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BEGIN:VEVENT
SUMMARY:Projective construction of the Zk Read-Rezayi fractional quantum H
all states
DTSTART;VALUE=DATE-TIME:20160519T080000Z
DTEND;VALUE=DATE-TIME:20160519T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6537@indico.fysik.su.se
DESCRIPTION:Speakers: Cecile Repellin ()\nThe Zk Read-Rezayi series1 is a
well known sequence of \nfractional quantum Hall (FQH) states with non-Abe
lian \ntopological order. The k = 1 member of this series is the \n(Abelia
n) Laughlin state. The k = 2 member of this series is \nthe Moore-Read3 st
ate supporting Majorana excitations and a \nwell studied candidate state f
or the FQH plateau of electrons \nat ν = 5/2. The Zk=3 Read- Rezayi state
supports Fibonacci \nanyons\, which can in principle be used to perform t
he \noperations of a universal topological quantum computer. The \nZk Read
-Rezayi series can be obtained using projective \nconstructions\, by start
ing from the Laughlin state as a parent \nstate. \nIn the simplest version
of the projective construction\, the \nbosonic Moore-Read state (Zk=2) is
written by symmetrizing \nthe product of two bosonic Laughlin wave functi
ons. On the \ntorus\, this construction does not yield the Moore-Read stat
e \nfor an odd number of particles in finite size. We show that \nintroduc
ing a defect allowing the bosons to go from one layer \nto the next can re
medy this problem. This obstruction also \nappears in the more generic cas
e of the projective \nconstruction of the bosonic Zk Read-Rezayi states\,
and is \nresolved similarly. The projective construction could provide \na
n avenue to write higher k members of the Zk series in the \nmatrix produc
t state language. In this context\, our new \nconstruction scheme should a
llow us to recover all topological \nsectors of the SU(2)k theory starting
only from the Laughlin \nstate. Beyond model states\, the projective cons
truction can \nalso be used to describe the neutral excitations above the
\nRead-Rezayi states. I will explore the accuracy of this \napproximation
in the case of the Moore-Read state neutral \nmode. Finally\, I will discu
ss the possibility that a microscopic \ninterlayer coupling term might phy
sically realize the \nsymmetrization in a bilayer system.\n\nhttps://indic
o.fysik.su.se/event/4989/contributions/6537/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6537/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Variational Tensor Network Renormalization in Imaginary Time: Benc
hmark results in the quantum compass model and the Hubbard model
DTSTART;VALUE=DATE-TIME:20160524T080000Z
DTEND;VALUE=DATE-TIME:20160524T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6538@indico.fysik.su.se
DESCRIPTION:Speakers: Piotr Czarnik ()\nThe Gibbs operator $e^{−\\beta H
}$ for a two-dimensional \n(2D) lattice system with a Hamiltonian H can be
represented \nby a three-dimensional tensor network\, the third dimension
\nbeing the imaginary time (inverse temperature) $\\beta$. \nCoarse-grain
ing the network along $beta$ results in a 2D \nprojected entangled-pair op
erator (PEPO) with a finite bond \ndimension D. The coarse-graining is per
formed by a tree \ntensor network of isometries. The isometries are optimi
zed \nvariationally --- taking into account full tensor environment --\n-
to maximize the accuracy of the PEPO. The algorithm is \napplied to the is
otropic quantum compass model on an \ninfinite square lattice near a symme
try-breaking phase \ntransition at finite temperature. From the linear sus
ceptibility \nin the symmetric phase and the order parameter in the \nsymm
etry-broken phase the critical temperature is estimated \nat $T_c=0.0606(4
)J$\, where J is the isotropic coupling \nconstant between S=1/2 pseudospi
ns. The algorithm is also \napplied to the two-dimensional Hubbard model o
n an infinite \nsquare lattice. Benchmark results are obtained that are \n
consistent with the best dynamical mean field theory (DCA - \ndynamical cl
uster approximation) and power series \nexpansion (NLCE - numerically li
nked cluster expansion) in \nthe regime of parameters where these more c
onventional \nmethods yield mutually consistent results.\n\nhttps://indico
.fysik.su.se/event/4989/contributions/6538/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6538/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Feynman Path Integrals over Matrix Product States
DTSTART;VALUE=DATE-TIME:20160506T091500Z
DTEND;VALUE=DATE-TIME:20160506T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6539@indico.fysik.su.se
DESCRIPTION:Speakers: Andrew Green ()\nTensor networks embody deep insight
s about the \nentanglement structure of many-body quantum systems. In \non
e dimension\, they have led to algorithms that can \ndetermine groundstate
s and follow time evolution with \nremarkable precision. Entanglement is t
reated in a very \ndifferent way in field theories of quantum systems. T
hese \nare constructed in such a way that the saddle points do not \nsuppo
rt entanglement – which is introduced by instanton or \nfluctuation corr
ections.\n We lift some of the insights about entanglement structure \nfr
om tensor networks to field theory. Our approach is to \nexplicitly constr
uct a field integral for the partition function \nover matrix product stat
es\, rather than coherent states. The \nsaddle points of such a theory sup
port entanglement in a way \nthat bears interesting comparison with fluctu
ation and \ninstanton corrections to the usual field theory. In contrast t
o \nnumerical applications of tensor networks\, where the bond \norder is
increased until a certain degree of accuracy is \nattained\, in this field
theoretical application\, qualitatively new \nfeatures appear even at low
bond order. We demonstrate this \nby discussing the field theory of certa
in deconfined quantum \ncritical points.\n\nhttps://indico.fysik.su.se/eve
nt/4989/contributions/6539/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6539/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fractional chiral metals
DTSTART;VALUE=DATE-TIME:20160511T091500Z
DTEND;VALUE=DATE-TIME:20160511T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6540@indico.fysik.su.se
DESCRIPTION:Speakers: Jens Bardarson ()\nhttps://indico.fysik.su.se/event/
4989/contributions/6540/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6540/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Topological phenomena in periodically driven systems: the role o
f disorder and interactions
DTSTART;VALUE=DATE-TIME:20160523T091500Z
DTEND;VALUE=DATE-TIME:20160523T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6541@indico.fysik.su.se
DESCRIPTION:Speakers: Erez Berg ()\nPeriodically driven quantum systems\,
such as \nsemiconductors subject to light and cold atoms in optical \nla
ttices\, provide a noveland versatile platform for realizing \ntopologica
l phenomena. Some of these are analogs of \ntopological insulators andsup
erconductors\, attainable also in \nstatic systems\; others are unique to
the periodically driven \ncase. I will describe how periodic \ndriving\,
disorder\, and interactions can conspire to give rise to \nnew robust s
teady states\, with no analogues in static \nsystems. In disordered two-di
mensional driven systems\, a \nphase with chiral edge states and fully l
ocalized bulk states is \npossible\; this phase can realize a non-adiabati
c quantized \ncharge pump. In interacting one dimensional driven systems
\, \ncurrent carrying states with excessively long life times can \narise.
\n\nhttps://indico.fysik.su.se/event/4989/contributions/6541/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6541/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Realizing all so(N)_1 quantum criticalities in symmetry protected
cluster models
DTSTART;VALUE=DATE-TIME:20160525T080000Z
DTEND;VALUE=DATE-TIME:20160525T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6542@indico.fysik.su.se
DESCRIPTION:Speakers: Ville Lahtinen ()\nWe show that all so(N)1 universal
ity class quantum \ncriticalities emerge when one-dimensional generalized
cluster \nmodels are perturbed with Ising or Zeeman terms. Each \ncritical
point is described by a low-energy theory of N linearly \ndispersing ferm
ions\, whose spectrum we show to precisely \nmatch the prediction by so(N)
1 conformal field theory. \nFurthermore\, by an explicit construction we s
how that all the \ncluster models are dual to non-locally coupled transver
se field \nIsing chains\, with the universality of the so(N)1 criticality
\nmanifesting itself as N of these chains becoming critical. This \ndualit
y also reveals that the symmetry protection of cluster \nmodels arises fro
m the underlying Ising symmetries and it \nenables the identification of l
ocal representations for the \nprimary fields of the so(N)1conformal field
theories. For the \nsimplest and experimentally most realistic case that
\ncorresponds to the original one-dimensional cluster model \nwith local t
hree-spin interactions\, our results show that the \nsu(2)2≃so(3)1 Wess-
Zumino-Witten model can emerge in a \nlocal\, translationally invariant an
d Jordan-Wigner solvable \nspin-1/2 model. Our results pave the way for cl
assifying \ncriticalities between symmetry-protected topological states.\n
\nhttps://indico.fysik.su.se/event/4989/contributions/6542/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6542/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Symmetry twisting in entanglement
DTSTART;VALUE=DATE-TIME:20160527T080000Z
DTEND;VALUE=DATE-TIME:20160527T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6543@indico.fysik.su.se
DESCRIPTION:Speakers: Shunji Matsuura ()\nEntanglement and symmetries are
two fundamental concepts \nin classifying quantum states. We consider a ne
w type of \nentanglement entropy which is enriched by symmetry \ntwisting\
, and show how the entropy distinguishes quantum \nstates\, including symm
etry protected and enriched \ntopological phases. This is based on works w
ith Wen\, Ryu\, \nHung\, and Caputa.\n\nhttps://indico.fysik.su.se/event/4
989/contributions/6543/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6543/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Self-organized semi-metals on grain boundaries in topological band
insulators
DTSTART;VALUE=DATE-TIME:20160526T080000Z
DTEND;VALUE=DATE-TIME:20160526T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6544@indico.fysik.su.se
DESCRIPTION:Speakers: Robert-Jan Slager ()\nSemi-metals are characterized
by nodal band structures that \ngive rise to exotic electronic properties.
The stability of Dirac \nsemi-metals\, such as graphene in two spatial d
imensions \n(2D)\, requires the presence of lattice symmetries\, while aki
n \nto the surface states of topological band insulators\, Weyl \nsemi-met
als in three spatial dimensions (3D) are protected \nby band topology. I w
ill show that in the bulk of topological \nband insulators\, self-organize
d topologically protected semi-\nmetals can emerge along a grain boundary\
, a ubiquitous \nextended lattice defect in any crystalline material. In a
ddition \nto experimentally accessible electronic transport \nmeasurements
\, these states exhibit a valley anomaly that \ninfluences the edge spin t
ransport in two spatial dimensions \n(2D)\, whereas in 3D they appear as g
raphene-like states that \nshould exhibit an odd-integer quantum Hall effe
ct. The \ngeneral mechanism underlying these novel semi-metals\, \nbeing t
he hybridization of spinon modes bound to the grain \nboundary\, suggests
that topological semi-metals can emerge \nin any topological material wh
ere lattice dislocations bind \nlocalized topological modes.\n\nhttps://in
dico.fysik.su.se/event/4989/contributions/6544/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6544/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Recent advances with iPEPS: simulations of the 2D Hubbard model\,
improved energy extrapolations\, and variational optimization
DTSTART;VALUE=DATE-TIME:20160524T091500Z
DTEND;VALUE=DATE-TIME:20160524T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6545@indico.fysik.su.se
DESCRIPTION:Speakers: Philippe Corboz ()\nIn this talk I report on recent
progress with infinite projected \nentangled-pair states (iPEPS) which is
a tensor network \nansatz for 2D wave functions in the thermodynamic limit
. I \npresent simulation results for the 2D t-J and Hubbard models\, \nfor
bond dimensions up to D=16\, which reveal an extremely \nclose competitio
n between a uniform d-wave superconducting \nstate and different types of
stripe states. The iPEPS \nvariational energies are lower than previous st
ate-of-the-art \nvariational results for large 2D systems which demonstrat
es \nthe competitiveness of the approach. A key factor to \ndetermine the
true ground state among several competing \nstates is to have an accurate
estimate of their energies in the \ninfinite bond dimension D limit. Howev
er\, a simple \nextrapolation in 1/D often does not provide an accurate \n
result. We show how to improve these estimates by an \nextrapolation based
on a truncation error which is computed \nwithin the iPEPS imaginary time
evolution algorithm. Finally\, I \npresent a variational optimization sch
eme for iPEPS which \nyields a higher accuracy than previous ground state
\nalgorithms.\n\nhttps://indico.fysik.su.se/event/4989/contributions/6545/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6545/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Entanglement and the fermion sign problem in auxiliary field quant
um Monte Carlo simulations
DTSTART;VALUE=DATE-TIME:20160503T080000Z
DTEND;VALUE=DATE-TIME:20160503T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6546@indico.fysik.su.se
DESCRIPTION:Speakers: Simon Trebst ()\nQuantum Monte Carlo simulations of
fermions are hampered \nby the notorious sign problem whose most striking
\nmanifestation is an exponential growth of sampling errors \nwith the nu
mber of particles. With the sign problem known to \nbe an NP-hard problem
and any generic solution thus highly \nelusive\, the Monte Carlo sampling
of interacting many-\nfermion systems is commonly thought to be restricte
d to a \nsmall class of model systems for which a sign-free basis has \nbe
en identified. Here we demonstrate that entanglement \nmeasures\, in part
icular the so-called Renyi entropies\, can \nintrinsically exhibit a certa
in robustness against the sign \nproblem in auxiliary-field quantum Monte
Carlo approaches \nand possibly allow for the identification of global gr
ound-state \nproperties via their scaling behavior even in the presence o
f a \nstrong sign problem. We corroborate these findings via \nnumerical s
imulations of fermionic quantum phase transitions \nof spinless fermions o
n the honeycomb lattice at and below \nhalf-filling.\n\nhttps://indico.fy
sik.su.se/event/4989/contributions/6546/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6546/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Topological phase transitions and anyon condensation in tensor net
works: A holographic perspective
DTSTART;VALUE=DATE-TIME:20160510T091500Z
DTEND;VALUE=DATE-TIME:20160510T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6548@indico.fysik.su.se
DESCRIPTION:Speakers: Norbert Schuch ()\nWe investigate topological phases
and phase transitions in \nthe framework of tensor network models. We dis
cuss the role \nof symmetries in this description\, and show how it allows
to \nrelate topological phases and transitions between them to \nsymmetry
broken and symmetry protected phases exhibited \nby the transfer operator
of the system\, i.e.\, at the boundary. \nThis is accomplished by trans
lating the string-like topological \nexcitations in the 2D bulk to string
order parameters \ncharacterizing the different phases under symmetry at t
he \nboundary. We show that by taking into account the \nconstraints ari
sing from complete positivity of the transfer \noperator\, which restricts
the possible phases\nat the boundary\, this yields a complete characteriz
ation of all \npossible ways in which topological phase transitions can oc
cur \nthrough condensation and confinement of anyons.\n\nhttps://indico.fy
sik.su.se/event/4989/contributions/6548/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6548/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Bridging coupled wires and a lattice Hamiltonian for two-component
bosonic quantum Hall states
DTSTART;VALUE=DATE-TIME:20160504T091500Z
DTEND;VALUE=DATE-TIME:20160504T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6549@indico.fysik.su.se
DESCRIPTION:Speakers: Yohei Fuji ()\nWe investigate a model of hard-core b
osons with correlated \nhopping on the honeycomb lattice in an external ma
gnetic \nfield by means of a coupled-wire approach. It has been \nnumerica
lly shown that this model exhibits at half filling the \nbosonic integer q
uantum Hall (BIQH) state\, which is a \nsymmetry-protected topological pha
se protected by the U(1) \nparticle conservation. By combining the bosoniz
ation \napproach and a coupled-wire construction\, we analytically \nconfi
rm this finding and show that it even holds in the\nstrongly anisotropic (
quasi-one-dimensional) limit. We further \nargue that a phase transition b
etween two different BIQH \nphases is in a deconfined quantum critical poi
nt described by \ntwo copies of the (2+1)-dimensional O(4) nonlinear sigma
\nmodel with a topological theta term. Finally we predict a \npossible fr
actional quantum Hall state\, the Halperin (221)\nstate\, at 1/6 filling.\
n\nhttps://indico.fysik.su.se/event/4989/contributions/6549/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6549/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Fractional quantum Hall models in lattice systems from conformal f
ield theory
DTSTART;VALUE=DATE-TIME:20160506T080000Z
DTEND;VALUE=DATE-TIME:20160506T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6550@indico.fysik.su.se
DESCRIPTION:Speakers: Anne Nielsen ()\nIn recent years\, there has been mu
ch interest in finding \nfractional quantum Hall models in lattice systems
\, both \nbecause it may lead to new ways to realize the fractional \nquan
tum Hall effect\, and because the lattice gives rise to new \neffects and
possibilities. Here we show that conformal field \ntheory is a power full
tool to construct fractional quantum \nHall models in lattice systems. We
build various fractional \nquantum Hall states with and without anyons as
infinite-\ndimensional-matrix product states of conformal fields. We use \
nconformal field theory to derive few-body Hamiltonians for \nwhich the st
ates are exact ground states\, and we analyze the \nproperties of the wave
functions using analytical and \nnumerical tools. Finally\, we discuss rec
ent results on how one \ncan obtain models interpolating between lattice f
ractional \nquantum Hall systems and continuum fractional quantum Hall \ns
ystems.\n\nhttps://indico.fysik.su.se/event/4989/contributions/6550/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6550/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Universal Signatures of Quantum Critical Points from Finite-Size T
orus Spectra: A Window into the Operator Content of Higher-Dimensional Con
formal Field Theories.
DTSTART;VALUE=DATE-TIME:20160503T091500Z
DTEND;VALUE=DATE-TIME:20160503T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6551@indico.fysik.su.se
DESCRIPTION:Speakers: Andreas Läuchli ()\nThe low-energy spectra of many
body systems on a torus\, of \nfinite size L\, are well understood in magn
etically ordered and \ngapped topological phases. However\, the spectra at
quantum \ncritical points separating such phases are largely unexplored \
nfor 2+1D systems. Using a combination of analytical and \nnumerical techn
iques\, we show that the low-energy torus \nspectrum at criticality provid
es a universal fingerprint of the \nunderlying quantum field theory\, with
the energy levels given \nby universal numbers times 1/L. We highlight th
e implications \nof a neighboring topological phase on the spectrum by \ns
tudying the Ising* transition\, in the example of the toric \ncode in a lo
ngitudinal field\, and advocate a phenomenological \npicture that provides
insight into the operator content of the \ncritical field theory.\n\nhttp
s://indico.fysik.su.se/event/4989/contributions/6551/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6551/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Energy projection and modified Laughlin states
DTSTART;VALUE=DATE-TIME:20160504T080000Z
DTEND;VALUE=DATE-TIME:20160504T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6552@indico.fysik.su.se
DESCRIPTION:Speakers: Mikael Fremling ()\nWe develop a method to efficient
ly calculate trial wave \nfunctions for quantum Hall systems which involve
projection \nonto the lowest Landau level. The method essentially replace
s \nlowest Landau level projection by projection onto the M \nlowest eigen
states of a suitably chosen hamiltonian acting \nwithin the lowest Landau
level. The resulting "energy \nprojection" is a controlled approximation t
o the exact lowest \nLandau level projection which improves with increasin
g M. It \nallows us to study projected trial wave functions for system \ns
izes close to the maximal sizes that can be reached by exact \ndiagonaliza
tion and can be straightforwardly applied in any \ngeometry. As a first ap
plication and test case\, we study a \nclass of trial wave functions first
proposed by Girvin and Jach\, \nwhich are modifications of the Laughlin s
tates involving a \nsingle real parameter.\n\nhttps://indico.fysik.su.se/e
vent/4989/contributions/6552/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6552/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Spontaneous currents and Majorana fermions from magnetic impuritie
s on spin-orbit coupled superconductors
DTSTART;VALUE=DATE-TIME:20160520T091500Z
DTEND;VALUE=DATE-TIME:20160520T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6553@indico.fysik.su.se
DESCRIPTION:Speakers: Annica Black-Schaffer ()\nDepositing magnetic impuri
ties or islands on top of spin-orbit \ncoupled superconductors can generat
e a topological \nsuperconducting state. For one-dimensional impurity wire
s\, a \nnon-trivial topology will give rise to Majorana fermions \nappeari
ng at the end points of the wire\, whereas for magnetic \nislands edge sta
tes disperse across the bulk energy gap.\nIn this talk I will focus on sev
eral recent results for these \nsystems. I will show that persistent curre
nts are generated \naround magnetic impurities. The currents are independe
nt on \ntopology\, but still generally peak around the topological phase \
ntransition. I will also show how a self-consistent solution for \nthe sup
erconducting state results in a heavily suppressed \nsuperconducting order
parameter at the impurity sites\, which \ncan even experience a pi-shift.
This pi-shift can be explained \nby impurity-induced quasiparticles being
completely out of \nphase with the condensate.\n\nhttps://indico.fysik.su
.se/event/4989/contributions/6553/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6553/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Symmetry Protected Topological Phases of fermions
DTSTART;VALUE=DATE-TIME:20160519T091500Z
DTEND;VALUE=DATE-TIME:20160519T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6554@indico.fysik.su.se
DESCRIPTION:Speakers: Lukasz Fidkowski ()\nTopological insulators constitu
te a different phase of quantum \nmatter from ordinary insulators\, despit
e not breaking any \nsymmetries. They are an example of a `symmetry prote
cted \ntopological' phase\, in that they exhibit exotic phenomena\, \nname
ly gapless surface modes\, that are entirely protected by \ntime reversal
symmetry. Motivated by this\, one can classify \nall possible non-trivial
topological insulators in all dimensions \nand symmetry classes at the le
vel of band structures. \nHowever\, the role of interactions in this sche
me is still not \ncompletely understood. In this talk I'll describe our r
ecent \nwork on classifying interacting analogues of topological \ninsulat
ors\, and constructing exactly solvable lattice \nrealizations of them\, w
hich may allow them to be targeted by \nnumerical algorithms.\n\nhttps://i
ndico.fysik.su.se/event/4989/contributions/6554/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6554/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Chiral edge modes of a critical spin liquid
DTSTART;VALUE=DATE-TIME:20160517T080000Z
DTEND;VALUE=DATE-TIME:20160517T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6555@indico.fysik.su.se
DESCRIPTION:Speakers: Didier Poilblanc ()\nProtected chiral edge modes are
a well-known signature of \ntopologically ordered phases like the Fractio
nal Quantum Hall \nStates (FQHS).\nUsing the framework of projected entang
led pair states \n(PEPS) on the square lattice\, we construct a family of\
nchiral spin-1/2 quantum spin liquids with $\\mathbb{Z}_2$ \ngauge symmet
ry and analyze in full details the properties of \nthe edge modes. Surpris
ingly\,\nwe show that the latter can be well described by a chiral \nConf
ormal Field Theory of free bosons (SU(2)$_1$)\, as for \nthe $\\nu=1/2$ (b
osonic) gapped\nLaughlin state\, despite the fact that our numerical data
\nsuggest a critical bulk.\nWe propose that our family of PEPS physically
describes a \nboundary between a chiral topological phase and a trivial \n
phase\nand might be closely connected to an (unknown) analogous \nFQHS.\n\
nhttps://indico.fysik.su.se/event/4989/contributions/6555/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6555/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Topological Quantum Infidelity
DTSTART;VALUE=DATE-TIME:20160512T091500Z
DTEND;VALUE=DATE-TIME:20160512T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6556@indico.fysik.su.se
DESCRIPTION:Speakers: Kirill Shtengel ()\nhttps://indico.fysik.su.se/event
/4989/contributions/6556/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6556/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Ergodicity\, entanglement\, and many-body localization
DTSTART;VALUE=DATE-TIME:20160517T091500Z
DTEND;VALUE=DATE-TIME:20160517T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6557@indico.fysik.su.se
DESCRIPTION:Speakers: Dmitry Abanin ()\nWe are used to describing systems
of many particles by \nstatistical mechanics. However\, recently it was re
alized that \nthe basic postulate of statistical mechanics – ergodicity
-- \nbreaks down in so-called many-body localized systems\, \nwhere disord
er prevents particle transport and \nthermalization. In this talk\, I will
describe a theory of the \nmany-body localized (MBL) phase\, based on new
insights \nfrom quantum entanglement. I will argue that\, in contrast to
\nergodic systems\, MBL eigenstates are not highly entangled\, \nbut rathe
r obey so-called area law\, typical of ground states in \ngapped systems.
I will use this fact to show that MBL phase \nis characterized by an infin
ite number of emergent local \nconservation laws\, in terms of which the H
amiltonian acquires \na universal form. Turning to the experimental implic
ations\, I \nwill show that MBL systems exhibit a universal response to \n
quantum quenches: surprisingly\, entanglement shows \nlogarithmic in time
growth\, reminiscent of glasses\, while local \nobservables exhibit power-
law approach to “equilibrium” \nvalues. I will also introduce a criter
ion for the transition \nbetween many-body localized and ergodic phases\,
based on \nthe response of the system to a local perturbation.\n\nhttps://
indico.fysik.su.se/event/4989/contributions/6557/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6557/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Turning a corner on entanglement entropy
DTSTART;VALUE=DATE-TIME:20160512T080000Z
DTEND;VALUE=DATE-TIME:20160512T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6558@indico.fysik.su.se
DESCRIPTION:Speakers: Roger Melko ()\nhe entanglement entropy of a quantum
critical system \nreceives a logarithmic contribution when the entangling
\nboundary contains a sharp corner. Numerical calculations \nindicate t
hat for the Wilson-Fisher fixed point in 2+1 \ndimensions\, the coefficien
t of this logarithm is universal and \ncontains low-energy information\, s
caling for example with the \nnumber of vector components of the field the
ory. Recently\, \nthese numerical results have been confirmed analytical
ly\, \nrevealing a relationship between the corner coefficient and a \ncen
tral charge defined from the stress tensor two-point \nfunction. The combi
nation of analytical understanding and \neasy numerical accessibility prom
ises to make the corner \nentanglement an important theoretical tool\, pro
viding a new \nwindow on universality for free and interacting systems ali
ke.\n\nhttps://indico.fysik.su.se/event/4989/contributions/6558/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6558/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Self-organized topological superconductivity in a Yu-Shiba-Rusinov
chain
DTSTART;VALUE=DATE-TIME:20160511T080000Z
DTEND;VALUE=DATE-TIME:20160511T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6559@indico.fysik.su.se
DESCRIPTION:Speakers: Jens Paaske ()\nIn this talk I show how a chain of m
agnetic moments \nexchange coupled to a conventional three-dimensional \ns
uperconductor is unstable towards the formation of a \nmagnetic spiral sta
te. Beyond weak exchange coupling the \nspiral wave vector greatly exceeds
the inverse \nsuperconducting coherence length as a result of the strong
\nspin-spin interaction mediated through the subgap band of \nYu-Shiba-Rus
inov states. Moreover\, the simple spin-spin \nexchange description breaks
down as the subgap band \ncrosses the Fermi energy\, wherein the spiral p
hase becomes \nstabilized by the spontaneous opening of a p-wave \nsuperco
nducting gap within the band. This leads to the \npossibility of electron-
driven topological superconductivity \nwith Majorana boundary modes using
magnetic atoms on \nsuperconducting surfaces.\n\nhttps://indico.fysik.su.s
e/event/4989/contributions/6559/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6559/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Steady States of Infinite-Size Dissipative Quantum Chains via Imag
inary Time Evolution
DTSTART;VALUE=DATE-TIME:20160510T080000Z
DTEND;VALUE=DATE-TIME:20160510T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6560@indico.fysik.su.se
DESCRIPTION:Speakers: Ying-Jer Kao ()\nWe show how to use imaginary time e
volution of matrix \nproduct density operators with the infinite time-evol
ving \nblock decimation algorithm to determine the nonequilibrium \nsteady
states of one-dimensional dissipative quantum lattices \nin the thermodyn
amic limit. We provide a demonstration with \nthe transverse field quantum
Ising chain. The approach is \nalso amenable to higher dimensions.\n\nhtt
ps://indico.fysik.su.se/event/4989/contributions/6560/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6560/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Nonsymmorphic topological crystalline insulators and superconducto
rs: Mobius twists in surface states
DTSTART;VALUE=DATE-TIME:20160509T091500Z
DTEND;VALUE=DATE-TIME:20160509T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6561@indico.fysik.su.se
DESCRIPTION:Speakers: Masatoshi Sato ()\nUsing the twisted equivariant K-t
heory\, we complete a \nclassification of topological crystalline insulato
rs and \nsuperconductors in the presence of additional order-two \nnonsymm
orphic space group symmetries. The order-two \nnonsymmorphic space groups
include half lattice translation \nwith Z2 flip\, glide\, two-fold screw\,
and their magnetic space \ngroups. It is pointed out that the nonsymmorph
ic space \ngroups allow ℤ2 topological phases even in the absence of \nt
ime-reversal and/or particle-hole symmetries. Furthermore\, \nthe coexiste
nce of the nonsymmorphic space group with the \ntime-reversal and/or parti
cle-hole symmetries provides novel \nℤ4 topological phases. We argue tha
t the corresponding \nsurface states have Mobius twisted structures in the
\nmomentum space.\n\nhttps://indico.fysik.su.se/event/4989/contributions/
6561/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6561/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Spin liquids on kagome lattice and symmetry protected topological
phase
DTSTART;VALUE=DATE-TIME:20160509T080000Z
DTEND;VALUE=DATE-TIME:20160509T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6562@indico.fysik.su.se
DESCRIPTION:Speakers: Yin-Chen He ()\nIn my talk I will introduce the spin
liquid phases that occur in \nkagome antiferromagnets\, and discuss their
physical origin \nthat are closely related with the newly discovered symm
etry \nprotected topological phase (SPT). I will first present our \nnumer
ical (DMRG) study on the kagome XXZ spin model that \nexhibits two disti
nct spin liquid phases\, namely the chiral spin \nliquid and the kagome s
pin liquid (the groundstate of the \nnearest neighbor kagome Heisenberg mo
del). Both phases \nextend from the extreme easy-axis limit\, through SU(
2) \nsymmetric point\, to the pure easy-plane limit. The two \nphases are
separated by a continuous phase transition. \nMotivated by these numerica
l results\, I will then focus on the \neasy-axis kagome spin system\, and
reformulate it as a lattice \ngauge model. Such formulation enables us t
o achieve a \ncontrolled theoretical description for the spin liquid phase
s. \nWe then show that the chiral spin liquid is indeed a gauged \nU(1)
SPT phase. On the other hand\, we also propose that the \nkagome spin liqu
id is a critical spin liquid phase\, which can be \nconsidered as a gauged
deconfined critical point between a \nSPT and a superfluid phase.\n\nhttp
s://indico.fysik.su.se/event/4989/contributions/6562/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6562/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Glassy dynamics as a quantum problem
DTSTART;VALUE=DATE-TIME:20160518T091500Z
DTEND;VALUE=DATE-TIME:20160518T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6563@indico.fysik.su.se
DESCRIPTION:Speakers: Zohar Nussinov ()\nWe review the underpinning of the
microcanonical ensemble and the \nmore refined (and explicitly quantum) "
Eigenstate Thermalization \nHypothesis". We then find and apply a simple c
orollary of these to \nanalyze the evolution of a liquid upon supercooling
to form a \nstructural glass.\nSimple theoretical considerations lead to
predictions for general \nproperties of supercooled liquids. Amongst other
things\, a collapse of \nthe viscosity of glass formers is predicted from
this theory. This \ncollapse indeed occurs over 16 decades of relaxation
times for all \nknown types of glass formers.\n\nhttps://indico.fysik.su.s
e/event/4989/contributions/6563/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6563/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum Hall Edges with Hard Confinement: Exact Solutions and Nu
merics beyond Luttinger Liquid
DTSTART;VALUE=DATE-TIME:20160516T080000Z
DTEND;VALUE=DATE-TIME:20160516T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6564@indico.fysik.su.se
DESCRIPTION:Speakers: Steve Simon ()\nWe consider a Laughlin droplet in a
confining potential which \nis very steep but also weak compared to the ul
tra-short \nranged inter-particle interactions. We find that the \neigen
states have a Jack polynomial structure\, and have an \nenergy spectrum wh
ich is extremely different from the well-\nknown Luttinger liquid edge.\n\
nhttps://indico.fysik.su.se/event/4989/contributions/6564/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6564/
END:VEVENT
BEGIN:VEVENT
SUMMARY:New Fermions
DTSTART;VALUE=DATE-TIME:20160513T080000Z
DTEND;VALUE=DATE-TIME:20160513T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6565@indico.fysik.su.se
DESCRIPTION:Speakers: Bogdan Bernevig ()\nIn quantum field theory\, we lea
rn that fermions come in three \nvarieties: Majorana\, Weyl\, and Dirac. I
n this paper\, we show \nthat this is not a complete classification. We fi
nd the types of \ncrystal symmetry-protected free fermionic excitations th
at \ncan occur in condensed matter systems\, going beyond the \nclassifica
tion of Majorana\, Weyl\, and Dirac particles. We \nexhaustively classify
linear and quadratic 3-\, 6- and 8- band \ncrossings stabilized by space g
roup symmetries in solid state \nsystems with spin-orbit coupling and time
-reversal symmetry. \nSeveral distinct types of fermions arise\, different
iated by their \ndegeneracies at and along high symmetry points\, lines\,
and \nsurfaces. For each new class of fermion\, we analyze its \ntopologic
al properties by constructing the low-energy \neffective Hamiltonian and c
omment on any possible \nexperimental signatures. Some notable consequence
s of \nthese fermions are the presence of Fermi arcs in non-Weyl \nsystems
\, the fermionic spin-1 generalization of a Weyl \nfermion\, and the exist
ence of Dirac lines. In addition\, we \npresent 18 candidate materials tha
t should realize these \nexotic fermions\, as verified by ab-initio calcul
ations. We also \npresent holographic fermions - fermions that can appear
only \nat the boundary of higher dimensional insulators\, and show \nthat
their connectivity in the Brillouin zone is described by an \nextension of
Group Cohomology to the Brillouin zone. For all \nthese systems we presen
t realistic materials.\n\nhttps://indico.fysik.su.se/event/4989/contributi
ons/6565/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6565/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Matrix product state representation of quasielectron wave function
s
DTSTART;VALUE=DATE-TIME:20160518T080000Z
DTEND;VALUE=DATE-TIME:20160518T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6566@indico.fysik.su.se
DESCRIPTION:Speakers: Jonas Kjäll ()\nRecently it has been shown that the
model wave functions \ndescribing the fractional quantum Hall (FQH) effec
t have an \nexact representation as matrix product states (MPS). This \nre
presentation is extremely useful for numerical calculation of \nFQH physic
s. However\, a crucial piece\, the implementation of \nthe non-local quasi
electron operator has been missing. We \nshow how to implement the quasi-e
lectron as an MPS for the \nLaughlin state and numerically compute the Ber
ry phases for \ndifferent excitations.\n\nhttps://indico.fysik.su.se/event
/4989/contributions/6566/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6566/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Quantum critical point of Dirac fermion mass generation without sp
ontaneous symmetry
DTSTART;VALUE=DATE-TIME:20160525T091500Z
DTEND;VALUE=DATE-TIME:20160525T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6567@indico.fysik.su.se
DESCRIPTION:Speakers: Zi-Yang Meng ()\nWe study a lattice model of interac
ting Dirac fermions in \n(2+1) dimension space-time with an SU(4) symmetry
. While \nincreasing interaction strength\, this model undergoes a \nconti
nuous quantum phase transition from the weakly \ninteracting Dirac semimet
al to a fully gapped and \nnondegenerate phase without condensing any Dira
c fermion \nbilinear mass operator. This unusual mechanism for mass \ngene
ration is consistent with recent studies of interacting \ntopological insu
lators/superconductors\, and also consistent \nwith recent progresses in l
attice QCD community.\n\nhttps://indico.fysik.su.se/event/4989/contributio
ns/6567/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6567/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Topological Defects on the Lattice
DTSTART;VALUE=DATE-TIME:20160520T080000Z
DTEND;VALUE=DATE-TIME:20160520T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6568@indico.fysik.su.se
DESCRIPTION:Speakers: Roger Mong ()\nWe construct topological defects in 2
D classical lattice models \nand 1D quantum chains. The defects satisfy
commutation \nrelations guaranteeing the partition function depends only o
n \ntopological properties of the defects. One useful \nconsequence is a
generalization of Kramers-Wannier duality \nto a wide class of height mod
els\, applicable on any surfaces. \n This enables us to derive modular tr
ansformations of \nconformal field theories (CFTs) directly from lattice \
nconsiderations. We will also discuss how to write chiral CFT \noperator
s on a lattice.\n\nhttps://indico.fysik.su.se/event/4989/contributions/656
8/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6568/
END:VEVENT
BEGIN:VEVENT
SUMMARY:"Bosonic" quantum phase transition of strongly interacting topolog
ical insulators: field theory\, Numerics\, and experimental platform
DTSTART;VALUE=DATE-TIME:20160523T080000Z
DTEND;VALUE=DATE-TIME:20160523T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6569@indico.fysik.su.se
DESCRIPTION:Speakers: Cenke Xu ()\nWe discuss our recent works on strongly
interacting bilayer \nquantum Spin Hall insulators with Sz conservation.
We \ndemonstrate that interaction will drive the system into a \n"bosonic"
symmetry protected topological phase\, in the sense \nthat bosonic modes
are gapless at the boundary\, while local \nfermion excitations are gapped
. Also\, at the bulk quantum \ncritical point between the topological and
trivial states\, \nbosonic modes close their gap\, while fermion modes rem
ain \ngapped. Thus this quantum critical point is a purely "bosonic" \ncon
formal field theory\, which is described by a 2+1d O(4) \nnonlinear sigma
model with a Theta term at Theta = Pi. All \nthese results are confirmed b
y both field theory analysis and \nalso quantum Monte Carlo simulation. We
also propose that \nthese physics can be well realized in bilayer graphen
e under \n(strong) out of plane magnetic field.\n\nhttps://indico.fysik.su
.se/event/4989/contributions/6569/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6569/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Many body localization and thermalization: insights from the entan
glement spectrum
DTSTART;VALUE=DATE-TIME:20160516T091500Z
DTEND;VALUE=DATE-TIME:20160516T101500Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6570@indico.fysik.su.se
DESCRIPTION:Speakers: Nicolas Regnault ()\nhttps://indico.fysik.su.se/even
t/4989/contributions/6570/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6570/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Stochastic Approach to Non-Equilibrium and Dissipative Many-Body Q
uantum Dynamics
DTSTART;VALUE=DATE-TIME:20160502T080000Z
DTEND;VALUE=DATE-TIME:20160502T090000Z
DTSTAMP;VALUE=DATE-TIME:20210723T184509Z
UID:indico-contribution-4989-6571@indico.fysik.su.se
DESCRIPTION:Speakers: Karyn Le Hur ()\nhttps://indico.fysik.su.se/event/49
89/contributions/6571/
LOCATION:Nordita\, Stockholm 122:026
URL:https://indico.fysik.su.se/event/4989/contributions/6571/
END:VEVENT
END:VCALENDAR