSTART;TZID=Europe/Berlin:20160415T163000 DTEND;TZID=Europe/Berlin:20160415T180000 DTSTAMP:20260527T090436Z UID:0000000784@events.thp.uni-koeln.de DESCRIPTION:Gunter M. Schütz\, Forschungszentrum Jülich\n\nThe Fibonacci family of dynamical universality classes\n\nWe use the universal nonlinea r fluctuating hydrodynamics\napproach to study anomalous one-dimensional t ransport far from\nthermal equilibrium in terms of the dynamical structure function.\nGenerically for more than one conservation law mode coupling t heory\nis shown to predict a discrete family of dynamical universality\ncl asses with dynamical exponents which are consecutive ratios of\nneighborin g Fibonacci numbers\, starting with z = 2 (corresponding\nto a diffusive m ode) or z = 3/2 (Kardar-Parisi-Zhang (KPZ) mode).\nIf neither a diffusive nor a KPZ mode are present\, all Fibonacci\nmodes have as dynamical expone nt the golden mean z=(1+\\sqrt5)/2.\nThe scaling functions of the Fibonacc i modes are asymmetric Levy\ndistributions which are completely fixed by t he macroscopic\nstationary properties\, viz. the current-density relation and the\ncompressibility matrix of the system. The theoretical predictions \nare confirmed by Monte-Carlo simulations of a three-lane asymmetric\nsim ple exclusion process.\n\n\nContact Person: Joachim Krug LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Erwin Frey DTSTART;TZID=Europe/Berlin:20160513T163000 DTEND;TZID=Europe/Berlin:20160513T180000 DTSTAMP:20260527T090436Z UID:0000000824@events.thp.uni-koeln.de DESCRIPTION:Erwin Frey\, LMU München\n\nEvolutionary Games\n\nMicrobial l aboratory communities have become model systems for studying the complex interplay between nonlinear dynamics of evolutionary selection forces\, stochastic fluctuations arising\nfrom the probabilistic nature of intera ctions\, and spatial organization. Major research goals are to identify a nd understand mechanisms that ensures viability of microbial colonies by \nallowing for species diversity\, cooperative behavior and other kinds o f social behavior. A synthesis of evolutionary game theory\, nonlinear d ynamics\, and the theory of stochastic\nprocesses provides the conceptual framework for a deeper understanding of these ecological systems. In thi s talk\, we will give an introduction into the modern formulation of the se\ntheories and illustrate their effectiveness focusing on selected exa mples of microbial systems. We also discuss current challenges and future perspectives in quantifying\nbacterial population dynamics\, and how th is might have an impact on research in non-equilibrium physics.\n\nContac t Person: Joachim Krug LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Reinhard Werner DTSTART;TZID=Europe/Berlin:20160603T163000 DTEND;TZID=Europe/Berlin:20160603T180000 DTSTAMP:20260527T090436Z UID:0000000847@events.thp.uni-koeln.de DESCRIPTION:Reinhard Werner\, Leibniz-Universität\, Hannover\n\nMeasureme nt uncertainty relations\n\n\nThe textbook uncertainty relation due to Ken nard\, Weyl and Robertson is a "preparation uncertainty relation"\, which constrains how sharply the position and momentum distributions of a fixed state can be concentrated. It has nothing to say about error -disturbance tradeoffs for setups like Heisenberg's gamma-ray microscope from 1927. For mulated by Heisenberg only as a heuristic principle\, this tradeoff links the accuracy of an approximate position measurement to the possibility to retrieve the momentum after the measurement. We generalize this problem to a simpler one\, namely the quality of optimal joint measurements of pos ition and momentum. It is then only required that a device provides a posi tion value and a momentum value in each shot\, like the microscope and th e momentum retrieval in the error/disturbance case. We will show quantita tively that the distribution of the position outputs must in general diffe r from that of an ideal position measurement\, and similarly for momentum\ , where the respective deviations satisfy a relation looking formally like the textbook preparation uncertainty relation.\n\nOur setup is conceptual ly straightforward and covers arbitrary pairs or tuples of observables. It turns out that the equality of the preparation and measurement uncertaint y bounds is due to the high symmetry of canonical pairs of observables lin ked via Fourier transform. For generic pairs of observables the measuremen t uncertainty is larger than the preparation uncertainty.\n\nContact Perso n: David Gross LOCATION:Seminar room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Reinhard Meinel DTSTART;TZID=Europe/Berlin:20160610T163000 DTEND;TZID=Europe/Berlin:20160610T180000 DTSTAMP:20260527T090436Z UID:0000000814@events.thp.uni-koeln.de DESCRIPTION:Reinhard Meinel\, Friedrich-Schiller-Universität Jena\n\nCons tructive proof of the no-hair theorem\n\nAccording to the no-hair theorem\ , the Kerr-Newman black hole\nsolution represents the most general asympto tically flat\, stationary\n(electro-) vacuum black hole solution in genera l relativity. The talk\nshows how this solution can indeed be constructed as the unique solution\nto the corresponding boundary value problem of the axially symmetric\nEinstein-Maxwell equations in a straightforward manner .\n\nContact Person: Claus Kiefer LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Baruch Meerson DTSTART;TZID=Europe/Berlin:20160617T163000 DTEND;TZID=Europe/Berlin:20160617T180000 DTSTAMP:20260527T090436Z UID:0000000830@events.thp.uni-koeln.de DESCRIPTION:Baruch Meerson\, Hebrew University of Jerusalem\n\nWeak-noise theory and large deviations of surface height in the Kardar-Parisi-Zhang e quation\n\nThe Kardar-Parisi-Zhang (KPZ) equation describes an important u niversality class of nonequilibrium\nstochastic models\, including stochas tic interface growth. There has been much recent\ninterest in the one-poin t probability distribution P(H\, t) of height H of the evolving interface at\ntime t. I will show how one can use the weak-noise theory (also known as the optimal fluctuation\nmethod\, the macroscopic fluctuation theory\, or simply WKB) to evaluate P(H\, t) for different initial\nconditions. At small t and H\, P(H\,t) is Gaussian\, but its tails are non-Gaussian and h ighly asymmetric.\nIn a proper moving frame\, one of the tails agrees at a ll times with the asymptotics of the Tracy-Widom distribution (for the fla t and curved interface)\, and of the Baik-Rains distribution (for the stat ionary interface)\, previously observed at long times. The other tail disp lays a behavior that differs from the known long-time asymptotics. We argu e that this tail should be also observable at long times once |H| is very large. The case of stationary interface is especially interesting. Here at short times the large deviation function of the height exhibits a singula rity at a critical value of |H|.\n\nContact Person: Joachim Krug LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dieter Vollhardt DTSTART;TZID=Europe/Berlin:20160701T163000 DTEND;TZID=Europe/Berlin:20160701T180000 DTSTAMP:20260527T090436Z UID:0000000876@events.thp.uni-koeln.de DESCRIPTION:Dieter Vollhardt\, University of Augsburg\n\nSuperfluid Helium -3: Universal Concepts for Condensed Matter and the Big Bang\n\nSince thei r discovery in 1971 the superfluid phases of Helium-3 have\nproved to be t he ideal testing ground for many fundamental concepts of\nmodern physics. Phenomena such as anisotropic Cooper pairing\, p-wave states\,\nchirality\ , macroscopic quantum coherence\, spontaneous breaking of high\nsymmetries \, and exotic topological defects are not only an important\nenrichment of the physics of condensed matter\, but also provide important\nlinks to pa rticle physics\, defect formation in the early universe and\, most\nrecent ly\, quantum turbulence. I will present an introduction into the\nphysics of superfluid Helium-3 and describe the progress made in this\nfascinating field of basic research.\n\nContact Person: Philipp Strack LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Michael Spira DTSTART;TZID=Europe/Berlin:20160715T163000 DTEND;TZID=Europe/Berlin:20160715T180000 DTSTAMP:20260527T090436Z UID:0000000898@events.thp.uni-koeln.de DESCRIPTION:Michael Spira\, Paul Scherrer Institute\n\nHiggs Physics @ LHC \n\nThe recent discovery of the Higgs boson at the LHC marked the completi on of the theoretical description of strong\, weak and electromagnetic int eractions among the known elementary particles and builds up the basis of the Standard Model (SM) of particle physics. This talk will provide an int roduction into the physics of Higgs bosons and their quantitative tests at the LHC. This includes the decay and production profile of the SM Higgs b oson and will also make remarks about extensions of the SM and their Higgs bosons.\n\n\n\nContact Person: Alexander Altland LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | David Dean DTSTART;TZID=Europe/Berlin:20161021T163000 DTEND;TZID=Europe/Berlin:20161021T180000 DTSTAMP:20260527T090436Z UID:0000000900@events.thp.uni-koeln.de DESCRIPTION:David Dean\, University of Bordeaux\n\nStochastic Density Func tional Theory for Electrolytes Out of Equilibrium\n\nThe dynamics of inter acting Brownian particles can be described by a stochastic \nequation for the density field. I will show how the linearised version of this \nequa tion can be used to recover\, very simply\, certain of Onsager's results  \non electrolyte conductivity. In addition I will show how it can analyse the \nout of equilibrium thermal Casimir effect between parallel plates c ontaining \nBrownian charges\, in particular the case where the plates ar e held at different temperatures\nand when an electric field drives a curr ent in one of the plates.\n\n\nContact Person: Joachim Krug LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Daniel Loss DTSTART;TZID=Europe/Berlin:20161111T163000 DTEND;TZID=Europe/Berlin:20161111T180000 DTSTAMP:20260527T090436Z UID:0000000977@events.thp.uni-koeln.de DESCRIPTION:Daniel Loss\, University of Basel\n\nFrom Majorana Fermions to Parafermions in Nanowires and Atomic Chains\n\nI will present recent prog ress on Majorana fermions and other exotic excitations with non-Abelian br aid statistics that can emerge in condensed matter systems. These excitati ons have attracted wide attention recently\, also because of their potenti al applications in topological quantum computing. Majorana fermion zero-mo des and their generalizations\, parafermions\, can emerge in nanowires and atomic chains in the presence of spin orbit interaction or spatially peri odic magnetic fields\, in RKKY systems forming intrinsic spin helices\, in topological insulators\, and typically in the presence of superconductivi ty. I will discuss some candidate materials such as semiconducting Rashba nanowires and atomic magnetic chains and show some recent experimental pro gress. Finally\, I plan to discuss parafermions\, which\, in contrast to M ajorana fermions\, can emerge only in the presence of strong electron-elec tron interactions and have a more powerful braid statistics that enables e ntanglement and in particular exact CNOT gates by braiding alone (without the need of any measurements).\n\n\nContact Person: Alexander Altland LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Benedikt Sabaß DTSTART;TZID=Europe/Berlin:20161118T163000 DTEND;TZID=Europe/Berlin:20161118T180000 DTSTAMP:20260527T090436Z UID:0000000945@events.thp.uni-koeln.de DESCRIPTION:Benedikt Sabaß\, FZ Jülich\n\nMicromechanics of Life: Coordi nation of Forces by Eukaryotes and Prokaryotes\n\nCells have the ability t o generate mechanical forces. Coordination of these forces is not only imp ortant for multicellular life\, but also plays a role for various diseases . We combine physical theory and traction microscopy to uncover mechanisms of how cells feel and respond to forces. Here\, we present a synopsis of recent findings on mechanisms of collective organization\, ranging from ba cteria to eukaryotic tissue cells.\n\n\nContact Person: not specified LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Walter Hofstetter DTSTART;TZID=Europe/Berlin:20161125T163000 DTEND;TZID=Europe/Berlin:20161125T180000 DTSTAMP:20260527T090436Z UID:0000000888@events.thp.uni-koeln.de DESCRIPTION:Walter Hofstetter\, Johann Wolfgang Goethe-Universität Frankf urt\n\nInteracting topological states of ultracold lattice gases\n\nThe l ast years have witnessed dramatic progress in experimental control and the oretical modeling of quantum simulations based on ultracold atoms. Major r ecent developments include synthetic gauge fields for neutral atoms\, whic h allow the simulation of topologically nontrivial phases of matter with s trong interactions. I will discuss two examples: \n\nWe consider a spinfu l and time-reversal invariant version of the Hofstadter-Harper problem\, w hich has been realized in ultracold atoms\, with an additional staggered p otential and spin-orbit coupling. Without interactions\, the system exhibi ts various phases such as topological and normal insulator\, metal and sem i-metal phases with two or even more Dirac cones. Using real-space dynamic al mean-field theory (DMFT)\, we investigate the stability of the Quantum Spin Hall state in the presence of strong interactions. To test the bulk-b oundary correspondence between edge mode parity and bulk Chern index of th e interacting system\, we calculate an effective topological Hamiltonian b ased on the local self-energy of DMFT. \n\nWe furthermore investigate the Haldane honeycomb lattice tight-binding model\, for bosons with additiona l local Hubbard interactions. We analyze the ground state phase diagram at filling one\, and uncover three distinct phases: a uniform superfluid (SF )\, a chiral superfluid (CSF) and a plaquette Mott insulator with local cu rrent loops (PMI). \n\nContact Person: Sebastian Diehl LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Johannes Berg DTSTART;TZID=Europe/Berlin:20161216T163000 DTEND;TZID=Europe/Berlin:20161216T180000 DTSTAMP:20260527T090436Z UID:0000000986@events.thp.uni-koeln.de DESCRIPTION:Johannes Berg\, University of Cologne\, Institute for Theoreti cal Physics\n\nStatistical physics of the inverse Ising problem\n\nThe inv erse Ising problem seeks to reconstruct the parameters of an Ising Hamilto nian on the basis of spin configurations sampled from the Boltzmann measur e. The last decade has witnessed many applications of the inverse Ising pr oblem driven by the advent of large-scale data in different scientific dis ciplines\, especially biology. In this talk I will give an introduction t o the inverse Ising problem\, discussing its applications as well as diffe rent approaches from statistical physics. A particular focus is on the lin k between approaches to the inverse Ising problem based on the optimisatio n of some `objective function' and the statistical physics of disordered s ystems. This allows to characterise the performance of an arbitrary object ive function and to calculate the objective function which optimally recon structs the model parameters.\n\n\nContact Person: not specified LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Malte Henkel DTSTART;TZID=Europe/Berlin:20170113T163000 DTEND;TZID=Europe/Berlin:20170113T180000 DTSTAMP:20260527T090436Z UID:0000000966@events.thp.uni-koeln.de DESCRIPTION:Malte Henkel\, Universite de Lorraine Nancy\n\nNew dynamical s ymmetries in interface growth: what do we know about them and what do they teach us ?\n\nInterface growth is a paradigmatic example of a complex sys tem made from a large number of strongly interacting degrees of freedom\, with dynamically created long-range correlations. Such systems can undergo physical ageing\, that is they display (i) slow relaxational behaviour\, (ii) breaking of time-translation-invariance and (iii) dynamical scaling. Through simulations and simple exactly solvable models\, we investigate in to the existence of new\, non-trivial dynamical symmetries extending dynam ical scaling and their possible consequences.\n\nContact Person: Joachim K rug LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | William G. Unruh DTSTART;TZID=Europe/Berlin:20170120T163000 DTEND;TZID=Europe/Berlin:20170120T180000 DTSTAMP:20260527T090436Z UID:0000000946@events.thp.uni-koeln.de DESCRIPTION:William G. Unruh\, University of British Columbia\, Vancouver\ n\nMeasuring Black Hole radiation in the lab\n\nHawking's prediction that black holes should radiate was one of the biggest surprizes in physics of the late 20th century. It has dominated much of the study in the interface between gravity and Quantum Mechanics ever since. The calculation Hawking presented is problematic\, and thus experimental confirmation would be go od. Unfortunately\, finding small black holes is hard. However\, there tur n out to be analog systems\, systems with horizons which one can and is st udying in the lab. I will present the arguments and the current experiment al effort to see the radiation\, and the arguments that some experiments h ave already seen it.\n\nContact Person: Claus Kiefer LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Klaus Richter DTSTART;TZID=Europe/Berlin:20170127T163000 DTEND;TZID=Europe/Berlin:20170127T180000 DTSTAMP:20260527T090436Z UID:0000000991@events.thp.uni-koeln.de DESCRIPTION:Klaus Richter\, University of Regensburg\n\nSemiclassical Path s to Many-Body Interference\n\nConcepts based on multi-particle interferen ce have been proven very fruitful for better understanding\nvarious differ ent many-body phenomena\, including quantum dynamics of cold atoms\, "many -body localization"\,\ncorrelated transport through molecules\, or scatter ing in photonic networks. We will consider such phenomena\nusing semiclass ical techniques based on interfering Feynman paths.\nA major objective of such approaches to an interacting many-body system is to combine\ninformat ion of its two complementary classical limits\, namely a classical system of particles\nand/or a classical field theory\, into a unified framework\, providing a picture of many-body interference\nbased on coherent sums ove r classical solutions.\nFollowing this direction we will illustrate recent progress in the semiclassical analysis of many-body\ninterference using a prime example of integrable quantum field theory\, the Lieb-Liniger model \, describing\ninteracting bosons on a ring. We show that\, in the limit o f high excitations\, its spectrum can be\nunderstood by means of suitable generalizations of the so-called Weyl expansion for the smooth part\, and a\ntrace formula for the oscillatory part\, revealing a spectral shell str ucture in terms of many-body periodic\norbits.\nWe will then show how for large particle number the complementary classical limit of the Lieb-Linige r model\,\ngiven by a nonlinear Schroedinger equation\, admits as well an analysis as an integrable classical system\,\nnow near its ground state. T his enables the description of a sequence of quantum phase transitions ari sing\nfor increasing (attractive) interaction\, along with an understandin g of numerical results for the spreading\nof information around criticalli ty.\nIn the opposite case of non-integrable systems\, applications of many particle interference comprise\ncoherent backscattering and echo phenomen a in Fock space. \n\nContact Person: Alexander Altland LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Sebastian Huber DTSTART;TZID=Europe/Berlin:20170203T163000 DTEND;TZID=Europe/Berlin:20170203T173000 DTSTAMP:20260527T090436Z UID:0000000936@events.thp.uni-koeln.de DESCRIPTION:Sebastian Huber\, ETH Zurich\n\nTopological Mechanical Metamat erials\n\nThe elastic properties of materials are determined by a few mate rial constants such as the Young’s modulus. Using super-structures one c an effectively change these “constants”. In this way we obtain functio nalities such as wave-guiding\, acoustic lensing or programmable failure. I will show how topological band theory\, known from the description of el ectrons in solids\, provides us with a powerful design-principle for such mechanical metamaterials.\n\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Hanno Schmiedt DTSTART;TZID=Europe/Berlin:20170512T163000 DTEND;TZID=Europe/Berlin:20170512T180000 DTSTAMP:20260527T090436Z UID:0000001038@events.thp.uni-koeln.de DESCRIPTION:Hanno Schmiedt\, University of Cologne\n\nSymmetry and dynamic s in floppy molecules: A new five-dimensional super-rotor model and its co nsequences\n\nExtremely floppy molecules are indescribable by the common i deas of molecular physics. Their ground state wave functions are highly de localized and the concept of molecular structure breaks down. Recently\, w e established a fundamentally new 'super-rotor' model\, which is based on a five-dimensional rotational symmetry. The respective states are describe d by the irreducible representations of SO(5) and the Hamiltonian is propo rtional to the respective Casimir operator. The prototypical example of fl oppy molecules is protonated methane\, which was measured only recently in the Cologne lab. With our simple model\, we are - for the first time - ab le to predict energy levels which actually compare very favourably to the experimental values. In addition\, the exchange symmetry of the protons ca n be\ndetermined by using an isomorphism of the permutation group to a sub group of SO(5). In this talk\, we discuss the basic concepts of this new a pproach and ask some of the most urgent questions for\nfurther development s.\n\nContact Person: Alexander Altland LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Muhittin Mungan DTSTART;TZID=Europe/Berlin:20170519T163000 DTEND;TZID=Europe/Berlin:20170519T180000 DTSTAMP:20260527T090436Z UID:0000001079@events.thp.uni-koeln.de DESCRIPTION:Muhittin Mungan\, Bogazici University and Bonn University\n\nD epinning as a Coagulation Process\n\nWe consider a one-dimensional model t hat describes the depinning of an\nelastic chain of particles in a strongl y pinning\, phase-disordered periodic\nenvironment under a slowly increasi ng driving force. The evolution towards\ndepinning occurs by the triggerin g of avalanches in regions of activity\nwhich are at first isolated\, but later grow and merge. For large system\nsizes the dynamically critical beh avior is dominated by the coagulation of\nthese active regions. Our analys is and numerical simulations show that the\nevolution of the sizes of acti ve regions is well described by a Smoluchowski\ncoagulation equation\, all owing us to predict correlation lengths and\navalanche sizes in terms of c ertain moments of the size distribution. Time\npermitting\, we will also b riefly present work in progress on the thermal\nbehaviour of the model.\n\ n\nContact Person: Joachim Krug LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Edgar Roldan DTSTART;TZID=Europe/Berlin:20170526T163000 DTEND;TZID=Europe/Berlin:20170526T180000 DTSTAMP:20260527T090436Z UID:0000001078@events.thp.uni-koeln.de DESCRIPTION:Edgar Roldan\, MPI-PKS Dresden\n\nMartingale theory for nonequ ilibrium thermodynamics\n\nThe laws of thermodynamics can be extended to m esoscopic systems for which energy changes are on the order of the thermal energy are relevant. Therefore\, thermodynamic observables associated wit h mesoscopic degrees of freedom are stochastic. A key example of such ther modynamic observable is the stochastic entropy production in nonequilibriu m processes. Little is known beyond fluctuation theorems about universal s tatistics of entropy-production fluctuations. Using Martingale theory we h ave discovered novel universal statistics of stochastic entropy production in nonequilibrium steady states such as: (i) The distribution of the nega tive record (which we call infimum) of entropy production (ii) the passage probabilities of entropy production\; (iii) the stopping-time fluctuation s of entropy production. Our work is based on the finding that in a nonequ ilibrium steady state\, the exponential of minus the entropy production is a martingale process. A martingale is a process representing a fair game with no net gain or loss and its connection to thermodynamics has not been fully explored yet. Notably\, our results have interesting implications f or stochastic processes that can be discussed in colloidal systems and act ive molecular processes. For example\, we make predictions for the distrib ution of the maximum backtrack depth of RNA polymerases during transcripti on.\n\nContact Person: Joachim Krug LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Tommaso Calarco DTSTART;TZID=Europe/Berlin:20170602T163000 DTEND;TZID=Europe/Berlin:20170602T180000 DTSTAMP:20260527T090436Z UID:0000001072@events.thp.uni-koeln.de DESCRIPTION:Tommaso Calarco\, Ulm University\n\nQuantum technologies and q uantum control\n\nThe control of quantum states is essential both for fund amental investigations and for technological applications of quantum physi cs. In quantum few-body systems\, decoherence arising from interaction wit h the environment hinders the realization of desired processes. In quantum many-body systems\, complexity of their dynamics further makes state prep aration via external manipulation highly non-trivial. An effective strateg y to counter these effects is offered by quantum optimal control theory\, exploiting quantum coherence to dynamically reach a desired goal with high accuracy even under limitations on resources such as time\, bandwidth\, a nd precision. In this talk I will (i) introduce the quantum optimal contro l method we developed to this aim\, the CRAB (Chopped Random Basis) algori thm\, (ii) present experimental results obtained via its application to va rious physical systems\, from quantum logical operations in solid-state qu antum optics to quantum criticality in ultra-cold atoms\, (iii) use these examples to illustrate the quantum speed limit\, i.e. the maximum speed ac hievable for a given quantum transformation\, and (iv) propose a way to ch aracterise the latter in an information-theoretical fashion by the bandwid th of the optimized control pulses. \n\nContact Person: Achim Rosch LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | David Mross DTSTART;TZID=Europe/Berlin:20170623T163000 DTEND;TZID=Europe/Berlin:20170623T173000 DTSTAMP:20260527T090436Z UID:0000001024@events.thp.uni-koeln.de DESCRIPTION:David Mross\, Weizmann Institute of Science\n\nThe power of vo rtices – dual perspectives on exotic quantum phases\n\nThe analysis of t opological excitations in interacting many-body systems often provides imp ortant insights into quantum phases and phase transitions. Seminal example s are the (thermal) BKT transition as well as the (quantum) superfluid-Mot t insulator transition\, which are naturally described in terms of vortice s. More recently\, such a ‘dual’ formulation has proven extremely illu minating in the study of exotic phases of matter that host fractional exci tations\, e.g.\, in topological phases and quantum magnets. In my talk\, I will review the dual description of conventional phases of matter and exp lain how exotic\, fractionalized phases are captured within this approach. I will then generalize these dualities to fermionic systems\, and discuss the implications for the half-filled Landau level and strongly interactin g surfaces of topological insulators. Finally\, I will describe how two-di mensional Dirac fermions (and their symmetries) can be mapped onto interac ting bosons.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Roman Riwar DTSTART;TZID=Europe/Berlin:20170627T160000 DTEND;TZID=Europe/Berlin:20170627T170000 DTSTAMP:20260527T090436Z UID:0000001106@events.thp.uni-koeln.de DESCRIPTION:Roman Riwar\, Institute for Theoretical Nanoelectronics\, FZ J ülich\n\nTopological electric circuits\n\nThe prospect of intrinsically p rotected quantum computing is driving the research on topological quantum systems. Materials with a topologically nontrivial band structure are howe ver difficult to manufacture experimentally. We recently showed that topol ogical materials can be engineered by quite simple means\, when considerin g a different space: superconducting junctions have the phase difference a nd the number of transported charges across the junction as conjugate vari ables. In the main part of the talk\, I will present the example of a four -terminal junction whose energy spectrum exhibits Weyl singularities in th e space of three independent phases\, which thus play the role of\nquasimo menta. The nonzero Chern number can be directly probed through a transport measurement\, namely\, through a quantised transconductance. In the final part of the talk\, I will provide an outlook on future directions. For on e\, electric circuits may be used to study topological phase transitions s pecific to open systems out of equilibrium\, and secondly\, they may exhib it a so far unexplored connection between topology and quantum thermodynam ics.\n\nContact Person: Achim Rosch LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Andreas Winter DTSTART;TZID=Europe/Berlin:20170630T163000 DTEND;TZID=Europe/Berlin:20170630T173000 DTSTAMP:20260527T090436Z UID:0000001028@events.thp.uni-koeln.de DESCRIPTION:Andreas Winter\, Universitat Autònoma de Barcelona\n\nGrand c anonical Gibbs state for systems with non-commuting charges\n\nThe grand c anonical ensemble lies at the core of quantum and classical  \nstatistica l mechanics. A small system thermalizes to this ensemble while\nexchanging heat and particles with a bath. A quantum system may exchange \nquantiti es represented by operators that fail to commute. Whether such \na ​ ​ system thermalizes and what form the thermal state has are questions  \nabout ​ ​ truly quantum thermodynamics. Here we investigate this the rmal \nstate from ​ ​ three perspectives. First\, we introduce an app roximate\nmicrocanonical ensemble. If this ensemble characterizes the syst em-\nand-bath composite\, tracing out the bath yields the system's thermal  \nstate. This state is expected to be the equilibrium point\, we argue\,  \nof typical dynamics. Finally\, we define a resource-theory model for\n thermodynamic exchanges of noncommuting observables. Complete passivity\n ​-- ​ the inability to extract work from equilibrium states ​ ​ -- ​\, ​ implies \nthe thermal state's form\, too. Our work opens new a venues into \nequilibrium in the presence of quantum noncommutation. ​ \n[Based on arXiv:1512.01189]​ \n\n\n\nContact Person: David Gross LOCATION:SR 0.03 TP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Nicolas Regnault DTSTART;TZID=Europe/Berlin:20170707T163000 DTEND;TZID=Europe/Berlin:20170707T180000 DTSTAMP:20260527T090436Z UID:0000001103@events.thp.uni-koeln.de DESCRIPTION:Nicolas Regnault\, ENS Paris\n\nMany body localization and the rmalization: (machine) learning from the entanglement spectrum\n\nWe numer ically explore the many body localization transition through the lens of t he entanglement spectrum\, i.e. the spectrum of the reduced density matrix . The level statistics of the entanglement spectrum as obtained through nu merical diagonalization\, unveil structures beyond that revealed by more l imited measures such as entanglement entropy. We will also show that a sim ple artificial neural network trained on entanglement spectra of individua l states of a many-body quantum system can be used to determine the transi tion between a many-body localized and a thermalizing regime.\n\nContact P erson: Maria Hermanns LOCATION:0.03 ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Andrei Bernevig DTSTART;TZID=Europe/Berlin:20170714T163000 DTEND;TZID=Europe/Berlin:20170714T173000 DTSTAMP:20260527T090436Z UID:0000001076@events.thp.uni-koeln.de DESCRIPTION:Andrei Bernevig\, Princeton University\n\nHow to find topologi cal states of matter\n\nThe previous 11 years have seen several breakthrou ghs in our understanding of topological states of matter. New Insulators a nd semimetals\, exhibiting new properties imposed by a variety of symmetr ies (the most well known of which is time reversal) have been theoreticall y predicted and experimentally discovered. These materials are described b y topological indices\, a set of "serial numbers" that characterize the st ate of matter. \n\nIn this talk\, I will review the progress made in these years with a focus on the prediction of new topological indices and on ma terial discovery. I will then show a surprising link between chemistry bon ding and topological states of matter which leads to the prediction of man y new classes of materials as topological. \n\nContact Person: Simon Trebs t LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Till Kranz DTSTART;TZID=Europe/Berlin:20171020T163000 DTEND;TZID=Europe/Berlin:20171020T180000 DTSTAMP:20260527T090436Z UID:0000001156@events.thp.uni-koeln.de DESCRIPTION:Till Kranz\, ITP & DLR\n\nRheology of Granular Fluids: An Inte gration Through Transients Approach\n\nFlows of large numbers of macroscop ic particles (sand grains\, cereals\, ball bearings\, etc.) occur in natur al phenomena like land slides or avalanches and are an important part of m any industrial processes.\nThe flow behavior of granular fluids displays a rich rheology including Newtonian\, shear thinning\, and shear thickening regimes as well as the famous Bagnold scaling. The non-equilibrium nature of granular\nflows and the high densities and shear rates involved make a theoretical description challenging. I will begin with a qualitative disc ussion of what determines the flow behavior. Based on this discussion I\nw ill develop a theory from first principles that makes it quantitative and allows the prediction of flow curves and transport coefficients.\n\n\nCont act Person: not specified LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Zi Yang Meng DTSTART;TZID=Europe/Berlin:20171110T163000 DTEND;TZID=Europe/Berlin:20171110T173000 DTSTAMP:20260527T090436Z UID:0000001122@events.thp.uni-koeln.de DESCRIPTION:Zi Yang Meng\, Institute of Physics\, Chinese Academy of Scien ces\n\nItinerant quantum criticality\, self-learning Monte Carlo\, duality and all that\n\nBased on the recent conceptual and technical developments of quantum Monte Carlo simulations in correlated electron systems\, I wil l present and discuss fresh results of itinerant quantum\ncritical points\ , i.e.\, the critical phenomena arising from the strong coupling between F ermi surface and bosonic fluctuations\, which are made possible by the sel f-learning Monte Carlo scheme. After\nwhich\, I will also discuss the late ly proposed duality relations between interaction-driven topological phase transitions and deconfined quantum critical points\, which is verified vi a unbiased\nlarge-scale quantum Monte Carlo simulations.\n\n\nContact Pers on: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | John Bechhoefer DTSTART;TZID=Europe/Berlin:20171117T163000 DTEND;TZID=Europe/Berlin:20171117T180000 DTSTAMP:20260527T090436Z UID:0000001149@events.thp.uni-koeln.de DESCRIPTION:John Bechhoefer\, Simon Fraser University\, Vancouver\n\nThe d etails are in the devil: Experiments on Maxwell's demon and the role of in formation in thermodynamics\n\nOne hundred and fifty years ago\, Maxwell's demon was first posed as a fundamental challenge to the newly developed f ield of statistical physics. Just two months later\, Maxwell's paper "On g overnors" gave the first analysis of a feedback system. These two foundati onal works reflect the fundamental and practical aspects of control. Here\ , I will present an experiment that unites the two: using feedback to crea te `impossible' dynamics\, we make a Maxwell demon that can reach the fund amental limits to control set by thermodynamics. We test - and then extend - Rolf Landauer's 1961 prediction that information erasure requires at le ast as much work as can be extracted from a system by virtue of informatio n. These fundamental thermodynamic limits are benchmarks for evaluating th e performance of practical information engines\, such as those active with in cells and other complex systems.\n\nContact Person: Joachim Krug LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Peter Mörters DTSTART;TZID=Europe/Berlin:20171124T163000 DTEND;TZID=Europe/Berlin:20171124T180000 DTSTAMP:20260527T090436Z UID:0000001157@events.thp.uni-koeln.de DESCRIPTION:Peter Mörters\, Mathematical Institute\, Cologne\n\nMetastabi lity of the contact process on evolving scale-free networks\n\nWe study th e contact process in the regime of small infection rates on scale-free net works evolving by stationary dynamics. A parameter allows us to interpolat e between slow (static) and fast (mean-field) network dynamics. For two pa radigmatic classes of networks we investigate transitions between phases\n of fast and slow extinction and in the latter case we analyse the density of infected vertices in the metastable state. This is joint work with Emma nuel Jacob (ENS Lyon) and Amitai Linker (Universidad de Chile).\n\n\nConta ct Person: Joachim Krug LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Rainer Klages DTSTART;TZID=Europe/Berlin:20171201T163000 DTEND;TZID=Europe/Berlin:20171201T180000 DTSTAMP:20260527T090436Z UID:0000001167@events.thp.uni-koeln.de DESCRIPTION:Rainer Klages\, Queen Mary University London\n\nStatistical Ph ysics and Anomalous Dynamics of Foraging\n\nA question that attracted a lo t of attention in the past two decades is whether biologically relevant se arch strategies can be identified by statistical data analysis and mathema tical modeling. A\nfamous paradigm in this field is the Levy Flight Foragi ng Hypothesis. It states that under certain mathematical conditions Levy d ynamics\, which defines a key concept in the theory of anomalous stochasti c processes\, leads to an optimal search strategy for foraging organisms. This hypothesis is discussed very controversially in the current literatur e. I will review examples and counterexamples of experimental data and the ir analyses confirming and refuting it. Related to this debate is own work about\nbiophysical modeling of bumblebee flights under predation thread a nd biological cell migration\, both based on experimental data analysis\, which I briefly outline.\n\nContact Person: Joachim Krug LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Michael Klatt DTSTART;TZID=Europe/Berlin:20180112T163000 DTEND;TZID=Europe/Berlin:20180112T173000 DTSTAMP:20260527T090436Z UID:0000001170@events.thp.uni-koeln.de DESCRIPTION:Michael Klatt\, Karlsruhe Institute of Technology\n\nUniversal hidden order in amorphous cellular geometries\n\nStarting from an amorpho us partitioning of space into cells\, we iteratively optimize the `central ity' of the\ncells\, minimizing the so-called Quantizer energy. The energy landscape is replete with local minima to which the system converges desp ite the existence of lower-energy crystalline configurations. Irrespective of the level and type of disorder in the initial configurations\, the tes sellations converge to the same amorphous state\, as measured by the same structure factor and energy distributions. The final disordered configurat ions exhibit an anomalous suppression of long-wavelength density fluctuati ons\, known as hyperuniformity. For systems related to the Quantizer probl em\, such as selfassembled copolymeric phases\, our findings suggest the p ossibility of stable disordered hyperuniform phases.\n\nContact Person: Ma tthias Sperl LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Jürgen Berges DTSTART;TZID=Europe/Berlin:20180119T163000 DTEND;TZID=Europe/Berlin:20180119T180000 DTSTAMP:20260527T090436Z UID:0000001164@events.thp.uni-koeln.de DESCRIPTION:Jürgen Berges\, University of Heidelberg\n\nUniversality far from equilibrium: From the early universe to ultracold quantum gases\n\nIn recent years there have been important advances in understanding isolated quantum systems far from equilibrium. Prominent examples include the (pre -)heating process in the early universe after inflation\, the initial sta ges in collisions of relativistic nuclei at giant laboratory facilities\, as well as table-top experiments with ultracold quantum gases. Even though the typical energy scales of these systems vastly differ\, they can show very similar dynamical properties. Certain characteristic numbers can eve n be quantitatively the same\, defining nonthermal universality classes. O ne may use this universality to learn from experiments with cold atoms asp ects about the dynamics during the early stages of our universe.\n\nContac t Person: Alexander Altland LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Paul Busch DTSTART;TZID=Europe/Berlin:20180202T163000 DTEND;TZID=Europe/Berlin:20180202T173000 DTSTAMP:20260527T090436Z UID:0000001191@events.thp.uni-koeln.de DESCRIPTION:Paul Busch\, University of York\n\nMeasurement uncertainty rel ations for qubits: theory and experiment\n\nIn standard formulations of th e uncertainty principle\, two fundamental features are typically cast as i mpossibility statements: two noncommuting observables cannot in general bo th be sharply defined (for\nthe same state)\, nor can they be measured joi ntly. The pioneers of quantum mechanics were acutely aware and puzzled by this fact\, and it motivated Heisenberg to seek a mitigation\, which he fo rmulated in his seminal paper of 1927. He provided intuitive arguments to show that the values of\, say\, the position and momentum of a particle ca n at least be unsharply defined\, and they can be measured together provid ed some approximation errors are allowed. Only now\, nine decades later\, a working theory of approximate joint measurements is taking shape\, leadi ng to rigorous and experimentally testable formulations of associated erro r tradeoff relations. Here we briefly review this new development\, explai ning the concepts and steps taken in the construction of optimal joint app roximations of pairs of incompatible observables. As a case study\, we ded uce measurement uncertainty relations for qubit observables using two dist inct error measures. We provide an operational\ninterpretation of the erro r bounds and discuss some of the first experimental tests of such relation s.\nThe talk is based on the review paper arXiv:1512.00104v3.\n\nContact P erson: David Gross LOCATION:SR 0.03 TP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Matteo Rizzi DTSTART;TZID=Europe/Berlin:20180420T163000 DTEND;TZID=Europe/Berlin:20180420T173000 DTSTAMP:20260527T090436Z UID:0000001248@events.thp.uni-koeln.de DESCRIPTION:Matteo Rizzi\, University of Mainz\n\nExploring Synthetic Quan tum Matter with Tensor Networks\n\nThe quest for understanding and exploit ing many-body phenomena has received new spur in the last decades by the i ncreasing capacity of harnessing quantum particles to tailor more and more sophisticated systems. Among others\, cold atomic gases are one of the mo st flexible platforms for realising such “Synthetic Quantum Matter”. H ere\, I focus on the interplay of geometrical constraints\, tunable intera ctions of various range and (artificial) gauge fields to access i) interac ting topological states of matter and ii) many-body effects in the transpo rt properties of low-dimensional systems. In order to broaden our understa nding\, besides mappings onto effective models\, I exploit quantum-informa tion-inspired numerical techniques\, namely Tensor Networks algorithms. In this way\, insights about the entanglement structure of correlated states are also gained.\nIn this talk\, I will provide an overview of some of my recent results: in particular\, I will concentrate on the Creutz-Hubbard ladder\, a neat playground to address the above challenges\, including the generation of flat bands as well as of non-doubled Dirac dispersion relat ions. In [1]\, I will present a theoretical analysis of the competition be tween correlated topological phases and orbital quantum magnetism\, and th e prediction of topological quantum phase transitions with different under lying conformal field theories (CFTs). In [2]\, I will examine the respons e of an interacting system of Dirac-Weyl fermions confined in a one-dimens ional (1D) ring: i will show that the tuning of repulsive interactions lea ds to a unique many-body system that displays an enhancement of the Drude weight—the zero-frequency peak in the ac conductivity—with respect to the non-interacting value. Finally\, I will review our proposal to experim entally realize this model in a synthetic ladder\, made of two internal st ates of ultracold fermionic atoms in a one-dimensional optical lattice.\n\ nReferences:\n[1] J. Jünemann\, et al.\, PRX 7\, 031057 (2017)\n[2] M. Bi schoff\, et al.\, PRB 96\, 241112(R) (2017)\n\nContact Person: David Gross LOCATION:SR 0.03 TP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | T. P. Singh DTSTART;TZID=Europe/Berlin:20180427T163000 DTEND;TZID=Europe/Berlin:20180427T173000 DTSTAMP:20260527T090436Z UID:0000001195@events.thp.uni-koeln.de DESCRIPTION:T. P. Singh\, Tata Institute\, Mumbai\n\nIs quantum theory exa ct\, or approximate?\n\nWhy does the wave-function of a quantum system col lapse during a measurement? It maybe possible to answer this question\, as in the many-worlds interpretation\, without modifying the theory. In this case\, quantum theory is exact. On the other hand\, it maybe that the the ory has to be modified\, as in\nthe phenomenological model of Spontaneous Collapse. This model proposes that every quantum particle in nature underg oes spontaneous collapse\, and that collapse is a fundamental property of nature\, along with Schrödinger evolution. The predictions of this model differ from those of quantum theory\, and we review the current experiment al bounds on these models. We also review work which attempts to provide a theoretical underpinning for this phenomenological model\, including the possible role of gravity\, and a possible inter-connection between the mea surement problem and the problem of time in quantum theory.\n\nContact Per son: Claus Kiefer LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Adrian Del Maestro DTSTART;TZID=Europe/Berlin:20180518T163000 DTEND;TZID=Europe/Berlin:20180518T173000 DTSTAMP:20260527T090436Z UID:0000001229@events.thp.uni-koeln.de DESCRIPTION:Adrian Del Maestro\, University of Vermont\n\nEntanglement are a law in superfluid 4He\n\nArea laws were first discovered by Bekenstein a nd Hawking\, who found that the entropy of a black hole grows proportional to its surface area\, and not its volume. Entropy area laws have since b ecome a fundamental part of modern physics\, from the holographic principl e in quantum gravity to ground state wavefunctions of quantum matter\, whe re entanglement entropy is generically found to obey area law scaling. As no experiments are currently capable of directly probing the entanglement area law in naturally occurring many-body systems\, evidence of its existe nce is based on studies of simplified theories. Using new exact microscopi c path integral ground state Monte Carlo simulations of superfluid 4He\, w e demonstrate for the first time area law scaling of entanglement entropy in a real quantum liquid in three dimensions. We validate the fundamental principles underlying its physical origin\, and present an "entanglement e quation of state" showing how it depends on the density of the superfluid. \n\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Jan M. Pawlowski DTSTART;TZID=Europe/Berlin:20180608T163000 DTEND;TZID=Europe/Berlin:20180608T173000 DTSTAMP:20260527T090436Z UID:0000001249@events.thp.uni-koeln.de DESCRIPTION:Jan M. Pawlowski\, University of Heidelberg\n\nStrongly correl ated QCD: from chiral symmetry breaking & confinement to the dynamics of h eavy-ion collisions\n\nThe theory of strong interactions\, QuantumChromoDy namics\, exhibits a\nstrongly correlated low energy regime. This regime is governed by two\nphenomena\, strong spontaneous chiral symmetry breaking and confinement.\nWhile the former phenomenon is responsible for most of t he visible mass\nin the universe\, the emergence of the latter is still no t fully understood.\n\nExperimental access to QCD at large and small energ ies\, temperatures and\ndensities is obtained via heavy ion collisions wit hin a non-equilibrium evolution.\nIn summary the understanding of QCD requ ires theoretical approaches that can\ndeal with both\, strongly-correlated physics as well as non-equilibrium processes.\n\nThe past years have seen tremendous progress in the description of QCD at vanishing\nand finite te mperature and density with functional diagrammatic approaches\, such as\nt he functional renormalisation group or Dyson-Schwinger equations. Within t hese\napproaches QCD correlation functions of quarks\, gluon and hadrons a re computed\nnon-perturbatively from first principles.\n\nIn the present t alk I will discuss respective results for strongly-correlated vaccum QCD\, \nthe phase structure of QCD at finite temperature and density\, as well a s its dynamics\nclose to equilibrium. The talk concludes with a discussion of the further prospects\nfor our understanding of the phase structure an d dynamics of QCD.\n\nContact Person: Sebastian Diehl LOCATION:SR 0.03 TP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Marisol Ripoll DTSTART;TZID=Europe/Berlin:20180622T163000 DTEND;TZID=Europe/Berlin:20180622T173000 DTSTAMP:20260527T090436Z UID:0000001259@events.thp.uni-koeln.de DESCRIPTION:Marisol Ripoll\, ICS-2\, FZ Jülich\n\nPhoresis: from colloid drift to micromachines design\n\nFluids with an intrinsic gradient\, for e xample in their temperature\, charge\,\nor density distribution\, are know n to produce a directed drift in suspended\ncolloidal particles. This phen omenon is called phoresis. In this talk\, I\nwill summarize some recent th eoretical work with the main focus on\nthermophoresis\, mostly performed b y means of mesoscopic simulations. These\nstudies have also allow us to pr opose new applications in the design of\npromising phoretic machines such as microswimmers\, turbines\, or micropumps.\n\nContact Person: Joachim Kr ug LOCATION:TP seminar room 0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Andreas Klümper DTSTART;TZID=Europe/Berlin:20180713T163000 DTEND;TZID=Europe/Berlin:20180713T173000 DTSTAMP:20260527T090436Z UID:0000001263@events.thp.uni-koeln.de DESCRIPTION:Andreas Klümper\, Bergische Universität Wuppertal\n\nThe eff iciency of methodological detours: From vertex models to multi-component q uantum gases\n\nThe aim of this talk is two-fold. In the first part I want to explain how the study of interacting quantum gases in the continuum be nefits from tools developed for quantum systems on the lattice\, and how t hese tools appeared in the study of classical systems of the type of verte x models. These developments were carried out or were initiated by the man y research activities of Prof. J. Zittartz especially in the late 80s and the 90s. In passing I want to point out how matrix-product and tensor-netw ork states\nevolved in this environment and where the early exact and vari ational treatments led to.\n\nIn the second part I will investigate the th ermodynamics of the two-component one-dimensional Bose gas with contact in teractions in the vicinity of the quantum critical point separating the va cuum and the ferromagnetic liquid regime. The quantum critical region is f ound to belong to the universality\nclass of the spin-degenerate impenetra ble particle gas which\, surprisingly\, is very different from the single- component case.\n\nContact Person: Andreas Schadschneider LOCATION:SR 0.03 TP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Peter Zoller DTSTART;TZID=Europe/Berlin:20181015T140000 DTEND;TZID=Europe/Berlin:20181015T150000 DTSTAMP:20260527T090436Z UID:0000001311@events.thp.uni-koeln.de DESCRIPTION:Peter Zoller\, University of Innsbruck\n\nHybrid Classical-Qua ntum Simulations in the Innsbruck Quantum Cloud\n\nI will discuss recent d evelopments in quantum simulation of quantum many-body systems with atomic platforms from a theory perspective. Systems of interests include atoms i n optical lattices\, Rydberg atoms in optical tweezer arrays\, and trapped ions. Quantum simulation has so far been discussed as analog simulation\, where we physically build a system with the desired Hamiltonian\; or as d igital quantum simulation\, where time evolution of a many-body system is represented as a sequence of quantum gates on a quantum computer. I will a dd to this variation quantum simulation\, where a quantum feedback loop be tween a classical computer and an analog quantum simulator\, which acts as a quantum co-processor. As an example I will present results from an ongo ing theory - experiment collaboration in Innsbruck: here our quantum reso urce is a trapped-ion 20-qubit analog quantum simulator\, representing a t ransverse Ising model\, and we compute on the quantum device the ground an d excited states of the Lattice Schwinger Model as 1D Quantum Electrodynam ics. Remarkably\, variational quantum simulation allows "self-verification " of quantum results on the quantum machine\, as assessment of the error. As a second topic we will discuss novel measurement protocols for Rényi e ntropies\, and for out-of-time-ordered correlation functions (OTOCs)\, whi ch can be extracted from on statistical correlations between randomized me asurements. I will show a recent experiment with an ion chain\, demonstrat ing experimental observation of entanglement entropies in quench dynamics in 10 and 20 qubit devices. I will conclude my talk with a brief outlook on possible future directions\, including sub-wavelength optical lattices for atomic Hubbard models\, and quantum chemistry.\n\nContact Person: Seba stian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Stephanie Wehner DTSTART;TZID=Europe/Berlin:20181026T163000 DTEND;TZID=Europe/Berlin:20181026T180000 DTSTAMP:20260527T090436Z UID:0000001334@events.thp.uni-koeln.de DESCRIPTION:Stephanie Wehner\, QuTech\, Delft University of Technology\n\n Quantum Internet\n\nQuantum communication allows us to solve tasks that ar e provably\nimpossible using classical communication. A famous example is quantum\nkey distribution which enables secure communication. Here\, secur ity can\ndirectly be traced back to fundamental properties of quantum\nent anglement\, and is guaranteed even if an eavesdropper holds a quantum\ncom puter now or in the future. Many other applications have already been\nide ntified ranging from solving clock synchronization\, to exotic\napplicatio ns such as extending the baseline of telescopes to make better\nobservatio ns.\n\nIn this talk\, we will give an overview of the state of the art of\ nquantum communication\, and look at how quantum entanglement might help\n us to solve cryptographic problems. We continue to look ahead to some of\n the many challenges to be solved in order to realize large scale quantum\n networks\, which may eventually allow us to create entanglement between\na ny two points on earth yielding new insights to physics\, and bringing\nen tirely new internet applications.\n\nContact Person: David Gross LOCATION:HS II END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Nathan Goldman DTSTART;TZID=Europe/Berlin:20181109T163000 DTEND;TZID=Europe/Berlin:20181109T180000 DTSTAMP:20260527T090436Z UID:0000001317@events.thp.uni-koeln.de DESCRIPTION:Nathan Goldman\, Université libre de Bruxelles\n\nProbing Top ological Matter by «Heating»: From Quantized Circular Dichroism to Tenso r Monopoles\n\nThe intimate connection between topology and quantum physic s has been widely explored in solid-state physics\, revealing a plethora o f remarkable physical phenomena over the years. Building on their universa l nature\, topological properties are currently studied in an even broader context\, ranging from ultracold atomic gases to photonics\, where distin ct observables and probes offer a novel view on topological quantum matter .\nIn this talk\, I will discuss how the geometry of quantum states can be revealed using a universal scheme based on excitation-rate measurements u pon periodic driving [1\,2\,3]. When applied to Chern insulators or Landau levels\, this approach leads to a quantized circular dichroism phenomenon [1\,2]\, which can be interpreted as the dissipative counterpart of the q uantum Hall effect. Besides\, we will present protocols allowing for the e xperimental detection of the quantum metric tensor [3]\, which could be ap plied to detect new forms of monopoles in higher dimensions [4]. Finally\, I will report on the first experimental observation of quantized circular dichroism in an ultracold Fermi gas [5].\n\n[1] D. T. Tran\, A. Dauphin\, A. G. Grushin\, P. Zoller and N. Goldman\, Science Advances 3\, e1701207 (2017).\n[2] D. T. Tran\, N. R. Cooper\, and N. Goldman\, Phys. Rev. A 97\ , 061602(R) (2018).\n[3] T. Ozawa and N. Goldman\, Phys. Rev. B 97\, 20111 7(R) (2018).\n[4] G. Palumbo and N. Goldman\, arXiv:1805.01247(2018).\n[5] L. Asteria\, D. T. Tran\, T. Ozawa\, M. Tarnowski\, B. S. Rem\, N. Fläsc hner\, K. Sengstock\, N. Goldman and C. Weitenberg\, arXiv:1805.11077 (201 8).\n\nContact Person: Sebastian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Rodrigo Pereira DTSTART;TZID=Europe/Berlin:20181116T163000 DTEND;TZID=Europe/Berlin:20181116T180000 DTSTAMP:20260527T090436Z UID:0000001294@events.thp.uni-koeln.de DESCRIPTION:Rodrigo Pereira\, IIP\, Natal\n\nFrom quantum spin chains to c hiral spin liquids\n\nChiral spin liquids are highly entangled phases of i nteracting spins that break time reversal and inversion symmetries\, but l ack conventional magnetic order even at zero temperature. While chiral spi n liquids have not been unambiguously observed in nature yet\, they are ex pected to exhibit exotic properties following from a spectrum of fractiona l excitations. Theoretically\, chiral spin liquids are often described by strongly coupled gauge theories which are hard to tackle analytically beyo nd mean-field approximations. In this talk\, I will describe controllable approaches that allow us to understand various chiral spin liquids startin g from lower-dimensional building blocks\, namely arrays or junctions of H eisenberg spin chains. In the case of junctions\, I will discuss the conne ction between chiral spin liquids and chiral fixed points of boundary conf ormal field theory.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Assa Auerbach DTSTART;TZID=Europe/Berlin:20181127T163000 DTEND;TZID=Europe/Berlin:20181127T173000 DTSTAMP:20260527T090436Z UID:0000001347@events.thp.uni-koeln.de DESCRIPTION:Assa Auerbach\, Technion\n\nMax The Demon\n\n\n\nContact Perso n: Simon Trebst LOCATION:HS III END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Anja Metelmann DTSTART;TZID=Europe/Berlin:20190125T163000 DTEND;TZID=Europe/Berlin:20190125T180000 DTSTAMP:20260527T090436Z UID:0000001362@events.thp.uni-koeln.de DESCRIPTION:Anja Metelmann\, FU Berlin\n\nNonreciprocity in engineered qua ntum systems\n\nReciprocity is a fundamental symmetry in physics\; in opti cs it can be understood as\nthe principle of ‘if I can see you\, you can see me’. Breaking this symmetry results in asymmetric information trans fer between two systems\, i.e.\, the transmission amplitudes change under the exchange of source and detector. In the optimal situation\, informati on transfer only occurs in one direction\, which is a highly valuable feat ure for quantum information processing\, where one aims to read out a quan tum system while protecting the signal source. \n\nThe violation of the sy mmetry of reciprocity requires rather special conditions\, and one may ask the question if there is a general way to break reciprocity between two s ystems. This is indeed possible\, we find that one can construct nonrecipr ocal interactions by combining the appropriate coherent and dissipative dy namics. Our nonreciprocity concept was experimentally confirmed within an optomechanical array setup in a collaboration with Oscar Painter’s group at Caltech. Furthermore\, a number of related experiments can essentially be mapped to our approach as well. Overall\, the nonreciprocity protocol is a powerful tool for realize directional interactions between two quantu m systems and its full potential has yet to be explored. In this talk I gi ve an introduction of the basic concept on how\nto engineer nonreciprocal interactions and devices.\n\nContact Person: Sebastian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Debashish Chowdhury DTSTART;TZID=Europe/Berlin:20190201T163000 DTEND;TZID=Europe/Berlin:20190201T180000 DTSTAMP:20260527T090436Z UID:0000001360@events.thp.uni-koeln.de DESCRIPTION:Debashish Chowdhury\, IIT Kanpur\n\nUbiquity of Michaelis-Ment en input-output relation: conditions on the network of states\n\nThe input -output relations of a biological system summarize its functional characte ristics. Therefore\, answering many fundamental questions on biomolecular machines ultimately reduces to understanding their input-output relations. Enzymes\, that catalyze biochemical reactions\, are among the simplest ma chines for which both input and output are chemical in nature. Many enzyma tic reactions follow\nthe "Michaelis-Menten" relations between input conce ntrations and output concentration of the molecular species involved in th e reaction. We begin with a graph theoretic analysis of the input-output r elation of a single enzyme. Input-output response of a graph can be charac terized by the steady-state concentrations of the vertices. We present the conditions that must be satisfied by the structure of the graph (network) of states for the validity of the Michaelis-Menten input-output relation. This analysis sets the stage for understanding\, at the next level of com plexity\, the input-output relation of a\nmolecular machine\, that is a ma cromolecular complex\, and then at an even broader context of a group of i nteracting machines. I'll present an overview of our recent results on the se input-output relations at\nmultiple scales.\n\nContact Person: Joachim Krug LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | A.P. Young DTSTART;TZID=Europe/Berlin:20190503T163000 DTEND;TZID=Europe/Berlin:20190503T180000 DTSTAMP:20260527T090436Z UID:0000001372@events.thp.uni-koeln.de DESCRIPTION:A.P. Young\, UC Santa Cruz\n\nCan a Quantum Computer Solve Opt imization Problems More Efficiently than a Classical Computer?\n\nI will d iscuss ways in which the quantum world is different from\nthe classical wo rld\, and how these differences might be used to design quantum\ncomputers which are more powerful than classical computers\, at least for\ncertain problems. I shall focus on one approach to quantum computing\, called\nthe Quantum Adiabatic Algorithm\, which is used to solve optimization problem s\,\nwhich are of great importance in science\, engineering and industry.\ nAn optimization problem is one in which one has to minimize (or maximize) an\nenergy function in which there is competition between different terms .\nI will discuss results both from computer modelling of the Quantum Adia batic\nAlgorithm and real experiments on a device which has of order 1\,00 0\nsuperconducting quantum bits. The difficulty of getting a "quantum spe edup"\nfrom this device due to the great sensitivity of the ground state t o changes\nin parameters (chaos) will be discussed.\n\nContact Person: Tho mas Nattermann LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Dietrich Wolf DTSTART;TZID=Europe/Berlin:20190517T163000 DTEND;TZID=Europe/Berlin:20190517T180000 DTSTAMP:20260527T090436Z UID:0000001409@events.thp.uni-koeln.de DESCRIPTION:Dietrich Wolf\, Duisburg\n\nHow to convert a nano-powder into a nano-crystalline solid\n\nLargely unnoticed by theoretical physics\, the last 20 years have seen a revolution in nano-particle processing. One exa mple is that powders - although very porous\, when freshly produced - can be converted into a dense solid\, which still keeps a microstructure at th e nanoscale. The processes are new developments related to what traditiona lly was called "Spark Plasma Sintering"\, but has nothing to do with spark s and plasmas. Computer simulations predict intermediate steps of these pr ocesses and reveal the underlying mechanisms. I will give a review of rece nt simulations\, with a focus on so-called flash-sintering.\n\nContact Per son: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Philippe Corboz DTSTART;TZID=Europe/Berlin:20190614T163000 DTEND;TZID=Europe/Berlin:20190614T180000 DTSTAMP:20260527T090436Z UID:0000001385@events.thp.uni-koeln.de DESCRIPTION:Philippe Corboz\, University of Amsterdam\n\nStripes in the 2D Hubbard model and finite correlation length scaling with iPEPS\n\nAn infi nite projected entangled pair state (iPEPS) is a variational tensor networ k ansatz to represent 2D ground states in the thermodynamic limit where th e accuracy can be systematically controlled by the bond dimension D of the tensors. Thanks to several methodological advances in recent years\, iPEP S has become a very powerful tool for the study of 2D strongly correlated systems\, in particular models where quantum Monte Carlo fails due to the negative sign problem.\nIn the first part of my talk I will report on rece nt progress in simulating the 2D Hubbard model\, focussing on a particular ly challenging point in the phase diagram\, U/t=8 and 1/8 doping. A very c lose competition between several low-energy states is found\, including a uniform d-wave superconducting state and different types of stripe states. Systematic extrapolations to the exact\, infinite D limit show that the g round state is a period 8 stripe\, while stripes with periods 5-7 being ve ry close in energy. Consistent results are also obtained with density matr ix embedding theory\, density matrix renormalization group\, and constrain ed-path auxiliary field quantum Monte Carlo. On the other hand\, period 4 stripes - which are typically observed in experiments on the cuprates - ar e clearly higher in energy. However\, they become energetically favored up on adding a realistic next-nearest neighbor hopping term. \nIn the second part I will show how to systematically study 2D quantum critical phenomena with iPEPS using so-called finite correlation length scaling. This approa ch is very similar to conventional finite size scaling\, but instead of pe rforming the scaling analysis using different system sizes\, it is done ba sed on an effective correlation length extracted from the iPEPS. We apply this method to interacting spinless fermions on a honeycomb lattice at hal f filling and obtain a critical coupling and critical exponents which are in agreement with quantum Monte Carlo results.\n\nContact Person: Michael Scherer LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Alexander Altland DTSTART;TZID=Europe/Berlin:20190628T163000 DTEND;TZID=Europe/Berlin:20190628T180000 DTSTAMP:20260527T090436Z UID:0000001400@events.thp.uni-koeln.de DESCRIPTION:Alexander Altland\, Institute for Theoretical Physics\, Cologn e\n\nMany body quantum chaos of the Sachdev-Ye-Kitaev Model\n\nThe Sachdev -Ye-Kitaev (SYK) model describes a system of a large number of randomly in teracting Majorana fermions. It stands in the tradition of the random k-bo dy interaction models pioneered in nuclear physics and later applied in co ndensed matter contexts. The SYK model can be looked at from three interr elated perspectives: a) a system showing many body chaos and random matrix correlations\, b) a paradigm of strongly correlated (Majorana) quantum ma tter\, and c) the holographic shadow of a two-dimensional AdS2 gravitation al bulk. The interplay of these three has made it a focus of intensive res earch. Previous analytic work was restricted to the study of quantum corre lations at time scales short compared to the inverse of the many body leve l spacing. In this talk\, we address the complementary regime of large tim es. We will apply a matrix integral formalism to identify a set of collec tive modes in Fock space describing the relaxation of the system towards a n ergodic long time limit. We will discuss universal signatures of these m odes in spectral correlations\, and compare our results to numerics. Final ly\, we will discuss the structure of the system’s many body wave functi ons and point out differences to the wave functions of chaotic single par ticle systems.\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Andreas Laeuchli DTSTART;TZID=Europe/Berlin:20190712T163000 DTEND;TZID=Europe/Berlin:20190712T180000 DTSTAMP:20260527T090436Z UID:0000001428@events.thp.uni-koeln.de DESCRIPTION:Andreas Laeuchli\, Innsbruck\n\nFinite Correlation Length Scal ing in Lorentz-Invariant Gapless iPEPS Wave Functions\n\nIt is an open que stion how well tensor network states in the form of an infinite projected entangled-pair states (iPEPS) tensor network can approximate gapless quant um states of matter. In this talk we address this issue for two different physical scenarios: (i) a conformally invariant (2+1)d quantum critical po int in the incarnation of the transverse-field Ising model on the square l attice and (ii) spontaneously broken continuous symmetries with gapless Go ldstone modes exemplified by the S=1/2 antiferromagnetic Heisenberg and XY models on the square lattice. We find that the energetically best wave fu nctions display finite correlation lengths and we introduce a powerful fin ite correlation length scaling framework for the analysis of such finite b ond dimension (finite-D) iPEPS states. The framework is important (i) to u nderstand the mild limitations of the finite-D iPEPS manifold in represen ting Lorentz-invariant\, gapless many-body quantum states and (ii) to put forward a practical scheme in which the finite correlation length ξ(D) co mbined with field theory inspired formulas can be used to extrapolate the data to infinite correlation length\, i.e.\, to the thermodynamic limit. T he finite correlation length scaling framework opens the way for further e xploration of quantum matter with an (expected) Lorentz-invariant\, massle ss low-energy description\, with many applications ranging from condensed matter to high-energy physics.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Uwe Täuber DTSTART;TZID=Europe/Berlin:20191011T163000 DTEND;TZID=Europe/Berlin:20191011T180000 DTSTAMP:20260527T090436Z UID:0000001374@events.thp.uni-koeln.de DESCRIPTION:Uwe Täuber\, Virginia Tech\n\nTemperature Interfaces in the K atz-Lebowitz-Spohn Driven Lattice Gas\n\nWe explore the intriguing spatial patterns that emerge in a two-dimensional \nspatially inhomogeneous Katz- Lebowitz-Spohn (KLS) driven lattice gas with \nattractive nearest-neighbor interactions. The domain is split into two \nregions with hopping rates g overned by different temperatures T > T_c and \nT_c\, respectively\, where T_c indicates the critical temperature for phase \nordering\, and with th e temperature boundaries oriented perpendicular to the \ndrive. In the hot ter region\, the system behaves like the (totally) asymmetric\nexclusion p rocesses (TASEP)\, and experiences particle blockage in front of \nthe int erface to the critical region. To explain this particle density \naccumula tion near the interface\, we have measured the steady-state current in\nth e KLS model at T > T_c and found it to decay as 1/T. In analogy with TASEP \nsystems containing "slow" bonds\, transport in the high-temperature sub system \nis impeded by the lower current in the cooler region\, which tend s to set the \nglobal stationary particle current value. This blockage is induced by the \nextended particle clusters\, growing logarithmically with system size\, in the \ncritical region. We observe the density profiles i n both high-and low-\ntemperature subsystems to be similar to the well-cha racterized coexistence \nand maximal-current phases in (T)ASEP models with open boundary conditions\, \nwhich are respectively governed by hyperboli c and trigonometric tangent \nfunctions. Yet if the lower temperature is s et to T_c\, we detect marked \nfluctuation corrections to the mean-field d ensity profiles\, e.g.\, the \ncorresponding critical KLS power law densit y decay near the interfaces into \nthe cooler region. If the temperature i nterface is aligned parallel to the\ndrive\, we observe the cooler region to act as an absorbing sink for particle \ntransport\, with blockages emer ging at the subsystem boundaries.\n\nContact Person: Sebastian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Klaus Mecke DTSTART;TZID=Europe/Berlin:20191115T163000 DTEND;TZID=Europe/Berlin:20191115T180000 DTSTAMP:20260527T090436Z UID:0000001460@events.thp.uni-koeln.de DESCRIPTION:Klaus Mecke\, Friedrich-Alexander-Universität Erlangen-Nürnb erg\n\nSpace - Time - Matter: Finite Projective Geometry as a Quantum Worl d with Elementary Particles\n\nA unified theory for space-time and matter might be based on finite projective geometries instead of differentiable m anifolds and fields. Each point of the world is equipped with a quadratic form over a finite Galois field which define neighbors in the finite set o f points. Due to the projective equivalence of all quadratic forms this wo rld is necessarily a 4-dimensional\, locally Lorentz-covariant space-time with a gauge symmetry G(3)xG(2)xG(1) for internal points which represent elementary particle degrees of freedom. Thus\, matter appears as a geometr ic distortion of an inhomogeneous field of quadrics and all physical prope rties (spins\, charges) of the standard model seem to follow from its fini te geometric structure in a continuum limit. The finiteness inevitably in duces a fermionic quantization of all matter fields and a bosonic for gaug e fields. The main difference to Einstein's general theory of relativity i s the use of finite fields instead of real numbers to parametrize points o f events.\n\nContact Person: Joachim Krug LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Tobias Meng DTSTART;TZID=Europe/Berlin:20191129T163000 DTEND;TZID=Europe/Berlin:20191129T180000 DTSTAMP:20260527T090436Z UID:0000001462@events.thp.uni-koeln.de DESCRIPTION:Tobias Meng\, TU Dresden\n\nSemi-quantized quantum Hall states : gapless fractional states in quantum Hall bilayer\n\nRecent experiments in quantum Hall bilayer systems have revealed a new strongly correlated st ate: the semi-quantized quantum Hall state. This state arises in a bilayer quantum Hall system with strong interlayer-interactions\, has a quantized Hall resistance and vanishing longitudinal resistance\, while at the same time featuring a gapless sector that allows this state to exist for a con tinuum of filling factors. In this talk\, I will explain what a semi-quant ized quantum Hall state is\, and use a coupled-wire construction to predic t possible future experiments in the already existing experimental platfor ms.\n\nContact Person: Christoph Berke LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Aline Ramires DTSTART;TZID=Europe/Berlin:20191206T163000 DTEND;TZID=Europe/Berlin:20191206T180000 DTSTAMP:20260527T090436Z UID:0000001476@events.thp.uni-koeln.de DESCRIPTION:Aline Ramires\, ICTP\, Sao Paulo\, Brazil\n\nTwisted Bilayer G raphene: A novel platform for the engineering of exotic electronic states \n\nGraphene is one of the most versatile materials to realize exotic phen omena in condensed matter\, as a consequence of the emergent Dirac dispers ion at low energies. Introducing one more layer of complexity\, we find bi layer graphene\, which can be manipulated to achieve an arbitrary twist an gle between the two layers. Twisted bilayer graphene (TBG) has recently at tracted a lot of attention for the observed superconductivity and correlat ed electronic behavior at particular twist angles called magic angles. Her e\, I discuss two novel ways to control the electronic properties of twist ed bilayer graphene\, in particular:\n\n - Artificial gauge fields: We est ablished that the application of a homogeneous electric field perpendicula r to the bilayer is mathematically equivalent to a new kind of synthetic g auge field in the small twist angle regime. This identification opens the door for the generation and detection of pseudo-Landau levels in graphene platforms within robust setups\, which do not depend on strain engineering . Furthermore\, this new artificial gauge field leads to the development o f highly localized modes in emergent triangular or Kagome lattices\, assoc iated with flat bands close to charge neutrality.\n\n - Triple point Fermi ons: These are elusive electronic excitations that generalize Dirac and We yl modes beyond the conventional high energy paradigm. Yet\, finding real materials naturally hosting these excitations at the Fermi energy has rema ined a challenge. In this work\, we show how TBG can realize robust triple point fermions in two dimensions by the introduction of localized impurit ies.\n\nContact Person: Sebastian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Barbara Kraus DTSTART;TZID=Europe/Berlin:20200110T163000 DTEND;TZID=Europe/Berlin:20200110T180000 DTSTAMP:20260527T090436Z UID:0000001478@events.thp.uni-koeln.de DESCRIPTION:Barbara Kraus\, Innsbruck\n\nQuantum Information theory: from entanglement to quantum computing\n\nQuantum information theory combines c lassical information theory with quantum physics. This combination opens t he door to many fascinating applications which either do not have a class ical counterpart or outperform them. Prominent examples thereof are quantu m communication and quantum computation and simulations. Many of the appli cation are possible due to the subtle properties of quantum many-body syst ems. In particular entanglement\, which is a strong correlation among seve ral quantum systems\, plays an essential role.\n\nIn this talk\, I will fi rst present some recent results on multipartite entanglement theory. In pa rticular\, I will show that\ndeterministic local transformations among pur e n-partite d-level systems are almost never possible. The consequences of these findings in the context of entanglement theory will be discussed. T hen I will talk about certain aspects of quantum computations\, where enta nglement plays an important role. I will consider quantum algorithms which are composed of so-called matchgates. I will show that such an algorithm can always be compressed into an exponentially smaller quantum computation . However\, as will be explained\, the usage of an additional resource\, t he so-called magic states\, elevates such a computation to universal quant um computation\, while maintaining the same gate set. I will present the c haracterization of these magic states and discuss the consequences of thes e results in the context of quantum computation.\n\nContact Person: Sebast ian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Lode Pollet DTSTART;TZID=Europe/Berlin:20200117T163000 DTEND;TZID=Europe/Berlin:20200117T180000 DTSTAMP:20260527T090436Z UID:0000001482@events.thp.uni-koeln.de DESCRIPTION:Lode Pollet\, LMU Munich\n\nDiscerning multiple order paramete rs with interpretable machines: towards the automation of phase classifica tion\n\nMachine learning techniques can boost the exploration of complicat ed phase diagrams in many-body systems. To date\, most studies are tied to situations involving only one phase transition and one order parameter. S ystems accommodating multiple phases of coexisting and competing orders re main largely unexplored. Using Support Vector Machines (SVMs) we focus on multipolar orders and their tensorial order parameters\, whose identifica tion is difficult with traditional methods. The key property that allows o ne to make progress is the interpretability of the decision function\, fro m which the physical order parameter can be deduced. Furthermore\, we disc uss a second intrinsic parameter of the SVM\, the bias\, which allows one to make an unsupervised graph analysis of the topology of the phase diagra m. We illustrate our tool for the classical XXZ model on the frustrated py rochlore lattice. Unexpectedly\, the machine could also learn local constr aints hinting at various types of spin liquids resulting in a complete cla ssification of all types of behavior for this model.\n\nContact Person: Si mon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Gláucia Murta DTSTART;TZID=Europe/Berlin:20200424T163000 DTEND;TZID=Europe/Berlin:20200424T180000 DTSTAMP:20260527T090436Z UID:0000001495@events.thp.uni-koeln.de DESCRIPTION:Gláucia Murta\, Heinrich-Heine-Universität Düsseldorf\n\nDe vice-independent quantum cryptography: towards multipartite protocols\n\nQ uantum systems bring unprecedented advantages to the realization of classi cal cryptographic tasks. A remarkable example is quantum key distribution\ , which allows two parties\, Alice and Bob\, to establish a shared secret key that can be used for unconditionally secure communication. Furthermore \, the strong correlations exhibited by quantum systems can be explored to construct cryptographic protocols that are secure even when the parties a re completely ignorant about the internal working of their devices. This i s the device-independent paradigm. In this talk I will introduce the devic e-independent scenario and comment on recent results on device-independent quantum key distribution. Then I will move to the scenario of many partie s and discuss multipartite cryptographic tasks. Finally\, I will present n ew results on bounding the uncertainty of an eavesdropper in this setting\ , and discuss their application to multipartite cryptographic protocols.\n \nContact Person: D. Gross LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Michael Laessig DTSTART;TZID=Europe/Berlin:20200508T163000 DTEND;TZID=Europe/Berlin:20200508T180000 DTSTAMP:20260527T090436Z UID:0000001528@events.thp.uni-koeln.de DESCRIPTION:Michael Laessig\, University of Cologne\n\nSARS-CoV-2 — init ial observations on epidemiology and evolution\n\nThis talk will describe some current efforts to track\, understand\, and control the current coron a virus pandemic. We will review basic epidemiology and discuss the dynami cs of transmissions\, as well as monitoring efforts aimed to contain local outbreaks. We will also compare different scenarios of viral evolution.\n \nContact Person: David Gross and Joachim Krug LOCATION:Zoom END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Susanna Manrubia DTSTART;TZID=Europe/Berlin:20200612T163000 DTEND;TZID=Europe/Berlin:20200612T180000 DTSTAMP:20260527T090436Z UID:0000001530@events.thp.uni-koeln.de DESCRIPTION:Susanna Manrubia\, Centro Nacional de Biotecnologia\, Madrid\n \nPredictability: Can we precisely forecast the turning point and end of a n epidemic by fitting past data?\n\nNo\, we can’t. The time at which the growth in the number of infected individuals halts and starts decreasing cannot be calculated with certainty before the turning point is actually a ttained. This assertion is illustrated by adding to a standard SIR model a new class for confined individuals. A Bayesian fit to the on-going COVID- 19 pandemic in Spain shows that a slow-down in the number of newly infecte d individuals during the expansion phase allows to infer neither the preci se position of the maximum nor whether the measures taken will bring the p ropagation to the inhibition regime. Our study warns against precise forec asts of the evolution of epidemics based on mean-field\, effective models\ , and supports that only probabilities of different outcomes can be confid ently given.\n\nContact Person: Joachim Krug LOCATION:Online via Zoom END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Eva-Maria Graefe DTSTART;TZID=Europe/Berlin:20200619T163000 DTEND;TZID=Europe/Berlin:20200619T180000 DTSTAMP:20260527T090436Z UID:0000001534@events.thp.uni-koeln.de DESCRIPTION:Eva-Maria Graefe\, Imperial College\, London\n\nA Non-Hermitia n PT-symmetric kicked top\n\nA non-Hermitian PT-symmetric version of the k icked top is introduced to study the interplay of quantum chaos with balan ced loss and gain. The classical dynamics arising from the quantum dynamic s of the angular momentum expectation values are derived. It is demonstrat ed that the presence of PT-symmetry can lead to ''stable'' mixed regular c haotic behaviour without sinks or sources for subcritical values of the ga in-loss parameter. For large values of the kicking strength a strange attr actor is observed that also persists if PT-symmetry is broken. Classical s tructures are also identified in the quantum dynamics. Finally\, some of t he statistics of the eigenvalues of the quantum system are analysed.\n\nCo ntact Person: S. Diehl LOCATION:Online via Zoom END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Anne Nielsen DTSTART;TZID=Europe/Berlin:20200701T143000 DTEND;TZID=Europe/Berlin:20200701T153000 DTSTAMP:20260527T090436Z UID:0000001533@events.thp.uni-koeln.de DESCRIPTION:Anne Nielsen\, MPI-PKS Dresden\n\nAnyons as detector of topolo gy and phase transitions in 2D systems\, systems with fractal dimensions\, and quasicrystals\n\nSystems consisting of a large number of interacting bosons or fermions in two dimensions can in some situations form anyonic q uasiparticles that are neither bosons\, nor fermions. Such systems are top ologically ordered\, and they have many special properties. They are\, for instance\, not characterized by a local order parameter\, which makes it challenging to detect the phases.\n\nHere\, we demonstrate that anyons are an interesting tool to detect topological order in new types of systems a nd to detect phase transitions involving topological phases. The phase tra nsitions are detected based on the idea that the system does not support t he same types of quasiparticles on the two sides of the transition. We tes t the method on three rather different examples\, and in all cases we find that it is sufficient to study a simple property of the anyons\, requirin g low numerical costs\, to accurately detect the phase transition point. A further advantage of the method is that it does not require particular bo undary conditions\, and we utilize this to demonstrate that topological or der can also occur in fractal dimensions and on quasicrystals.\n\nReferenc es: arXiv:1909.02046\, arXiv:1907.03193\, PRB 101\, 115413 (2020).\n\nCont act Person: S. Diehl LOCATION:Online via Zoom !!please note the unusual date!! END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Raquel Queiroz DTSTART;TZID=Europe/Berlin:20200703T163000 DTEND;TZID=Europe/Berlin:20200703T180000 DTSTAMP:20260527T090436Z UID:0000001532@events.thp.uni-koeln.de DESCRIPTION:Raquel Queiroz\, Weizmann Institute\n\nTopological Crystalline Insulators: Boundary Topology\n\nIn this talk I will describe how topolog y emerges in crystalline environments from the perspective of local orbita ls and highlight subtleties which appear when characterizing topology prot ected by crystalline symmetry. I will introduce a new notion of a topologi cal obstruction which is not protected by bulk energy gap closings in peri odic boundary conditions\, but only in systems with open boundaries\, whic h we call boundary obstructed topological phases. We will describe in this context on a celebrated model - the quantized quadrupole insulator in two -dimensions.\n\nContact Person: S. Diehl LOCATION:Online via Zoom END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Peidong Yu DTSTART;TZID=Europe/Berlin:20200710T163000 DTEND;TZID=Europe/Berlin:20200710T180000 DTSTAMP:20260527T090436Z UID:0000001536@events.thp.uni-koeln.de DESCRIPTION:Peidong Yu\, DLR and ITP Cologne\n\nVelocity Distribution of G ranular Gases in Space\n\nWhile molecular gases are well described by esta blished kinetic theories\, when macroscopic granular particles replace mol ecules as the constituents in a granular gas\, new challenges arise due to the dissipative nature of their collisions. Including dissipation into th e theories leads to three main predictions: 1. non-Maxwellian velocity dis tributions\, 2. homogeneous cooling following the algebraic Haff's law an d 3. emergence of cluster instabilities. Experimental test of the theorie s requires (i) a low-gravity environment\, and (ii) external excitation of the granular particles that can drive them into a homogeneous spatial dis tribution. An experiment - Magnetically Excited Granular Matter (MEGraMa) - was developed at DLR to meet these demands and flown on board of parabol ic flights\, in a drop tower\, and on a sounding rocket. While the first t wo theoretical predictions can be demonstrated convincingly\, quantitative deviations between theory and experiment are apparent.\n\nContact Person: Joachim Krug LOCATION:Online via Zoom END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Karin Everschor-Sitte DTSTART;TZID=Europe/Berlin:20200717T163000 DTEND;TZID=Europe/Berlin:20200717T180000 DTSTAMP:20260527T090436Z UID:0000001550@events.thp.uni-koeln.de DESCRIPTION:Karin Everschor-Sitte\, Johannes Gutenberg University Mainz\n\ nMagnetic whirls for unconventional computing\n\nNovel computational parad igms in combination with proper hardware solutions are required to\noverco me the limitations of our state-of-the-art computer technology\, in partic ular regarding\nenergy consumption. Due to the inherent complex and non-li near nature\, spintronics offers the\npossibility towards energy-efficient \, non-volatile hardware solutions for various\nunconventional computing s chemes.[1-3]\n\nIn this talk\, I will discuss the possibility of using mag netic skyrmions for in particular two\nunconventional computing schemes – reservoir computing and stochastic computing.\nReservoir computing is a computational scheme that allows to simplify spatial-temporal\nrecogniti on tasks. We have shown that random skyrmion fabrics provide a suitable ph ysical\nimplementation of the reservoir[4\,5] and allow to classify patter ns via their complex resistance\nresponses either by tracing the signal ov er time or by a single spatially resolved\nmeasurement.[6] Stochastic comp uting is a computational paradigm that allows to speed up a\ncalculation w hile trading for numerical precision. Information is encoded in terms of b itstreams as a probability. A key requirement and simultaneously a challen ge is that the incoming\nbitstreams are uncorrelated. The Brownian motion of magnetic skyrmions allows creating a\ndevice that reshuffles the bit-st reams.[7\,8]\n\n[1] J. Grollier\, D. Querlioz\, K. Y. Camsari\, KES\, S. F ukami\, M. D. Stiles\, Nat. Electron. (2020)\n\n[2] E. Vedmedenko\, R. Kaw akami\, D. Sheka\, ...\, KES\, et al.\, J. of Phys. D (2020)\n\n[3] G. Fin occhio\, M. Di Ventra\, K.Y. Camsari\, KES\, P. K. Amiri and Z. Zeng\, arX iv:1907.04601\n\n[4] D. Prychynenko\, M. Sitte\, et al\, KES\, Phys. Rev. Appl. 9\, 014034 (2018)\n\n[5] G. Bourianoff\, D. Pinna\, M. Sitte and KES \, AIP Adv. 8\, 055602 (2018)\n\n[6] D. Pinna\, G. Bourianoff and KES\, ar Xiv:1811.12623\n\n[7] D. Pinna\, F. Abreu Araujo\, J.-V. Kim\, et al\, Phy s. Rev. Appl. 9\, 064018 (2018)\n\n[8] J. Zazvorka\, F. Jakobs\, D. Heinze \, ...\, KES\, et al.\, Nat. Nanotech. 14\, 658 (2019)\n\nContact Person: S. Diehl LOCATION:Online via Zoom END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Maia Garcia Vergniory DTSTART;TZID=Europe/Berlin:20201204T163000 DTEND;TZID=Europe/Berlin:20201204T180000 DTSTAMP:20260527T090436Z UID:0000001565@events.thp.uni-koeln.de DESCRIPTION:Maia Garcia Vergniory\, Donostia International Physics Center\ , Donostia-San Sebastian\, Spain Ikerbasque\, Basque Foundation for Scienc e\, Bilbao\, Spain\n\nBeyond Topological Quantum Chemistry\n\nTopological quantum chemistry (TQC) framework has provided a complete description of\n the universal properties of all possible atomic band insulators in all spa ce groups\nconsidering the crystalline unitary symmetries. It links the chemical and symmetry\nstructure of a given material with its topological properties. While this formalism filled\nthe gap between the mathematical classification and the practical diagnosis of\ntopological materials\, an obvious limitation is that it only applies to weakly interacting\nsystems. It is an open question to which extent this formalism can be generalized to\ncorrelated systems that can exhibit symmetry protected topological Mot t insulators.\nIn this talk I will first introduce TQC and its application and then I will address this question\nby combining cluster perturbation theory and topological Hamiltonians within TQC. This\nsimple formalism wil l be applied to calculate to the phase diagram of a representative\nmodel. The results are compared to numerically exact calculations from density m atrix\nrenormalization group and variational Monte Carlo simulations toget her with many-body\ntopological invariants.\n\nReferences\n1. M.G. Vergnio ry\, L. Elcoro\, C. Felser\, N. Regnault\, B.A. Bernevig\, Z.Wang\, “A c omplete catalogue of HighQuality Topological Materials“\, Nature 566\, 4 80-485 (2019) \n2. B. Bradlyn\, L. Elcoro\, J. Cano\, M.G. Vergniory\, Z. Wang\, C. Felser\, M.I. Aroyo\, B.A. Bernevig\, “Topological quantum ch emistry”\, Nature 547 (7663)\, 298-305 (2017).\n3. M. Iraola et al\, in preparation\n\nContact Person: Sebastian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Silvia Viola-Kusminskiy DTSTART;TZID=Europe/Berlin:20201211T163000 DTEND;TZID=Europe/Berlin:20201211T180000 DTSTAMP:20260527T090436Z UID:0000001568@events.thp.uni-koeln.de DESCRIPTION:Silvia Viola-Kusminskiy\, MPI Erlangen\n\nQuantum magnonics: Q uantum optics with magnons\n\nIn the last five years\, a new field has eme rged at the intersection between Condensed Matter and Quantum Optics\, den ominated “Quantum Magnonics”. This field strives to control the elemen tary excitations of magnetic materials\, denominated magnons\, to the leve l of the single quanta\, and to interface them coherently to other element ary excitations such as photons or phonons. The recent developments in thi s field\, with proof of concept experiments such as a single-magnon detect or\, have opened the door for hybrid quantum systems based on magnetic mat erials. This can allow us to explore magnetism in new ways and regimes\, h as the potential of unraveling quantum phenomena at unprecedented scales\, and could lead to breakthroughs for quantum technologies. A predominant r ole in these developments is played by cavity optomagnonic systems\, where an electromagnetic cavity\, either in the optical or microwave regime\, i s used to enhance and control the interaction between photons and magnons. In this talk\, I will introduce the field of Quantum Magnonics with empha sis on Cavity Optomagnonics\, and present some theoretical results from ou r group which aim to push the boundaries of the current state of the art.\ n\nContact Person: Sebastian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Jörg Schmiedmayer DTSTART;TZID=Europe/Berlin:20210507T163000 DTEND;TZID=Europe/Berlin:20210507T180000 DTSTAMP:20260527T090436Z UID:0000001613@events.thp.uni-koeln.de DESCRIPTION:Jörg Schmiedmayer\, Vienna Center for Quantum Science and Tec hnology (VCQ)\, Atominstitut\, TU-Wien\n\nEmergent Quantum Simulators\n\nQ uantum Simulation promises insight into quantum physics problems which are beyond the ability to calculate with conventional methods. Quantum simul ators can be built either using a ‘digital’ Trotter decomposition of t he problem or by directly building the Hamiltonian in the lab and performi ng ‘analogue’ experiments. I will present here a different approach\, by which the model to simulate emerges naturally from a completely differ ent microscopic Hamiltonian. I will illustrate this in the example of the emergence of the Sine-Gordon quantum field theory from the microscopic des cription of two tunnel coupled super fluids. Special emphasis will be put on how to verify such emergent quantum simulators and how to characterize them. Thereby I will present two tools: High order correlation functions and their factorization [1]\, the evaluation of the quantum effective acti on and the momentum dependence of propagators and vertices (running coupli ngs\, renormalization of mass etc ..) of the emerging quantum field theory [2] and quantum field tomography that points to a new way to read out qua ntum simulators [3]. Together they establish general methods to analyse qu antum systems through experiments and thus represents a crucial ingredient towards the implementation and verification of quantum simulators.\n\nWor k performed in collaboration with the groups of Th. Gasenzer und J. Berges (Heidelberg)\, Jens Eisert (FU Berlin) and E. Demler (Harvard). Supported by the DFG-FWF: SFB ISOQUANT: and the EU: ERC-AdG QuantumRelax\n\n[1] T. Schweigler et al.\, Nature 545\, 323 (2017)\, arXiv:1505.03126\n[2] T. Zac he et al. Phys. Rev. X 10\, 011020 (2020) \n[3] M. Gluza et al.\, Communic ation Physics 3\, 12 (2020)\n\nContact Person: Matteo Rizzi LOCATION:https://uni-koeln.zoom.us/j/95980214300 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Erwin Frey DTSTART;TZID=Europe/Berlin:20210604T163000 DTEND;TZID=Europe/Berlin:20210604T180000 DTSTAMP:20260527T090436Z UID:0000001633@events.thp.uni-koeln.de DESCRIPTION:Erwin Frey\, LMU München\n\nTopological Phase Transitions in Population Dynamics\n\nTopological phases were discovered in condensed mat ter physics and recently extended to classical physics such as topological mechanical metamaterials. Their study and realization in soft-matter and biological systems has only started to develop. In this talk we discuss ho w topological phases may determine the behavior of nonlinear dynamical sys tems that arise\, for example\, in population dynamics. We have shown that topological phases can be realized with the anti-symmetric Lotka-Volterra equation (ALVE). The ALVE is a paradigmatic model system in population dy namics and governs\, for example\, the evolutionary dynamics of zero-sum g ames\, such as the rock-paper-scissors game [1]\, but also describes the c ondensation of non-interacting bosons in driven-dissipative set-ups [2]. W e have shown that for the ALVE\, defined on a one-dimensional chain of roc k-paper-scissors cycles\, robust polarization emerges at the chain’s edg e [3]. The system undergoes a transition from left to right polarization a s the control parameter passes through a critical value. At the critical p oint\, solitary waves are observed. We found that the polarization states are topological phases and that this transition is indeed a topological ph ase transition. Remarkably\, this phase transition falls into symmetry cla ss D within the “ten-fold way” classification scheme of gapped free-fe rmion systems\, which also applies\, for example\, to one-dimensional topo logical superconductors. Beyond the observation of topological phases in t he ALVE\, it might be possible to generalize the approach of our work to o ther dynamical systems in biological physics whose attractors are nonlinea r oscillators or limit cycles.\n\n[1] J. Knebel\, T. Krüger\, M. F. Weber \, and E. Frey\, Phys. Rev. Lett. 110\, 168106 (2013).\n[2] J. Knebel\, M. F. Weber\, T. Krüger\, and E. Frey\, Nature Communications 6\, 6977 (201 5).\n[3] J. Knebel\, P. M. Geiger\, and E. Frey\, Phys. Rev. Lett. (in pre ss) [arXiv:2009.01780].\n\nContact Person: Joachim Krug LOCATION:Online via zoom END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Verleihung des ‘Federico Tonielli Awards’ DTSTART;TZID=Europe/Berlin:20210611T170000 DTEND;TZID=Europe/Berlin:20210611T180000 DTSTAMP:20260527T090436Z UID:0000001628@events.thp.uni-koeln.de DESCRIPTION:Verleihung des ‘Federico Tonielli Awards’\n\n\n\n\n\nConta ct Person: Sebastian Diehl LOCATION:Zoom END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Lidia Del Rio DTSTART;TZID=Europe/Berlin:20210618T163000 DTEND;TZID=Europe/Berlin:20210618T180000 DTSTAMP:20260527T090436Z UID:0000001612@events.thp.uni-koeln.de DESCRIPTION:Lidia Del Rio\, ETHZ\n\nThe thermodynamics of quantum computin g\n\nAs physical implementations of small quantum computers become a reali ty\, we investigate two common bottlenecks: limited memory size and noise caused by heat dissipation. In this talk I will go over the theoretical fu ndamentals behind heat production in quantum information processing\, and how it can be alleviated without a large cost in terms of quantum memory r equirements. The talk will be accessible to non-experts\, familiar with qu antum mechanics.\n\nLandauer posited that irreversible information-process ing operations (like the erasure of a classical or quantum memory at the e nd of a computation) have an intrinsic thermodynamic work cost\, which is associated with heat dissipation to the environment [1]. In the case of a quantum computer this heat dissipation is particularly undesirable\, as th e computer relies on cooling to keep coherence of quantum states. Bennett proposed a solution: if we run the circuit up until the final measurement s and then reverse it\, we keep heat production to a theoretical minimum [ 2]. However\, this proposal has a cost in terms of quantum memory: none of the quantum registers that are only needed for parts of the computation c an be freed until the very end. In the intermediate term\, when we have on ly a few hundreds of qubits in a quantum memory\, this is a bottleneck for parallelization of quantum computations: we have to wait to finish an alg orithm before we can free the memory to run another. In recent work\, we t ry to ameliorate this problem by investigating "online erasure" of quantum registers that are no longer needed for a given algorithm. That way\, we could free up quantum memory already halfway through a computation. We stu dy the minimal cost of erasure in these scenarios\, using results on the e rasure of entangled quantum registers [3]. For a specific class of algorit hms (the hidden subgroup problem) we find optimal online erasure protocols \, and see how we could use them to optimize the algorithms [4].\n\nContac t Person: Sebastian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Xiaoyu Dong DTSTART;TZID=Europe/Berlin:20211029T163000 DTEND;TZID=Europe/Berlin:20211029T180000 DTSTAMP:20260527T090436Z UID:0000001647@events.thp.uni-koeln.de DESCRIPTION:Xiaoyu Dong\, Uni Gent\n\nSome discussions about spin-1 and sp in-orbital Kitaev models\n\nThis talk includes two works that have relatio n to the Kitaev model on the honeycomb lattice. In the first part\, I will focus on the properties of the spin-1 Kitaev model\, and discuss the cont roversial results about whether the spin-1 model is gapless. In the second part\, I will talk about the spin-orbital generalizations of the Kitaev m odel\, and transitions between topological phases featuring emergent fract ionalized excitations. \n\nReference:\n1. Physical Review B 102\, 121102 ( R) (2020) \n2. Physical Review Letters 125\, 257202 (2020)\n\nContact Pers on: Sebastian Diehl LOCATION:Zoom END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Joachim Krug DTSTART;TZID=Europe/Berlin:20211105T163000 DTEND;TZID=Europe/Berlin:20211105T180000 DTSTAMP:20260527T090436Z UID:0000001667@events.thp.uni-koeln.de DESCRIPTION:Joachim Krug\, IBP\, UoC\n\nRecords and extremes in a changing climate\n\nA record is an entry in a time series that is greater or small er than all previous entries. The public perception of climate change is p articularly sensitive to record-breaking weather events\, which often rece ive extensive media coverage. As a consequence\, a number of recent studie s have been aimed at detecting and quantifying the effects of a warming cl imate on the frequency of temperature records. The mathematical theory of records makes universal and sometimes counter-intuitive predictions about the temporal statistics of record events\, but it is largely restricted to stationary time series. After an introduction to the classic theory\, I w ill explain the extensions needed to deal with trends\, and\nthe effect of warming on temperature records will be described at different levels of r esolution. In the last part of the talk I will discuss time series of prec ipitation records\, where the presence of dry days of zero precipitation i nduces nontrivial correlations between record-breaking events.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | David Luitz DTSTART;TZID=Europe/Berlin:20211112T163000 DTEND;TZID=Europe/Berlin:20211112T180000 DTSTAMP:20260527T090436Z UID:0000001644@events.thp.uni-koeln.de DESCRIPTION:David Luitz\, MPI-PKS Dresden / Uni Bonn\n\nRandom matrix theo ry for strongly dissipative quantum many-body systems\n\nQuantum systems a re generally extremely hard to isolate from their\n environment\, even mor e so if we want to exert control or perform\n measurements. It is therefor e important to understand the effect of\n the coupling to the environment. I will discuss a random matrix\n approach to quantum many-body systems wi th strong dissipation and\n show that the locality of dissipation processe s gives rise to a\n hierarchy of relaxation timescales\, which can be expe rimentally\n observed. This theory can also be applied to the case of a s trong\n variance in dissipation strengths\, which can lead to an emerging set\n of metastable states.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Annette Zippelius DTSTART;TZID=Europe/Berlin:20220114T163000 DTEND;TZID=Europe/Berlin:20220114T180000 DTSTAMP:20260527T090436Z UID:0000001674@events.thp.uni-koeln.de DESCRIPTION:Annette Zippelius\, Georg-August-Universitat Göttingen\n\nEme rgence of Long-Ranged Stress Correlations at the Liquid to Glass Transitio n\n\nA theory for the nonlocal shear stress correlations in supercooled li quids and colloidal suspensions is derived from first principles. It captu res the crossover from viscous to elastic dynamics at an idealized liquid to glass transition and explains the emergence of long-ranged stress corre lations in glass\, as expected from classical continuum elasticity. Wherea s Eshelby‘s elasticity pattern is recovered independently of the dynamic s\, the Goldstone modes differ drastically: Newtonian dynamics leads to pr opagating transverse sound\, while the Goldstone modes of a colloidal glas s are diffusive. Precursors of the long-ranged anisotropic stress correlat ions in the fluid can be observed in both cases. Their spatial extent can be characterized by a correlation length\, which grows like the shear visc osity for a Newtonian fluid and like its square root in a colloidal fluid. These results\nare derived within a hydrodynamic theory\, generalising Ma xwell‘s model to finite wavenumbers\, after the dynamics has been decomp osed into potentially slow modes\, associated with conservation laws and/o r the order parameter\, and fast microscopic degrees of freedom.\n\nContac t Person: Martin Zirnbauer LOCATION:Online via zoom END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Michael Buchhold DTSTART;TZID=Europe/Berlin:20220422T163000 DTEND;TZID=Europe/Berlin:20220422T180000 DTSTAMP:20260527T090436Z UID:0000001714@events.thp.uni-koeln.de DESCRIPTION:Michael Buchhold\, Institute for Theoretical Physics\, Univers ity of Cologne\n\nDriven Rydberg atoms: A platform to study criticality\, self-organization and emergent network structures in atomic excitations\n\ nLaser-induced optical excitation of hydrogen-like alkaline and alkalineea rth\natoms can be used to create arrays of highly controllable Rydberg\nst ates\, which are promising candidates for atom-based quantum\ncomputation and for realizing new many-body phenomena. In a gas of\natoms\, the interp lay between the laser-drive and strong interactions\nbetween Rydberg state s yields new cooperative effects\, including either\nthe complete blocking or the facilitation of excitations by a nearby\nRydberg state. I will dis cuss theoretical and experimental approaches to\nthe so-called facilitatio n regime\, in which the creation of excitations is\nconditioned on the pre sence of a nearby Rydberg state. This gives rise to\na kinetically constra ined dynamics\, supporting the avalanche-like\nspreading of excitations an d a non-equilibrium phase transition into an\nabsorbing state with zero ex citations. The interplay of interactions\, laserdrive\,\ndissipation and a tomic motion\, each acting on their individual timescale\,\ngives rise to a multifaceted dynamics. It ranges from an epidemiclike\nspreading of exci tations on an emergent complex network at short\ntimes to a long-lived cri tical regime of repeated scale invariant excitation\navalanches\, reminisc ent of self-organized criticality\, at late times.\n\nContact Person: Seba stian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Simone Montangero DTSTART;TZID=Europe/Berlin:20220610T163000 DTEND;TZID=Europe/Berlin:20220610T180000 DTSTAMP:20260527T090436Z UID:0000001731@events.thp.uni-koeln.de DESCRIPTION:Simone Montangero\, University of Padua\, Italy\n\nTensor netw ork algorithms for high-dimensional quantum many-body systems\n\nWe review some recent results on the development of efficient unconstrained tree te nsor network algorithms and their applications to high-dimensional many-bo dy quantum systems and machine learning problems in High Energy Physics. I n particular\, we present results on topological two-dimensional systems\, two dimensional Rydberg atom systems\, and two and three-dimensional latt ice gauge theories in presence of fermonic matter. Finally\, we present th eir application to LHCb event classification and to the study of open many -body quantum systems\, specifically to the computation of the entanglemen t of formation in critical many-body quantum systems at finite temperature .\n\nContact Person: Matteo Rizzi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Paolo Politi DTSTART;TZID=Europe/Berlin:20221014T163000 DTEND;TZID=Europe/Berlin:20221014T180000 DTSTAMP:20260527T090436Z UID:0000001740@events.thp.uni-koeln.de DESCRIPTION:Paolo Politi\, Istituto dei Sistemi Complessi\, Florence\n\nA condensation transition at equilibrium and out-of-equilibrium\n\nSeveral l attice models display a condensation transition in real space when the den sity of a suitable order parameter exceeds a critical value. At equilibriu m there are well established results and we discuss different scenarios of the condensation transition. In the out-of-equilibrium setup we consider one of such model with two conservation laws\, attached to two external re servoirs\,\nR_1 and R_2. Both reservoirs impose subcritical boundary condi tions: When R_1=R_2 the system is in equilibrium below the localization th reshold and no condensate appears. Instead\, when R_1 differs from R_2 loc alization may arise in an internal portion of the lattice. This phenomenon is due to the coupled transport of two conserved quantities. In collabora tion with Gabriele Gotti and Stefano Iubini.\n\nContact Person: Joachim Kr ug LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Tobias Stollenwerk DTSTART;TZID=Europe/Berlin:20221021T163000 DTEND;TZID=Europe/Berlin:20221021T180000 DTSTAMP:20260527T090436Z UID:0000001761@events.thp.uni-koeln.de DESCRIPTION:Tobias Stollenwerk\, Forschungszentrum Jülich\n\nDiagrammatic Analysis of near-term Quantum Optimization Algorithms\n\nThere are few ca ndidates for quantum algorithms which might outperform\nclassical approach es while being amenable to noisy quantum computing\ndevices.\nBeside quant um simulation algorithms\, quantum algorithms for approximate\noptimizatio n are promising candidates.\nThe target application for these approaches i s finding approximate\nsolutions to combinatorial optimization problems.\n In this talk I will give an overview on quantum approximate optimization\n approaches\,\nwhile mainly focusing on the quantum approximate optimizatio n algorithm\n(QAOA)\, quantum annealing and variations thereof.\nI will de monstrate these concepts by considering a particular real-world\nplanning problem\, the flight-gate assignment problem [1].\nIn addition\, I will co ver novel approaches for the diagrammatic analysis\nof parametrized quantu m circuits\, like QAOA.\nHere I will demonstrate how such methods can be e mployed to help with\nthe performance investigation of QAOA and other vari ational quantum\nalgorithms.\n\n[1] https://ieeexplore.ieee.org/document/9 222273\n[2] https://arxiv.org/abs/2204.01307\n\nContact Person: David Gros s LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Jens Elgeti DTSTART;TZID=Europe/Berlin:20221028T163000 DTEND;TZID=Europe/Berlin:20221028T180000 DTSTAMP:20260527T090436Z UID:0000001779@events.thp.uni-koeln.de DESCRIPTION:Jens Elgeti\, FZ Jülich\n\nActive Matter driven by Growth\n\n Active matter is matter driven out of equilibrium by its microscopic const ituents. Common examples include the cytoskeleton of the cell\, bacteria s wimming in a fluid\, or herds of wildebeest on the African planes. In thes e systems\, the constituents create forces and motion driving the system o ut of equilibrium. But now imagine cells dividing or a tumor growing. Then activity does not enter the dynamics via the forces\, but by material con servation. The material generates itself. In order to grow\, cells must ex ert mechanical pressure on the neighboring tissue. In turn\, mechanical st ress influences growth and may play a role in cell competition. This insig ht has led to the notion of homeostatic pressure – the pressure exerted by a tissue in homeostasis. We use particle based computer simulations to model growing tissues. Surprisingly\, we find that when cross interactions are taken into account\ntissues with different homeostatic pressure can c oexist and the evolution can favor the weaker tissue\, or even results in tumor heterogeneity.\n\nContact Person: Joachim Krug LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Leonardo Mazza DTSTART;TZID=Europe/Berlin:20221125T163000 DTEND;TZID=Europe/Berlin:20221125T180000 DTSTAMP:20260527T090436Z UID:0000001777@events.thp.uni-koeln.de DESCRIPTION:Leonardo Mazza\, LPTMS - Université Paris-Saclay\n\nA spin-st atistics relation for the quasiparticles of quantum Hall states\n\nWe prov e a generic spin-statistics relation for the fractional quasiparticles tha t appear in quantum\nHall planar setups. The proof is based on an efficien t way for computing the Berry phase acquired\nby a generic quasiparticle t ranslated in the plane along a circular path\, and on the crucial fact tha t\nonce the gauge-invariant generator of rotations is projected onto a Lan dau level\, it fractionalizes\namong the quasiparticles and the edge. Usin g these results we define a measurable quasiparticle\nfractional spin that satisfies the spin-statistics relation. As an application\, we predict th e value\nof the spin of the composite-fermion quasielectron proposed by Ja in\; our numerical simulations\nagree with that value. We also show that t he difficulties encountered when studying the statistical\nproperties of L aughlin’s quasielectron can be traced back to a spin that does not satis fy the spin-\nstatistics relation. We conclude with some remarks on the to tal angular momentum of the system\nas a function of the quasiparticle pos itions and on an ambiguity in the definition of the spin. Further results on the non-Abelian anyons of the Moore-Read wavefunction will be presented .\n\nReferences\n[1] A. Nardin\, E. Ardonne and LM\, unpublished\n[2] Comp arin\, Biella\, Opler\, Macaluso\, Polychronakos\, LM\, PRB 105 085125 (20 22)\n[3] Macaluso\, Comparin\, LM\, Carusotto\, PRL 123 266801 (2020)\n\nC ontact Person: Matteo Rizzi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Muhittin Mungan DTSTART;TZID=Europe/Berlin:20221216T163000 DTEND;TZID=Europe/Berlin:20221216T180000 DTSTAMP:20260527T090436Z UID:0000001781@events.thp.uni-koeln.de DESCRIPTION:Muhittin Mungan\, IBP\, University of Cologne\n\nMemory Format ion in Driven Disordered Systems - Dead or Alive\n\nMemory formation and a geing are abundant in many soft matter systems. The disorder underlying th ese systems gives rise to a rich energy landscape\, consisting of a large number of metastable states. These landscapes are accompanied by a plethor a of pathways\, along which such systems can evolve when exposed to a vary ing temperature or mechanical load. The resulting dynamics can be rather c omplex\, giving rise to dynamically critical phenomena such as irreversib ility and yielding. At the same time\, such system exhibit parallels with the adaptive evolution of biological populations in time-varying environme nts. In this talk I will present a general framework to analyze the dynami cs and memory formation of driven disordered systems. I will then show how this framework can be applied to understand both the response of a cyclic ally sheared amorphous solid\, as well as the antibiotic resistance evolut ion of a microbial population subject to time-varying drug concentrations. \n\nContact Person: Joachim Krug LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Frank Wilhelm-Mauch DTSTART;TZID=Europe/Berlin:20230120T163000 DTEND;TZID=Europe/Berlin:20230120T180000 DTSTAMP:20260527T090436Z UID:0000001778@events.thp.uni-koeln.de DESCRIPTION:Frank Wilhelm-Mauch\, FZ Julich\n\nTwo improvements of NISQ Qu antum Algorithms\n\nIn the NISQ era\, we are looking to approach quantum a dvantage with shallow algorithms\, which are often variational in nature. In those cases\, proofs of speedup are hard to come by and a lot of resear ch is empirical. A particularily relevant case here is the Quantum Approxi mate Optimization Algorithm (QAOA). I will present its semiclassical limit \, mean-field QAOA\, which can be classically simulated and present a crit erion for its applicability\, hence allowing to identify cases when full Q AOA is not promising. Another relevant case is the study of quantum manybo dy systems with digital algorithms. Here\, I will show an improved\, physi cs-inspired algorithm to sample the key observable for studying theses sys tems\, the single-particle Green’s function. \n\nWork with Dmitry Bagret s\, Aditi Misra-Spieldenner\, Tobias Stollenwerk\, Tim Bode\, Peter Schuhm acher\, David Headley\, and Gino Bishop\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Hidetoshi Nishimori DTSTART;TZID=Europe/Berlin:20230419T143000 DTEND;TZID=Europe/Berlin:20230419T160000 DTSTAMP:20260527T090436Z UID:0000001826@events.thp.uni-koeln.de DESCRIPTION:Hidetoshi Nishimori\, Tokyo Institute of Technology\n\nQuantum simulation by quantum annealing\n\nThe field of quantum annealing is unde rgoing a rapid development in terms of its application to quantum simulati ons. In this talk\, I will first give an overview of quantum annealing wi th some emphasis on real-world applications. I then describe our recent wo rk on coherent quantum simulation to experimentally test the Kibble-Zurek mechanism for the 1d transverse-field Ising model [1].\n\n[1] A. King et a l\, Nature Phys. 18\, 1324 (2022)\nhttps://www.nature.com/articles/s41567- 022-01741-6\n\nContact Person: Simon Trebst LOCATION:Seminar Room of the Institute of Physics II END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Scuola Normale Superiore\, Pisa and THP DTSTART;TZID=Europe/Berlin:20230526T163000 DTEND;TZID=Europe/Berlin:20230526T180000 DTSTAMP:20260527T090436Z UID:0000001792@events.thp.uni-koeln.de DESCRIPTION:Scuola Normale Superiore\, Pisa and THP\n\nTonielli Award 2023 \n\n\n\nContact Person: Sebastian Diehl LOCATION:Aula 2\, University main building END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Pasquale Calabrese DTSTART;TZID=Europe/Berlin:20230609T154500 DTEND;TZID=Europe/Berlin:20230609T170000 DTSTAMP:20260527T090436Z UID:0000001831@events.thp.uni-koeln.de DESCRIPTION:Pasquale Calabrese\, SISSA\n\nThe quantum Mpemba effect\n\nThe Mpemba effect is the counterintuitive and controversial phenomenon that h ot water cools faster than cold one. Here I will introduce an analogous ef fect recently proposed and observed in extended quantum systems in which a symmetry is explicitly broken by the initial state\, but it is restored b y the time evolution. To study this phenomenon we introduce a new quantity \, dubbed entanglement asymmetry\, which is a measure of symmetry breaking inspired by the theory of entanglement in many-body states.\n\nContact Pe rson: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Hartmut Löwen DTSTART;TZID=Europe/Berlin:20230623T163000 DTEND;TZID=Europe/Berlin:20230623T180000 DTSTAMP:20260527T090436Z UID:0000001819@events.thp.uni-koeln.de DESCRIPTION:Hartmut Löwen\, HHU Düsseldorf\n\nStatistical theories of ba cterial growth\n\nAfter a general introduction in dynamical density functi onal theory (DDFT) we show that this theory provides a versatile tool to d escribe bacterial colonies. We formulate the growth and division of bacter ia within a DDFT framework and include the effect of dynamical mechano-sel f-regulation of cell size. Theoretical predictions are compared to particl e-resolved computer simulations and to experiments. The theory is generali zable to binary systems as well.\n\nContact Person: Joachim Krug LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Johannes Knolle DTSTART;TZID=Europe/Berlin:20230630T163000 DTEND;TZID=Europe/Berlin:20230630T180000 DTSTAMP:20260527T090436Z UID:0000001837@events.thp.uni-koeln.de DESCRIPTION:Johannes Knolle\, TU Munich\n\nAnomalous Quantum Oscillations in Metals and Insulators\n\nQuantum oscillation phenomena describe the per iodic variation of thermodynamic and transport properties of materials as a function of magnetic field. Since their discovery in 1930\, their observ ation is commonly assumed to be a definite sign for the presence of a Ferm i surface (FS) in a metal. Indeed\, the effect forms the basis of a well-e stablished experimental procedure for accurately measuring FS topology and geometry of metallic systems. In this talk I will discuss recent developm ents which challenge the canonical description of quantum oscillations. I will first review our work on quantum oscillations in insulators. Next\, I will discuss the possibility of sharp quantum oscillation frequencies in metals which do not correspond to Fermi surface orbits and the effect of s trong electron interactions. Finally\, I will present experimental results confirming our theoretical predictions and discuss the broader implicatio ns of anomalous quantum oscillations.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Christian Schilling DTSTART;TZID=Europe/Berlin:20230714T163000 DTEND;TZID=Europe/Berlin:20230714T180000 DTSTAMP:20260527T090436Z UID:0000001852@events.thp.uni-koeln.de DESCRIPTION:Christian Schilling\, Arnold Sommerfeld Centre for Theoretical Physics\, LMU Munich\n\nThe Electron Correlation Problem from a Quantum I nformation Perspective\n\nDescribing strongly interacting electrons is one of the crucial challenges of modern quantum physics. A comprehensive solu tion to this electron correlation problem would simultaneously exploit bot h the pairwise interaction and its spatial decay. By taking a quantum info rmation perspective\, we explain how this structure of realistic Hamiltoni ans gives rise to two conceptually different notions of correlation and en tanglement. The first one describes correlations between orbitals while th e second one refers more to the particle picture. We illustrate those two concepts of orbital and particle correlation and present measures thereof. Our results for different molecular systems reveal that the total correla tion between molecular orbitals is mainly classical\, raising questions ab out the general significance of entanglement in chemical bonding. Finally\ , we also speculate on a promising relation between orbital and particle c orrelation and explain why this may replace the obscure but widely used co ncept of static and\ndynamic correlation.\n\nContact Person: Matteo Rizzi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Frank Pollmann DTSTART;TZID=Europe/Berlin:20231103T163000 DTEND;TZID=Europe/Berlin:20231103T180000 DTSTAMP:20260527T090436Z UID:0000001857@events.thp.uni-koeln.de DESCRIPTION:Frank Pollmann\, TU Munich\n\nEntanglement Transitions in Unit ary Circuit Games\n\nRepeated projective measurements in unitary circuits can lead to an entanglement phase transition as the measurement rate is tu ned. In this work\, we consider a different setting in which the projectiv e measurements are replaced by dynamically chosen unitary gates that minim ize the entanglement. This can be seen as a one-dimensional unitary circui t game in which two players get to place unitary gates on randomly assigne d bonds at different rates: The “entangler” applies a random local uni tary gate with the aim of generating extensive (volume law) entanglement. The “disentangler”\, based on limited knowledge about the state\, choo ses a unitary gate to reduce the entanglement entropy on the assigned bond with the goal of limiting to only finite (area law) entanglement. In orde r to elucidate the resulting entanglement dynamics\, we consider three dif ferent scenarios: (i) a classical discrete height model\, (ii) a Clifford circuit\, and (iii) a general Haar random unitary circuit. We find that bo th the classical and Clifford circuit models exhibit phase transitions as a function of the rate that the disentangler places a gate\, which have si milar properties that can be understood through a connection to the stocha stic Fredkin chain. In contrast\, the “entangler” always wins when usi ng Haar random unitary gates and we observe extensive\, volume law entangl ement for all non-zero rates of entangling.\n\nContact Person: not specifi ed LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Claudio Castelnovo DTSTART;TZID=Europe/Berlin:20231110T163000 DTEND;TZID=Europe/Berlin:20231110T180000 DTSTAMP:20260527T090436Z UID:0000001856@events.thp.uni-koeln.de DESCRIPTION:Claudio Castelnovo\, Cambridge University\n\nDynamical fractal and anomalous noise in a clean magnetic crystal\n\nFractals — objects w ith non-integer dimensions — occur in manifold settings and length scale s in nature\, ranging from snowflakes and lightning strikes to natural coa stlines. Much effort has been expended to generate and study fractals in m any-body physics\, oftentimes underpinned by the presence of disorder. Her e\, we identify an emergent dynamical fractal in a disorder-free\, stoichi ometric three-dimensional magnetic crystal in thermodynamic equilibrium. T he phenomenon is borne out of constraints on the dynamics of the microscop ic degrees of freedom imposed by the topological nature of the system and by its characteristic point-like excitations\, which at low temperatures b ecome restricted to move on the fractal. This observation explains the ano malous exponent found in magnetic noise experiments on Dy2Ti2O7\, and it r esolves a long standing puzzle about its rapidly diverging relaxation time . This is a case in point of the capacity of even simple topological many- body systems to exhibit striking phenomena in their cooperative dynamics\, and of the promise they hold for further surprising discoveries.\n\nConta ct Person: Alexander Altland LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Henning Schomerus DTSTART;TZID=Europe/Berlin:20231124T163000 DTEND;TZID=Europe/Berlin:20231124T180000 DTSTAMP:20260527T090436Z UID:0000001882@events.thp.uni-koeln.de DESCRIPTION:Henning Schomerus\, Lancaster University\n\nPhysical response of non-Hermitian topological systems\n\nIn photonic systems\, gain and los s can be used to induce intriguing effects that are linked to non-Hermitia n and topological physics. Prominent examples are exceptional points and t he non-Hermitian skin effect\, which can be used for enhanced sensing and directed amplification\, as well as symmetry-protected states\, which can be addressed by topological mode selection. Many of these applications mak e explicit use of mode nonorthogonality\, which becomes especially interes ting when the system is nonreciprocal. I describe how these effects can be probed in response theory\, transport\, and scattering\, and highlight fu ndamental practical limits of the observability of some effects.\n\nContac t Person: Sebastian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Alessandro Romito DTSTART;TZID=Europe/Berlin:20231208T163000 DTEND;TZID=Europe/Berlin:20231208T180000 DTSTAMP:20260527T090436Z UID:0000001892@events.thp.uni-koeln.de DESCRIPTION:Alessandro Romito\, Lancaster University\n\nMeasurement-induce d dynamics from single to many quantum trajectories\n\nWhen measured\, a q uantum system is subject to an unavoidable back-action\, which makes the s ystem evolve along stochastic quantum trajectories. Combined with unitary dynamics\, this can lead to localization effects\, like the quantum Zeno e ffect\, and to the stabilization of new out-of-equilibrium steady-state in many-body systems. The recent characterization of these phases has shown that the universal properties of their phase transitions differ between in dividual quantum trajectories and their statistical ensemble.\n\nIn this t alk\, I will review the description of quantum measurements and their back action in their discrete and continuous framework. I will first revisit t he Zeno effect along individual (post-selected) trajectories and their sta tistical ensemble in an exactly solved single-qubit model. I will then ext end the considerations to many-body systems and their measurement-induced phase transitions (MiPTs) and introduce a theory of partial post-selection \, in which we restrict the stochastic dynamics to a controllable subset o f quantum trajectories. Focusing on a Gaussian Majorana fermions model\, I will show that the MiPT universality of the post-selected (single-traject ory) dynamics is stable against the inclusion of stochasticity from a smal l subset of quantum trajectories\, but the monitored limit belongs to a di fferent universality class. Our results provide a systematic way to study trajectory-averaged measurement-induced effects.\n\nContact Person: Michae l Buchhold LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Sean Hartnoll DTSTART;TZID=Europe/Berlin:20231215T163000 DTEND;TZID=Europe/Berlin:20231215T180000 DTSTAMP:20260527T090436Z UID:0000001855@events.thp.uni-koeln.de DESCRIPTION:Sean Hartnoll\, Cambridge University\n\nArithmetic Quantum Cha os and Black Holes\n\nHyperbolic billiard motion is the canonical example of classical and quantum chaos. However\, if the billiard domain has certa in arithmetic properties\, the resulting quantum chaos is quite different and exhibits features that are more typical of integrable systems. I will review some of these features\, which have connections to deep concepts fr om number theory. I will then explain how such arithmetic quantum chaotic systems arise naturally inside black holes\, as the interior singularity i s approached.\n\nContact Person: Alexander Altland LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Thomas Guhr DTSTART;TZID=Europe/Berlin:20240112T163000 DTEND;TZID=Europe/Berlin:20240112T180000 DTSTAMP:20260527T090436Z UID:0000001866@events.thp.uni-koeln.de DESCRIPTION:Thomas Guhr\, Universität Duisburg-Essen\n\nDo the Stock Mark ets have a Memory?\n\n\n\nContact Person: not specified LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Jacopo De Nardis DTSTART;TZID=Europe/Berlin:20240119T163000 DTEND;TZID=Europe/Berlin:20240119T180000 DTSTAMP:20260527T090436Z UID:0000001910@events.thp.uni-koeln.de DESCRIPTION:Jacopo De Nardis\, Cergy Paris University\n\nExploring non-equ ilibrium many-body dynamics within the framework of generalized hydrodynam ics\n\nI will review the recent findings in the dynamics of one dimensiona l fluids close to integrability\, which are described at large scale by a generalised form of hydrodynamics. \nIn particular\, I will present the em ergence of anomalous super-diffusive transport in spin chains\, the fall a nd rise of hydrodynamics due to turbulence effects and the interplay of hy drodynamics and quantum fluctuations.\n\nContact Person: Silvia Pappalardi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Matteo Ippoliti DTSTART;TZID=Europe/Berlin:20240503T163000 DTEND;TZID=Europe/Berlin:20240503T180000 DTSTAMP:20260527T090436Z UID:0000001942@events.thp.uni-koeln.de DESCRIPTION:Matteo Ippoliti\, University of Texas at Austin\n\nRandomness\ , Entanglement\, and Thermal Equilibrium in the Quantum World\n\nHow does thermodynamic equilibrium emerge from the reversible\, coherent dynamics o f quantum many-body systems? This question underpins statistical mechanics \, and has been a subject of intense theoretical study for decades. Today\ , programmable quantum simulators and computers offer new ways to address this question experimentally\, prompting the development of novel theoreti cal frameworks. In this Colloquium I will give an overview of two recent d evelopments in this direction. The first is 'deep thermalization'\, which describes the emergence of maximally-random wavefunction distributions on a subsystem from projectively measuring the rest of the system--a stronger condition than conventional thermalization\, with the potential for usefu l applications in quantum computing. The second\, termed 'pseudothermaliza tion'\, builds on recent ideas from quantum cryptography. It describes a c lass of non-thermal states that have very limited quantum entanglement\, b ut are indistinguishable from highly-entangled thermal states to any obser ver with limited resources. These results highlight the subtle roles of ra ndomness\, entanglement\, and the observer's resources in characterizing t hermal equilibrium in programmable quantum matter.\n\nContact Person: Xhek Turkeshi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Guo-Yi Zhu DTSTART;TZID=Europe/Berlin:20240517T163000 DTEND;TZID=Europe/Berlin:20240517T180000 DTSTAMP:20260527T090436Z UID:0000001967@events.thp.uni-koeln.de DESCRIPTION:Guo-Yi Zhu\, University of Cologne\n\nMeasurement induced tran sitions of long-range entangled states\n\nMeasurement is an essential ingr edient for teleportation\, which can be harnessed to prepare long-range en tangled many-body states. In this colloquium\, I will give an overview ove r the measurement-induced quantum phase transitions for these long-range e ntangled states\, including the GHZ-like Nishimori’s cat\, topological s urface code\, and Majorana spin liquid.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Martin Zirnbauer DTSTART;TZID=Europe/Berlin:20240531T163000 DTEND;TZID=Europe/Berlin:20240531T180000 DTSTAMP:20260527T090436Z UID:0000001966@events.thp.uni-koeln.de DESCRIPTION:Martin Zirnbauer\, University of Cologne\n\nA Tale of Two Sigm a Models\n\nHow can non-Abelian fields avoid the fate of mass generation i n two dimensions\, where the Goldstone mechanism does not take effect? Mot ivated by this old question\, we tell the tale of two 2D nonlinear sigma m odels at topological angle equal to pi: the O(3) model as an effective fie ld theory of critical antiferromagnetic quantum spin chains and the Pruisk en model for the integer quantum Hall transition. We argue that both model s are infrared massless by a mechanism not appreciated so far in the liter ature.\n\nContact Person: Simon Trebst LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Rose Jordan\, Katharina Gross\, Sebastian Diehl DTSTART;TZID=Europe/Berlin:20240614T163000 DTEND;TZID=Europe/Berlin:20240614T180000 DTSTAMP:20260527T090436Z UID:0000001914@events.thp.uni-koeln.de DESCRIPTION:Rose Jordan\, Katharina Gross\, Sebastian Diehl\, University o f Cologne\, Scuola Normale Superiore and ISUE\n\nTonielli Award 2024\n\n\n \nContact Person: Sebastian Diehl LOCATION:Aula II University main building END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Sarang Gopalakrishnan DTSTART;TZID=Europe/Berlin:20240621T163000 DTEND;TZID=Europe/Berlin:20240621T180000 DTSTAMP:20260527T090436Z UID:0000001945@events.thp.uni-koeln.de DESCRIPTION:Sarang Gopalakrishnan\, Princeton University\n\nDiffusion with anomalous fluctuations\n\nWe discuss the dynamics of large-scale fluctuat ions in diffusive systems\, focusing on the full counting statistics (FCS) of charge transferred across a bipartition in a quasi-one-dimensional geo metry. We find at least two qualitatively different types of behavior. In the "standard" case -- corresponding to systems with no long-lived ballist ic modes -- the charge transfer distribution becomes asymptotically gaussi an at late times. In systems where diffusion coexists with ballistic modes \, such as the Dirac fluid in charge-neutral graphene and other two-compon ent plasmas\, the distribution instead achieves a nongaussian limit shape at late times. We provide a semi-analytic understanding of these limit sha pes\, as well as numerical evidence from simulating classical fluids.\n\nC ontact Person: Silvia Pappalardi LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Benjamin Beri DTSTART;TZID=Europe/Berlin:20240628T163000 DTEND;TZID=Europe/Berlin:20240628T180000 DTSTAMP:20260527T090436Z UID:0000001929@events.thp.uni-koeln.de DESCRIPTION:Benjamin Beri\, University of Cambridge\n\nTime crystals via t opological order\n\nI will discuss topologically ordered time crystals\, a dynamical phase of matter that uses topological order as the underlying f abric for time crystallinity. Time permitting\, I will briefly also mentio n results on how a holographic perspective\, naturally emerging from topol ogical time crystals\, can enrich our understanding of time crystallinity in "ordinary" 1D Floquet systems. Both topological time crystals and the n ew results on 1D Floquet systems may be amenable to realization on program mable quantum processors. The talk will be based on 2105.09694 and 2312.17 176 and may also mention 2401.04333\, a recent experiment on some aspects of topologically ordered time crystals.\n\nContact Person: Alex Altland LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Roderich Tumulka DTSTART;TZID=Europe/Berlin:20240705T163000 DTEND;TZID=Europe/Berlin:20240705T180000 DTSTAMP:20260527T090436Z UID:0000001975@events.thp.uni-koeln.de DESCRIPTION:Roderich Tumulka\, Tübingen\n\nOn the Present Status of Quant um Mechanics\n\nI have borrowed the title from the 1935 paper in which Sch rödinger introduced his cat example. I will explain why present-day criti cs still\, like Schrödinger\, see problems with the orthodox Copenhagen i nterpretation of quantum mechanics\, and what the alternatives are. I will also discuss whether these alternatives are compatible with relativity. F urthermore\, there are provable results about such alternatives\, and I wi ll describe some from recent years\, including some of my own.\n\nContact Person: David Gross LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Sebastian Steinhaus DTSTART;TZID=Europe/Berlin:20240712T163000 DTEND;TZID=Europe/Berlin:20240712T180000 DTSTAMP:20260527T090436Z UID:0000001984@events.thp.uni-koeln.de DESCRIPTION:Sebastian Steinhaus\, Friedrich-Schiller University Jena\n\nBu ilding quantum space-time with spin foams\n\nSpin foam quantum gravity is a non-perturbative\, background independent approach to quantizing gravity . It formulates a path integral as a sum over quantum geometries encoded i n group theoretic data as in loop quantum gravity\; thus it is frequently seen as a way of defining a covariant dynamics for this theory. \n\nIn thi s talk\, I want to motivate quantum gravity as a manifestly background ind ependent theory and define the gravitational path integral à la spin foam s. As a regularisation\, I introduce a triangulation and discuss how gravi ty can be formulated in the discrete\, via Regge calculus in a piece-wise flat way. Then I discuss how quantum geometry is encoded in a spin foam an d how it connects to Regge calculus in a putative semi-classical limit. I will review outstanding research challenges\, in particular for the Lorent zian theory\, and discuss concretely the construction of a cosmological mo del coupled to a scalar field.\n\nContact Person: Nele Callebaut LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Hans-Arwed Weidenmüller DTSTART;TZID=Europe/Berlin:20240718T173000 DTEND;TZID=Europe/Berlin:20240718T183000 DTSTAMP:20260527T090436Z UID:0000002012@events.thp.uni-koeln.de DESCRIPTION:Hans-Arwed Weidenmüller\, MPI Heidelberg\n\nThe rise of proba bility in physics — a personal view\n\nLater than in other fields of sci ence but eventually even more strongly probability has come to play a domi nant role in physical theories. Starting with the\nmiddle of the nineteent h century in classical physics\, it now dominates classical and quantum st atistics\, quantum theory\, classical chaos\, and random-matrix theory. I follow the lines of the historical development and show how in all cases p robability forced itself upon the physicists of the time\, often against t heir will.\n\nContact Person: Sebastian Diehl LOCATION:Seminar Room 0.03\, ETP END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Lorenzo Piroli DTSTART;TZID=Europe/Berlin:20241213T163000 DTEND;TZID=Europe/Berlin:20241213T174500 DTSTAMP:20260527T090436Z UID:0000002054@events.thp.uni-koeln.de DESCRIPTION:Lorenzo Piroli\, University of Bologna\n\nPreparing and measur ing many-body quantum states in digital devices\n\nQuantum-state preparati on and measurement protocols are well established branches of quantum info rmation and computation theory\, with immediate implications for quantum s imulation. While several existing algorithms rely on the assumption of dis posing of a perfect quantum computer\, current noisy intermediate-scale qu antum (NISQ) devices are limited in the number of qubits and the coherence time. Therefore\, simulating many-body physics poses the challenge of dev ising preparation and measurement schemes characterised by short "running time". In this talk\, I will present recent ideas to address this challeng e. In the first part of the talk\, I will discuss how traditional quantum- state preparation algorithms\, based on unitary quantum circuits\, can be improved making use of additional ancillas\, measurements\, and feedforwar d operations. Notably\, I will show examples where topologically ordered a nd long-range entangled states can be prepared in a time independent of th e system size. In the second part of the talk\, I will focus on measuremen t protocols to estimate quantum entanglement of many-body states. While th is is a notoriously difficult task\, typically requiring a number of measu rements or classical postprocessing resources growing exponentially in the system size\, I will show that efficient estimation strategies exist unde r some physically motivated assumptions on the state to be measured. Speci fically\, under the conditions that all the spatial correlation lengths ar e finite\, I will show that the entanglement can be detected and measured from polynomially-many local measurements. I will argue that some of the i deas and methods discussed could be of practical interest for implementati on in today’s quantum platforms.\n\nContact Person: Xhek Turkeshi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Andrea De Luca DTSTART;TZID=Europe/Berlin:20250110T163000 DTEND;TZID=Europe/Berlin:20250110T174500 DTSTAMP:20260527T090436Z UID:0000002079@events.thp.uni-koeln.de DESCRIPTION:Andrea De Luca\, Cergy Paris University\n\nUniversal aspects o f many-body quantum dynamics\n\nI will present a summary of recent develop ments in understanding quantum dynamics in out-of-equilibrium many-body sy stems. After revisiting the concept of thermalization\, I will discuss the fundamental assumptions to justify its occurrence in generic systems\, ex plaining the typicality assumptions that give rise to the connection with random matrices and the eigenstate thermalization hypothesis. I will then move to more recent developments in this context based on the introduction of tractable classes of models\, called random unitary circuits. I will s how how some features of chaotic quantum systems can be explained by this approach\, such as the production of entanglement. In addition\, I will hi ghlight new universality mechanisms that emerge precisely for spatially ex tended systems\, giving rise to a specific notion of many-body quantum cha os.\n\nContact Person: Silvia Pappalardi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Anushya Chandran DTSTART;TZID=Europe/Berlin:20250117T163000 DTEND;TZID=Europe/Berlin:20250117T174500 DTSTAMP:20260527T090436Z UID:0000002047@events.thp.uni-koeln.de DESCRIPTION:Anushya Chandran\, Boston University\n\nNon-reciprocity in nea r-term quantum platforms\n\nReciprocity relates cause and effect at two po ints in a system. In a reciprocal system\, a disturbance at A is felt at B with the same intensity as a disturbance at B would be felt at A. Somewha t surprisingly\, this innocuous relation has far-reaching consequences: fo r example\, relations between transport coefficients. Breaking reciprocity breaks these relations and opens up a world of new steady-state behaviors \, such as macroscopic oscillations and persistent currents. Controlling n on-reciprocal effects provides a short-term goal for quantum simulators in which non-reciprocity can be readily achieved using drives and dissipatio n\, and an intriguing route to engineering devices\, such as circulators a nd isolators\, needed for future quantum technologies.\n\nI will describe how to use non-reciprocal responses of band structures to achieve useful n on-reciprocal effects in qubit-cavity platforms. We will obtain topologica l photon pumps\, topologically protected circulating photons and ways to ‘boost’ non-classical cavity states to larger photon number. I will co nclude with a status update on ongoing experimental efforts based on our a pproach in superconducting circuits.\n\nContact Person: Silvia Pappalardi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Robert Raussendorf DTSTART;TZID=Europe/Berlin:20250124T163000 DTEND;TZID=Europe/Berlin:20250124T173000 DTSTAMP:20260527T090436Z UID:0000002051@events.thp.uni-koeln.de DESCRIPTION:Robert Raussendorf\, Hannover\n\nComputationally Universal Pha ses of Quantum Matter\n\nMeasurement based quantum computation is a scheme of universal quantum computation in which the computational process is dr iven by measurements alone [1]. No unitary evolution takes place. In fact\ , the measurements employed are all local\, and thus the computational pow er hinges on the initial quantum state—hence called the resource state.\ nSome resource states give universal computational power\, but most quantu m states in Hilbert space provide no computational power at all [2]. This picture changes in the presence of symmetry. Namely\, for phases of ground states of symmetric Hamiltonians\, i.e.\, symmetry-protected topological (SPT) phases\, it has been found that computational power is uniform acros s those phases. This observation gave rise to the term `computational phas es of quantum matter’ [3\,4]. In my talk\, I give a short history of thi s line of research\, and then present examples of symmetry protected quant um phases that have universal computational power [5 - 7].\n\nJoint work w ith: C. Okay\, D.-S. Wang\, D.T. Stephen\, J. Bermejo-Vega\, A. Prakash\, and H.P. Nautrup.\n\n[1] R. Raussendorf and H.J.Briegel\, Phys. Rev. Lett. 86\, 5188 (2001).\n[2] D. Gross\, S. T. Flammia\, and J. Eisert\, Phys. R ev. Lett. 102\, 190501 (2009).\n[3] A. C. Doherty and S. D. Bartlett\, Phy s. Rev. Lett. 103\, 020506 (2009).\n[4] A. Miyake\, Phys. Rev. Lett. 105\, 040501 (2010).\n[5] R. Raussendorf et al.\, Phys. Rev. Lett. 122\, 090501 (2019).\n[6] D.T. Stephen et al.\, Quantum 3\, 142 (2019).\n[7] A.K. Dani el\, R.N. Alexander\, A. Miyake\, Quantum 4\, 228 (2020).\n\nContact Perso n: David Gross / Simon Trebst LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Mark T. Mitchison DTSTART;TZID=Europe/Berlin:20250221T163000 DTEND;TZID=Europe/Berlin:20250221T183000 DTSTAMP:20260527T090436Z UID:0000002061@events.thp.uni-koeln.de DESCRIPTION:Mark T. Mitchison\, Trinity College Dublin\n\nDiagnosing chaos with projected ensembles of process tensors\n\nThe process tensor provide s a general representation of a quantum system evolving under repeated int erventions\, and is fundamental for numerical simulations of open quantum systems and local many-body dynamics. In this talk\, I will introduce the projected process ensemble\, an ensemble of pure output states of a proces s tensor in a given basis of local interventions\, and use it to define in creasingly more fine-grained probes of quantum chaos. The first moment of this ensemble encapsulates numerous previously studied chaos quantifiers\, including the Alicki-Fannes quantum dynamical entropy\, butterfly flutter fidelity\, and spatiotemporal entanglement. I will show that entanglement structures within the ensemble's higher moments can sharply distinguish c haotic from integrable dynamics\, overcoming deficiencies of the quantum d ynamical and spatiotemporal entropies. These conclusions are supported by extensive numerical simulations of many-body dynamics for a range of spin- chain models\, including non-interacting\, interacting-integrable\, chaoti c\, and many-body localized regimes. Our results elucidate the fingerprint s of chaos on spatiotemporal correlations in quantum stochastic processes\ , and provide a unified framework for analyzing the complexity of unitary and monitored many-body dynamics.\n\nContact Person: Silvia Pappalardi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Zohar Nussinov DTSTART;TZID=Europe/Berlin:20250411T163000 DTEND;TZID=Europe/Berlin:20250411T174500 DTSTAMP:20260527T090436Z UID:0000002084@events.thp.uni-koeln.de DESCRIPTION:Zohar Nussinov\, Washington University St. Louis\n\nGeneralize d Symmetries\, Dualities\, Topological Orders\, and Topological Quantum Fi eld Theories\n\nWe introduce and discuss aspects of “d-dimensional gauge -like symmetries” (these encompass both generalized "higher form" and "s ubsystem" symmetries). We show how such symmetries relate to dimensional r eductions. In particular\, we discuss the effects of thermal fluctuations using a generalization of Elitzur’s theorem. We describe how these symme tries may lead to topological orders and illustrate that\, depending on th e system geometry\, there are both quantum and classical systems that have degeneracies that may depend on the system topology or have an entropy th at is holographic with a degeneracy that is exponentially large in the bou ndary area of the system. We will outline the “bond algebraic” approac h to dualities and explain why dualities are often conformal. Using this a pproach\, we illustrate that the nearest neighbor “XXZ honeycomb compass ” and square lattice Majorana Hubbard model both exhibit exact 3D Ising type transitions. With these dualities\, we compute the free energies of t he so-called fracton "X-cube model" and other topologically ordered syste ms. We will introduce topologically ordered theories that do not readily a dmit\na TQFT description.\n\nContact Person: Simon Trebst LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Rosario Fazio DTSTART;TZID=Europe/Berlin:20250425T163000 DTEND;TZID=Europe/Berlin:20250425T173000 DTSTAMP:20260527T090436Z UID:0000002049@events.thp.uni-koeln.de DESCRIPTION:Rosario Fazio\, ICTP and University of Naples\n\nDissipative t ime crystals\n\n\n\nContact Person: Silvia Pappalardi LOCATION:0.01 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Romain Vasseur DTSTART;TZID=Europe/Berlin:20250502T163000 DTEND;TZID=Europe/Berlin:20250502T174500 DTSTAMP:20260527T090436Z UID:0000002094@events.thp.uni-koeln.de DESCRIPTION:Romain Vasseur\, Geneva\n\nLearnability phase transitions in m onitored quantum systems\n\nWhile many-body quantum physics has traditiona lly focused on the properties of cold matter in thermal equilibrium\, emer ging noisy intermediate-scale quantum (NISQ) platforms allow access to far -from-equilibrium dynamics with local space and time control over interact ions. In this new era of “interactive quantum dynamics”\, a key challe nge is to identify universal features of non-equilibrium quantum dynamics\ , transport\, and many-body entanglement. In this talk\, I will discuss ne w types of non-equilibrium quantum phases of matter and phase transitions\ , with an emphasis on emergent classical statistical mechanics description s of quantum entanglement dynamics. In particular\, I will focus on the re cently discovered “learnability phase transitions” that occur in monit ored quantum systems and separate phases characterized by the amount of qu antum information that can be extracted from measurements.\n\nContact Pers on: Simon Trebst LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Alioscia Hamma DTSTART;TZID=Europe/Berlin:20250509T163000 DTEND;TZID=Europe/Berlin:20250509T174500 DTSTAMP:20260527T090436Z UID:0000002107@events.thp.uni-koeln.de DESCRIPTION:Alioscia Hamma\, University of Naples Federico II\n\nWhat is m agic and why do we care?\n\nIn recent years\, the notion of magic in quant um physics - originally confined to more esoteric quantum information proc essing subfields - has attracted the attention of the community of quantum many-body physics\, quantum chaos and complexity\, high-energy physics\, AdS-CFT and the foundations of quantum mechanics. In this colloquium\, I w ill give a survey of what quantum magic is\, how it can be measured\, and why we should care (and why and when we should not).\n\nContact Person: Xh ek Turkeshi LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Jonas Haferkamp DTSTART;TZID=Europe/Berlin:20250523T163000 DTEND;TZID=Europe/Berlin:20250523T174500 DTSTAMP:20260527T090436Z UID:0000002151@events.thp.uni-koeln.de DESCRIPTION:Jonas Haferkamp\, Saarland University\n\nRandom unitaries in e xtremely low depth\n\nRandom unitaries are a central tool in quantum infor mation theory\, with applications ranging from encoding and decoding quant um information to modeling black-hole dynamics. In this talk\, we will rev iew recent advances in the generation of random unitaries in extremely low depth. More precisely\, we will discuss how to generate so called pseudor andom unitaries and k-designs with circuits of almost logarithmic depth. W e will explain how this remarkably fast scrambling of information in quant um circuits raises questions about the limits of measuring fundamental pro perties of quantum states and directly enhances quantum learning primitive s such as classical shadows.\n\nContact Person: Markus Heinrich LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Jad Halimeh DTSTART;TZID=Europe/Berlin:20250711T163000 DTEND;TZID=Europe/Berlin:20250711T174500 DTSTAMP:20260527T090436Z UID:0000002112@events.thp.uni-koeln.de DESCRIPTION:Jad Halimeh\, LMU Munich\n\nQuantum simulation of far-from-equ ilibrium dynamics of gauge theories\n\nI will go over my research profile\ , which bridges quantum many-body physics and quantum simulation through t wo main pillars. The first focuses on investigating exotic far-from-equili brium phenomena in lattice gauge theories\, uncovering properties of dynam ical phase transitions and criticality\, as well as various nonergodic reg imes. The second aims to develop experimentally feasible schemes to probe such dynamics on state-of-the-art quantum hardware\, including cold atoms and molecules\, superconducting qubits\, and trapped ions. We will go over a series of experiments\, which we led on the theory side\, highlighting the interplay between these two pillars. We will provide an overview of ou r plans to advance these experiments to probe gauge-theory dynamics in hig her spatial dimensions and in the quantum-field-theory limit.\n\nContact P erson: Simon Trebst LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Tom O'Brien DTSTART;TZID=Europe/Berlin:20251014T160000 DTEND;TZID=Europe/Berlin:20251014T173000 DTSTAMP:20260527T090436Z UID:0000002236@events.thp.uni-koeln.de DESCRIPTION:Tom O'Brien\, Google Quantum AI\n\nWhat defines progress in ne ar-term quantum computing?\n\nRecent advances in experimental quantum devi ces have pushed the boundary of quantum advantage claims beyond sampling t asks[1]\, a critical step towards all known quantum computing applications . As we progress into early fault-tolerance[2] in the next five years\, qu estions of which applications remain feasible for quantum computers\, what new algorithms and applications remain to be found\, and how can the fiel d best focus its efforts towards quantum benefit\, remain open and intrigu ing. In this talk I will cover recent advances from Quantum AI in this are a [1\,2\,3\,4]\, and detail the areas we think are the most in need of att ention from the quantum community.\n\n[1] https://arxiv.org/abs/2506.10191 \n[2] https://www.nature.com/articles/s41586-024-08449-y \n[3] https://arx iv.org/abs/2407.21775\n[4] https://arxiv.org/abs/2408.08292\n\nContact Per son: Simon Trebst LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Nat Tantivasadakarn DTSTART;TZID=Europe/Berlin:20251107T163000 DTEND;TZID=Europe/Berlin:20251107T180000 DTSTAMP:20260527T090436Z UID:0000002263@events.thp.uni-koeln.de DESCRIPTION:Nat Tantivasadakarn\, Stony Brook\n\nFrom dualities to non-inv ertible symmetries: a tensor network perspective\n\nDualities have long se rved as a powerful lens for understanding the structure of quantum many-bo dy systems. In this talk\, I will explore how the concept of duality has r ecently led to new insights into non-invertible symmetries --- a generaliz ed notion of symmetry that goes beyond the familiar group framework. Focus ing on one-dimensional spin chains\, I will revisit the Kramers–Wannier duality of the transverse-field Ising model\, its modern interpretation as a non-invertible symmetry\, and then describe a broader construction that reveals new kinds of symmetry-protected topological phases and self-duali ty transformations. Throughout\, I will emphasize how tensor networks prov ide a unifying and intuitive framework for visualizing and realizing these ideas on the lattice.\n\nContact Person: Simon Trebst LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Karol Życzkowski DTSTART;TZID=Europe/Berlin:20260116T163000 DTEND;TZID=Europe/Berlin:20260116T174500 DTSTAMP:20260527T090436Z UID:0000002259@events.thp.uni-koeln.de DESCRIPTION:Karol Życzkowski\, CFT PAN (Warsaw) & IFT UJ (Cracow)\n\n100 Years Later: Exploring Typical and Atypical Quantum Structures\n\nModern quantum mechanics is already 100 years old and we became accustomed to the observation that it accurately describes phenomena at the microscale. Rat her than questioning whether quantum theory is good enough one often asks which structures allowed by quantum mechanics can be useful for some pract ical purposes. In this talk we will analyze various quantum structures\, i ncluding the set of mixed quantum states of a finite order\, along with qu antum operations and quantum measurements which act upon them. We search f or atypical quantum objects with extreme properties and identify some exem plary highly entangled multipartite states and strongly entangling quantum gates\, which can be applied for quantum information processing. Addition ally\, we will examine discrete structures within the Hilbert space\, incl uding quantum designs: collections of objects\, chosen in such a way that the average over them approximates the average over the measure analyzed f or all functions of a given degree.\n\nContact Person: David Gross LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Seung-Sup B. Lee DTSTART;TZID=Europe/Berlin:20260130T163000 DTEND;TZID=Europe/Berlin:20260130T174500 DTSTAMP:20260527T090436Z UID:0000002234@events.thp.uni-koeln.de DESCRIPTION:Seung-Sup B. Lee\, Seoul National University\n\nHundness in tw isted bilayer graphene and hardness in random quantum circuits\n\nIn this talk\, we explore two distinct frontiers of many-body physics where sophis ticated numerical methods reveal the nature of quantum phases and the boun dary of classical hardness. In the first topic\, we investigate magic-angl e twisted bilayer graphene (MATBG) using dynamical mean-field theory (DMFT ) with the numerical renormalization group (NRG) impurity solver. We find that effective Hund interactions\, induced by the nonretarded electron-pho non coupling\, play a crucial role in causing a robust pseudogap\, quantum criticality\, and enhancement of pairing susceptibility near filling ±2. In the second topic\, we discuss two-dimensional tensor network studies o n random quantum circuits on square lattices\, where classical complexity changes drastically depending on the gate type.\n\nContact Person: Fabian Kugler LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Soo-Jong Rey DTSTART;TZID=Europe/Berlin:20260410T163000 DTEND;TZID=Europe/Berlin:20260410T174500 DTSTAMP:20260527T090436Z UID:0000002367@events.thp.uni-koeln.de DESCRIPTION:Soo-Jong Rey\, Kwangwoon University\, Korea\n\nInfrared Diverg ence Cancellation in QED as Trace Preservation of a Quantum Channel\n\nI r ecast the cancellation of infrared(IR) divergences in QED\nusing the Schwi nger-Keldysh closed time path formalism and the framework of\nopen quantum systems. Treating soft radiation photons as the environment\, I\nshow tha t IR cancellation is trace preservation of the resulting quantum\nchannel — unitarity of the open system inherited from the full theory. The\nSuda kov form factor is the exclusive Kraus operator norm\, and the\nNakajima-Z wanzig master equation with an Ohmic memory kernel provides a\ndynamical r eformulation of the Sudakov resummation. We extend the framework\nto QED i n 1+1 dimensions\, where the absence of propagating photons and the\nchira l anomaly produce a novel non-Markovian universality class at\nradiation t hreshold. I connect this naturally to Fermi edge singularities\nin condens ed matter\, where similar structure appears.\n\nContact Person: Sebastian Diehl LOCATION:0.01 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Flore Kunst DTSTART;TZID=Europe/Berlin:20260522T163000 DTEND;TZID=Europe/Berlin:20260522T173000 DTSTAMP:20260527T090436Z UID:0000002053@events.thp.uni-koeln.de DESCRIPTION:Flore Kunst\, Max Planck Institute for the Science of Light\n\ nExceptional non-Hermitian topology\n\nWhile most theoretical research foc usses on studying systems isolated from their surroundings\, we take a mor e realistic perspective by taking environmental effects such as gain and l oss of particles explicitly into account. As a consequence\, we arrive at so-called non-Hermitian descriptions. This approach is highly relevant to quantum optics\, electronics\, mechanical metamaterials\, nonconservative biological systems as well as quantum systems\, to name a few. In recent y ears\, non-Hermiticity has been investigated in the context of topology\, which is a branch of mathematics describing properties that can only chang e step-wise and which has found many applications in physics. Adding the i ngredients of non-Hermitian approaches and topology together has revealed a dramatic enrichment of the phenomenology of topological phases and resul ted in a new\, rapidly expanding cross-disciplinary research field. In thi s talk\, I will provide an overview of the field focussing on fundamental aspects\, experimental realizations and I will briefly touch on applicatio ns.\n\nContact Person: Simon Trebst LOCATION:0.03 END:VEVENT BEGIN:VEVENT SUMMARY:TPK | Lukasz Fidkowski DTSTART;TZID=Europe/Berlin:20260619T163000 DTEND;TZID=Europe/Berlin:20260619T174500 DTSTAMP:20260527T090436Z UID:0000002378@events.thp.uni-koeln.de DESCRIPTION:Lukasz Fidkowski\, UW Seattle\n\nTo be announced\n\n\n\nContac t Person: Simon Trebst LOCATION:0.03 END:VEVENT END:VCALENDAR