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PRODID:Institute for Theoretical Physics - Events
X-WR-CALDESC:TPK
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X-WR-TIMEZONE:Europe/Berlin
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. Bernd Rosenow
DTSTART;VALUE=DATE-TIME:20101119T164500
DTEND;VALUE=DATE-TIME:20101119T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminar Room ITP
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. B. Trauzettel
DTSTART;VALUE=DATE-TIME:20101126T163000
DTEND;VALUE=DATE-TIME:20101126T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminar Room ITP
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. Karyn Le Hur
DTSTART;VALUE=DATE-TIME:20101210T164500
DTEND;VALUE=DATE-TIME:20101210T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminar Room ITP
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Matthias Sperl
DTSTART;VALUE=DATE-TIME:20110204T163000
DTEND;VALUE=DATE-TIME:20110204T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Nick Manton
DTSTART;VALUE=DATE-TIME:20110408T163000
DTEND;VALUE=DATE-TIME:20110408T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Arne Traulsen
DTSTART;VALUE=DATE-TIME:20110415T163000
DTEND;VALUE=DATE-TIME:20110415T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Klaus Hornberger
DTSTART;VALUE=DATE-TIME:20110429T163000
DTEND;VALUE=DATE-TIME:20110429T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Andrew Mitchell
DTSTART;VALUE=DATE-TIME:20110506T163000
DTEND;VALUE=DATE-TIME:20110506T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Ganna Rozhnova
DTSTART;VALUE=DATE-TIME:20110513T163000
DTEND;VALUE=DATE-TIME:20110513T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. D. Vollhardt
DTSTART;VALUE=DATE-TIME:20110520T163000
DTEND;VALUE=DATE-TIME:20110520T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminar Room ITP
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Armin Bunde
DTSTART;VALUE=DATE-TIME:20110527T163000
DTEND;VALUE=DATE-TIME:20110527T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Royce K.P. Zia
DTSTART;VALUE=DATE-TIME:20110610T163000
DTEND;VALUE=DATE-TIME:20110610T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr Tim Newman
DTSTART;VALUE=DATE-TIME:20110624T163000
DTEND;VALUE=DATE-TIME:20110624T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminar Room ITP
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. A. Altland
DTSTART;VALUE=DATE-TIME:20110715T163000
DTEND;VALUE=DATE-TIME:20110715T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Erik Aurell
DTSTART;VALUE=DATE-TIME:20111014T143000
DTEND;VALUE=DATE-TIME:20111014T153000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Jonas Larson
DTSTART;VALUE=DATE-TIME:20111021T163000
DTEND;VALUE=DATE-TIME:20111021T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Günter Radons
DTSTART;VALUE=DATE-TIME:20111104T163000
DTEND;VALUE=DATE-TIME:20111104T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Armin Bunde
DTSTART;VALUE=DATE-TIME:20111118T163000
DTEND;VALUE=DATE-TIME:20111118T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Gregory Schehr
DTSTART;VALUE=DATE-TIME:20111202T163000
DTEND;VALUE=DATE-TIME:20111202T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Dmitri Diakonov
DTSTART;VALUE=DATE-TIME:20111209T163000
DTEND;VALUE=DATE-TIME:20111209T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. Milena Grifoni
DTSTART;VALUE=DATE-TIME:20111216T163000
DTEND;VALUE=DATE-TIME:20111216T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. J. Schmalian
DTSTART;VALUE=DATE-TIME:20120113T163000
DTEND;VALUE=DATE-TIME:20120113T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Simon Trebst
DTSTART;VALUE=DATE-TIME:20120120T163000
DTEND;VALUE=DATE-TIME:20120120T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. Hildegard Meyer-Ortmanns
DTSTART;VALUE=DATE-TIME:20120127T163000
DTEND;VALUE=DATE-TIME:20120127T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Alexander Ludwig
DTSTART;VALUE=DATE-TIME:20120203T163000
DTEND;VALUE=DATE-TIME:20120203T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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 effects
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Boris Gutkin
DTSTART;VALUE=DATE-TIME:20120413T163000
DTEND;VALUE=DATE-TIME:20120413T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Alexander Altland
DTSTART;VALUE=DATE-TIME:20120420T163000
DTEND;VALUE=DATE-TIME:20120420T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Wojciech De Roeck
DTSTART;VALUE=DATE-TIME:20120427T163000
DTEND;VALUE=DATE-TIME:20120427T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Mark Oliver Goerbig
DTSTART;VALUE=DATE-TIME:20120504T163000
DTEND;VALUE=DATE-TIME:20120504T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Kirill Shtengel
DTSTART;VALUE=DATE-TIME:20120511T163000
DTEND;VALUE=DATE-TIME:20120511T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Sabine Lennartz
DTSTART;VALUE=DATE-TIME:20120518T163000
DTEND;VALUE=DATE-TIME:20120518T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. I. Müller
DTSTART;VALUE=DATE-TIME:20120525T163000
DTEND;VALUE=DATE-TIME:20120525T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Subir Sachdev
DTSTART;VALUE=DATE-TIME:20120608T163000
DTEND;VALUE=DATE-TIME:20120608T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. Heiko Rieger
DTSTART;VALUE=DATE-TIME:20120615T163000
DTEND;VALUE=DATE-TIME:20120615T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Pascal Simon
DTSTART;VALUE=DATE-TIME:20120706T163000
DTEND;VALUE=DATE-TIME:20120706T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Martin Evans
DTSTART;VALUE=DATE-TIME:20120713T163000
DTEND;VALUE=DATE-TIME:20120713T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Lars Fritz
DTSTART;VALUE=DATE-TIME:20121012T163000
DTEND;VALUE=DATE-TIME:20121012T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Dirk Witthaut
DTSTART;VALUE=DATE-TIME:20121102T163000
DTEND;VALUE=DATE-TIME:20121102T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Professor Steven H. Simon
DTSTART;VALUE=DATE-TIME:20121109T163000
DTEND;VALUE=DATE-TIME:20121109T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. K. Wolff
DTSTART;VALUE=DATE-TIME:20121116T163000
DTEND;VALUE=DATE-TIME:20121116T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Paolo Politi
DTSTART;VALUE=DATE-TIME:20121123T163000
DTEND;VALUE=DATE-TIME:20121123T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Mikhail A. Skvortsov
DTSTART;VALUE=DATE-TIME:20121130T163000
DTEND;VALUE=DATE-TIME:20121130T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. B. Rosenow
DTSTART;VALUE=DATE-TIME:20121207T160000
DTEND;VALUE=DATE-TIME:20121207T171500
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Silke Weinfurtner
DTSTART;VALUE=DATE-TIME:20121214T160000
DTEND;VALUE=DATE-TIME:20121214T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. Pasquale Calabrese
DTSTART;VALUE=DATE-TIME:20130111T160000
DTEND;VALUE=DATE-TIME:20130111T171500
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. Jan von Delft
DTSTART;VALUE=DATE-TIME:20130118T160000
DTEND;VALUE=DATE-TIME:20130118T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Johanna Erdmenger
DTSTART;VALUE=DATE-TIME:20130412T163000
DTEND;VALUE=DATE-TIME:20130412T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Stefan Scheel
DTSTART;VALUE=DATE-TIME:20130419T163000
DTEND;VALUE=DATE-TIME:20130419T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. F. Assaad
DTSTART;VALUE=DATE-TIME:20130426T163000
DTEND;VALUE=DATE-TIME:20130426T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Bartlomiej Waclaw
DTSTART;VALUE=DATE-TIME:20130503T163000
DTEND;VALUE=DATE-TIME:20130503T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. M. Troyer
DTSTART;VALUE=DATE-TIME:20130607T163000
DTEND;VALUE=DATE-TIME:20130607T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Debashish Chowdhury
DTSTART;VALUE=DATE-TIME:20130614T163000
DTEND;VALUE=DATE-TIME:20130614T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. Florian Marquardt
DTSTART;VALUE=DATE-TIME:20130621T163000
DTEND;VALUE=DATE-TIME:20130621T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Tobias Galla
DTSTART;VALUE=DATE-TIME:20130628T163000
DTEND;VALUE=DATE-TIME:20130628T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. Reinhold Egger
DTSTART;VALUE=DATE-TIME:20130705T163000
DTEND;VALUE=DATE-TIME:20130705T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. V. L. Pokrovsky
DTSTART;VALUE=DATE-TIME:20130719T163000
DTEND;VALUE=DATE-TIME:20130719T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Anatoly Konechny
DTSTART;VALUE=DATE-TIME:20131018T163000
DTEND;VALUE=DATE-TIME:20131018T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20131025T163000
DTEND;VALUE=DATE-TIME:20131025T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Peter Wölfle
DTSTART;VALUE=DATE-TIME:20131129T163000
DTEND;VALUE=DATE-TIME:20131129T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. Florian Marquardt
DTSTART;VALUE=DATE-TIME:20131206T163000
DTEND;VALUE=DATE-TIME:20131206T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Christian Maes
DTSTART;VALUE=DATE-TIME:20131213T163000
DTEND;VALUE=DATE-TIME:20131213T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Jacobus Verbaarschot
DTSTART;VALUE=DATE-TIME:20140110T163000
DTEND;VALUE=DATE-TIME:20140110T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Prof. Dr. Andreas Läuchli
DTSTART;VALUE=DATE-TIME:20140117T163000
DTEND;VALUE=DATE-TIME:20140117T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20140124T163000
DTEND;VALUE=DATE-TIME:20140124T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20140131T163000
DTEND;VALUE=DATE-TIME:20140131T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20140207T163000
DTEND;VALUE=DATE-TIME:20140207T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20140411T163000
DTEND;VALUE=DATE-TIME:20140411T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20140425T163000
DTEND;VALUE=DATE-TIME:20140425T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dr. Regine Frank
DTSTART;VALUE=DATE-TIME:20140509T163000
DTEND;VALUE=DATE-TIME:20140509T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20140516T163000
DTEND;VALUE=DATE-TIME:20140516T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Tim Wehling
DTSTART;VALUE=DATE-TIME:20140523T163000
DTEND;VALUE=DATE-TIME:20140523T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | David Gross
DTSTART;VALUE=DATE-TIME:20140606T160000
DTEND;VALUE=DATE-TIME:20140606T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Sebastian Diehl
DTSTART;VALUE=DATE-TIME:20140620T160000
DTEND;VALUE=DATE-TIME:20140620T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Jie Ren
DTSTART;VALUE=DATE-TIME:20140627T160000
DTEND;VALUE=DATE-TIME:20140627T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Maria Hermanns
DTSTART;VALUE=DATE-TIME:20140704T160000
DTEND;VALUE=DATE-TIME:20140704T170000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | U. Gerland
DTSTART;VALUE=DATE-TIME:20141107T163000
DTEND;VALUE=DATE-TIME:20141107T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | C. Kiefer
DTSTART;VALUE=DATE-TIME:20141114T163000
DTEND;VALUE=DATE-TIME:20141114T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | John Chalker
DTSTART;VALUE=DATE-TIME:20141204T160000
DTEND;VALUE=DATE-TIME:20141204T170000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20141205T163000
DTEND;VALUE=DATE-TIME:20141205T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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/
LOCATION:Seminarraum Theoretische Physik
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Byungnam Kahng
DTSTART;VALUE=DATE-TIME:20150109T163000
DTEND;VALUE=DATE-TIME:20150109T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminar Room TP 0.03
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Christopher Mudry
DTSTART;VALUE=DATE-TIME:20150116T163000
DTEND;VALUE=DATE-TIME:20150116T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:seminar room TP 0.03
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | M. Fleischhauer
DTSTART;VALUE=DATE-TIME:20150123T163000
DTEND;VALUE=DATE-TIME:20150123T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:seminar room TP 0.03
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | D. Schuricht
DTSTART;VALUE=DATE-TIME:20150130T163000
DTEND;VALUE=DATE-TIME:20150130T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:seminar room TP 0.03
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Su-Chan Park
DTSTART;VALUE=DATE-TIME:20150206T163000
DTEND;VALUE=DATE-TIME:20150206T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:Seminar Room TP 0.03
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Dmitry Fedosov
DTSTART;VALUE=DATE-TIME:20150410T163000
DTEND;VALUE=DATE-TIME:20150410T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20150417T163000
DTEND;VALUE=DATE-TIME:20150417T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20150424T163000
DTEND;VALUE=DATE-TIME:20150424T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminar Room TP 0.03
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Jens Bardason
DTSTART;VALUE=DATE-TIME:20150508T163000
DTEND;VALUE=DATE-TIME:20150508T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminar Room TP 0.03
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Tomaz Prosen
DTSTART;VALUE=DATE-TIME:20150515T163000
DTEND;VALUE=DATE-TIME:20150515T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20150522T163000
DTEND;VALUE=DATE-TIME:20150522T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20150612T163000
DTEND;VALUE=DATE-TIME:20150612T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20150619T163000
DTEND;VALUE=DATE-TIME:20150619T174500
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20150626T163000
DTEND;VALUE=DATE-TIME:20150626T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20150710T163000
DTEND;VALUE=DATE-TIME:20150710T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20150717T163000
DTEND;VALUE=DATE-TIME:20150717T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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?
LOCATION:TP seminar room 0.03
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Till Kranz
DTSTART;VALUE=DATE-TIME:20150828T140000
DTEND;VALUE=DATE-TIME:20150828T153000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20151023T163000
DTEND;VALUE=DATE-TIME:20151023T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:seminar room TP 0.03
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Pieter Rein ten Wolde
DTSTART;VALUE=DATE-TIME:20151030T163000
DTEND;VALUE=DATE-TIME:20151030T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20151106T163000
DTEND;VALUE=DATE-TIME:20151106T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20151127T163000
DTEND;VALUE=DATE-TIME:20151127T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20151204T163000
DTEND;VALUE=DATE-TIME:20151204T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:TP seminar room 0.03
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Sebastian Diehl
DTSTART;VALUE=DATE-TIME:20160108T163000
DTEND;VALUE=DATE-TIME:20160108T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:TP seminar room 0.03
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Erik Aurell
DTSTART;VALUE=DATE-TIME:20160115T163000
DTEND;VALUE=DATE-TIME:20160115T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20160212T163000
DTEND;VALUE=DATE-TIME:20160212T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20160226T163000
DTEND;VALUE=DATE-TIME:20160226T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20160408T140000
DTEND;VALUE=DATE-TIME:20160408T153000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20160415T163000
DTEND;VALUE=DATE-TIME:20160415T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20160513T163000
DTEND;VALUE=DATE-TIME:20160513T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20160603T163000
DTEND;VALUE=DATE-TIME:20160603T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20160610T163000
DTEND;VALUE=DATE-TIME:20160610T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20160617T163000
DTEND;VALUE=DATE-TIME:20160617T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20160701T163000
DTEND;VALUE=DATE-TIME:20160701T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20160715T163000
DTEND;VALUE=DATE-TIME:20160715T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20161021T163000
DTEND;VALUE=DATE-TIME:20161021T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20161111T163000
DTEND;VALUE=DATE-TIME:20161111T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20161118T163000
DTEND;VALUE=DATE-TIME:20161118T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:TP seminar room 0.03
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Walter Hofstetter
DTSTART;VALUE=DATE-TIME:20161125T163000
DTEND;VALUE=DATE-TIME:20161125T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20161216T163000
DTEND;VALUE=DATE-TIME:20161216T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:TP seminar room 0.03
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Malte Henkel
DTSTART;VALUE=DATE-TIME:20170113T163000
DTEND;VALUE=DATE-TIME:20170113T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20170120T163000
DTEND;VALUE=DATE-TIME:20170120T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20170127T163000
DTEND;VALUE=DATE-TIME:20170127T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20170203T163000
DTEND;VALUE=DATE-TIME:20170203T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20170512T163000
DTEND;VALUE=DATE-TIME:20170512T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20170519T163000
DTEND;VALUE=DATE-TIME:20170519T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20170526T163000
DTEND;VALUE=DATE-TIME:20170526T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20170602T163000
DTEND;VALUE=DATE-TIME:20170602T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20170623T163000
DTEND;VALUE=DATE-TIME:20170623T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20170627T160000
DTEND;VALUE=DATE-TIME:20170627T170000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20170630T163000
DTEND;VALUE=DATE-TIME:20170630T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20170707T163000
DTEND;VALUE=DATE-TIME:20170707T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20170714T163000
DTEND;VALUE=DATE-TIME:20170714T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20171020T163000
DTEND;VALUE=DATE-TIME:20171020T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
LOCATION:TP seminar room 0.03
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Zi Yang Meng
DTSTART;VALUE=DATE-TIME:20171110T163000
DTEND;VALUE=DATE-TIME:20171110T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20171117T163000
DTEND;VALUE=DATE-TIME:20171117T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20171124T163000
DTEND;VALUE=DATE-TIME:20171124T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20171201T163000
DTEND;VALUE=DATE-TIME:20171201T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20180112T163000
DTEND;VALUE=DATE-TIME:20180112T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20180119T163000
DTEND;VALUE=DATE-TIME:20180119T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20180202T163000
DTEND;VALUE=DATE-TIME:20180202T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20180420T163000
DTEND;VALUE=DATE-TIME:20180420T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20180427T163000
DTEND;VALUE=DATE-TIME:20180427T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20180518T163000
DTEND;VALUE=DATE-TIME:20180518T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20180608T163000
DTEND;VALUE=DATE-TIME:20180608T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20180622T163000
DTEND;VALUE=DATE-TIME:20180622T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20180713T163000
DTEND;VALUE=DATE-TIME:20180713T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20181015T140000
DTEND;VALUE=DATE-TIME:20181015T150000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20181026T163000
DTEND;VALUE=DATE-TIME:20181026T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20181109T163000
DTEND;VALUE=DATE-TIME:20181109T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20181116T163000
DTEND;VALUE=DATE-TIME:20181116T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20181127T163000
DTEND;VALUE=DATE-TIME:20181127T173000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20190125T163000
DTEND;VALUE=DATE-TIME:20190125T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20190201T163000
DTEND;VALUE=DATE-TIME:20190201T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20190503T163000
DTEND;VALUE=DATE-TIME:20190503T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20190517T163000
DTEND;VALUE=DATE-TIME:20190517T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20190614T163000
DTEND;VALUE=DATE-TIME:20190614T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20190628T163000
DTEND;VALUE=DATE-TIME:20190628T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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.
LOCATION:Seminar Room 0.03\, ETP
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Andreas Laeuchli
DTSTART;VALUE=DATE-TIME:20190712T163000
DTEND;VALUE=DATE-TIME:20190712T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20191011T163000
DTEND;VALUE=DATE-TIME:20191011T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20191115T163000
DTEND;VALUE=DATE-TIME:20191115T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20191129T163000
DTEND;VALUE=DATE-TIME:20191129T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20191206T163000
DTEND;VALUE=DATE-TIME:20191206T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20200110T163000
DTEND;VALUE=DATE-TIME:20200110T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20200117T163000
DTEND;VALUE=DATE-TIME:20200117T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20200424T163000
DTEND;VALUE=DATE-TIME:20200424T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20200508T163000
DTEND;VALUE=DATE-TIME:20200508T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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;VALUE=DATE-TIME:20200612T163000
DTEND;VALUE=DATE-TIME:20200612T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
UID:0000001530@events.thp.uni-koeln.de
DESCRIPTION:Susanna Manrubia\, Centro Nacional de Biotecnologia\, Madrid\n
\nPredictability: Can we precisely forecast the turning forecast the turni
ng point and end of an epidemic by fitting past data?\n\nNo\, we can’t.
The time at which the growth in the number of infected individuals halts a
nd starts decreasing cannot be calculated with certainty before the turnin
g point is actually attained. This assertion is illustrated by adding to a
standard SIR model a new class for confined individuals. A Bayesian fit t
o the on-going COVID-19 pandemic in Spain shows that a slow-down in the nu
mber of newly infected individuals during the expansion phase allows to in
fer neither the precise position of the maximum nor whether the measures t
aken will bring the propagation to the inhibition regime. Our study warns
against precise forecasts of the evolution of epidemics based on mean-fiel
d\, effective models\, and supports that only probabilities of different o
utcomes can be confidently given.\n\nContact Person: Joachim Krug
LOCATION:Online via Zoom
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Eva-Maria Graefe
DTSTART;VALUE=DATE-TIME:20200619T163000
DTEND;VALUE=DATE-TIME:20200619T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
UID:0000001534@events.thp.uni-koeln.de
DESCRIPTION:Eva-Maria Graefe\, Imperial College\, London\n\ntba\n\n\n\nCon
tact Person: S. Diehl
LOCATION:Online via Zoom
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Anne Nielsen
DTSTART;VALUE=DATE-TIME:20200626T163000
DTEND;VALUE=DATE-TIME:20200626T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
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
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Raquel Queiroz
DTSTART;VALUE=DATE-TIME:20200703T163000
DTEND;VALUE=DATE-TIME:20200703T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
UID:0000001532@events.thp.uni-koeln.de
DESCRIPTION:Raquel Queiroz\, Weizmann Institute\n\ntba\n\n\n\nContact Pers
on: S. Diehl
LOCATION:Online via Zoom
END:VEVENT
BEGIN:VEVENT
SUMMARY:TPK | Peidong Yu
DTSTART;VALUE=DATE-TIME:20200710T163000
DTEND;VALUE=DATE-TIME:20200710T180000
DTSTAMP;VALUE=DATE-TIME:20200602T081403Z
UID:0000001536@events.thp.uni-koeln.de
DESCRIPTION:Peidong Yu\, ITP Cologne and DLR\n\nVelocity Distribution of a
Homogeneously Cooling Granular Gas\n\n\n\nContact Person: Joachim Krug
LOCATION:Online via Zoom
END:VEVENT
END:VCALENDAR