Quantum Matter

431 talks

S021

Collection Type

Series

Subject

Condensed Matter

Displaying 373 - 384 of 431

An Informal Discussion About Topological Gauge Theory, part 2

Xiao-Gang Wen
Massachusetts Institute of Technology (MIT) - Department of Physics

October 30, 2012

PIRSA:12100132
Synthetic non-Abelian anyons in fractional Chern insulators and beyond

Xiaoliang Qi
Stanford University
October 26, 2012

PIRSA:12100051
Condensed Matter
An informal discussion about topological gauge theory

Xiao-Gang Wen
Massachusetts Institute of Technology (MIT) - Department of Physics
October 23, 2012

PIRSA:12100129
Quantum Fields and Strings
Self-localization of a single hole in Mott antiferromagnets

Zheng-Yu Weng
Tsinghua University
October 19, 2012

PIRSA:12100077
Condensed Matter
Effect of thermal fluctuations in topological p-wave superconductors

Bela Bauer
Microsoft Corporation
September 21, 2012

PIRSA:12090039
Condensed Matter
Hamiltonian Theory of Fractional Chern Bands

Ramamurti Shankar
Yale University
September 14, 2012

PIRSA:12090047
Mathematical physics
Charge fractionalization and entanglement entropy for compressible phases in holography

Liza Huijse
Karius, Inc.
September 11, 2012

PIRSA:12090059
Condensed Matter
Multiplets in the Entanglement Spectrum

Ari Turner
Universiteit van Amsterdam

September 06, 2012

PIRSA:12090056
Topological Order in Spin Systems

Paul Fendley
University of Oxford
August 10, 2012

PIRSA:12080002
Particle Physics
Glass: The Cinderella Problem of Condensed Matter Physics

Anthony Leggett
University of Illinois Urbana-Champaign
August 03, 2012

PIRSA:12080001
Condensed Matter
Integer Quantum Hall Effect for Bosons: A Physical Realization

Senthil Todadri
Massachusetts Institute of Technology (MIT) - Department of Physics
July 27, 2012

PIRSA:12070013
Condensed Matter
Symmetry Protected Topological Phases; from Quantum Entanglement to Interaction Effects

Ashvin Vishwanath
Harvard University
July 27, 2012

PIRSA:12070012
Condensed Matter

An Informal Discussion About Topological Gauge Theory, part 2

Xiao-Gang Wen
Massachusetts Institute of Technology (MIT) - Department of Physics

October 30, 2012

PIRSA:12100132

Reference:
Topological gauge theories and group cohomology
Robbert Dijkgraaf and Edward Witten
http://projecteuclid.org/DPubS?service=UI&version=1.0&verb=Display&handle=euclid.cmp/1104180750

Braiding statistics approach to symmetry-protected topological phases
Michael Levin, Zheng-Cheng Gu
http://arxiv.org/abs/1202.3120
Synthetic non-Abelian anyons in fractional Chern insulators and beyond

Xiaoliang Qi
Stanford University
October 26, 2012

PIRSA:12100051
Condensed Matter
An exciting new prospect in condensed matter physics is the possibility of realizing fractional quantum Hall states in simple lattice models without a large external magnetic field, which are called fractional Chern insulators. A fundamental question is whether qualitatively new states can be realized on the lattice as compared with ordinary fractional quantum Hall states. Here we propose new symmetry-enriched topological states, topological nematic states, which are a dramatic consequence of the interplay between the lattice translational symmetry and topological properties of these fractional Chern insulators. The topological nematic states are realized in a partially filled flat band with a Chern number N, which can be mapped to an N-layer quantum Hall system on a regular lattice. However, in the topological nematic states the lattice dislocations become non-Abelian defects which create "worm holes" connecting the effective layers, and effectively change the topology of the space. Such topology-changing defects, which we name as "genons", can also be defined in other physical systems. We develop methods to compute the projective non-abelian braiding statistics of the genons, and we find the braiding is given by adiabatic modular transformations, or Dehn twists, of the topological state on the effective genus g surface. We find situations where the > genons have quantum dimension 2 and can be used for universal topological quantum computing (TQC), while the host topological state is by itself non-universal for TQC.
An informal discussion about topological gauge theory

Xiao-Gang Wen
Massachusetts Institute of Technology (MIT) - Department of Physics
October 23, 2012

PIRSA:12100129
Quantum Fields and Strings
Reference:
Topological gauge theories and group cohomology
Robbert Dijkgraaf and Edward Witten
http://projecteuclid.org/DPubS?service=UI&version=1.0&verb=Display&handle=euclid.cmp/1104180750

Braiding statistics approach to symmetry-protected topological phases
Michael Levin, Zheng-Cheng Gu
http://arxiv.org/abs/1202.3120
Self-localization of a single hole in Mott antiferromagnets

Zheng-Yu Weng
Tsinghua University
October 19, 2012

PIRSA:12100077
Condensed Matter
Anderson localization - quantum suppression of carrier diffusion due to disorders - is a basic notion of modern condensed matter physics. Here I will talk about a novel localization phenomenon totally contrary to this common wisdom. Strikingly, it is purely of strong interaction origin and occurs without the assistance of disorders. Specifically, by combined numerical (density matrix renormalization group) method and analytic analysis, we show that a single hole injected in a quantum antiferromagnetic ladder is generally self-localized even though the system respects the translational symmetry. The localization length is found to monotonically decrease with the increase of leg number, indicating stronger self-localization in the two-dimensional limit. We find that a peculiar coupling between the doped charge and the quantum spin background causes quantum interference among different hole paths. The latter brings the hole's itinerant motion to a halt, a phenomenological analogy to Anderson localization. Our findings are opposite to the common belief of the quasiparticle picture for the doped hole and unveil a completely new paradigm for lightly doped Mott insulators.
Effect of thermal fluctuations in topological p-wave superconductors

Bela Bauer
Microsoft Corporation
September 21, 2012

PIRSA:12090039
Condensed Matter
In this talk, I will present our recent work on the effect of thermal fluctuations on the topological stability of chiral p-wave superconductors. We consider two models of superconductors: spinless and spinful with a focus on topological properties and Majorana zero-energy modes. We show that proliferation of vortex-antivortex pairs above the Kosterlitz-Thouless temperature T_KT drives the transition from a thermal Quantum Hall insulator to a thermal metal/insulator, and dramatically modifies the ground-state degeneracy splitting. This shows that in order to utilize 2D chiral p-wave superconductors for topological quantum computing, the temperature should be much smaller than T_KT. Within the spinful chiral p-wave model, we also investigate the interplay between half-quantum vortices carrying Majorana zero-energy modes and full-quantum vortices having trivial topological charge, and discuss topological properties of half-quantum vortices in the background of proliferating full-quantum vortices.
Hamiltonian Theory of Fractional Chern Bands

Ramamurti Shankar
Yale University
September 14, 2012

PIRSA:12090047
Mathematical physics
It has been known for some time that a system with a filled band will have an integer quantum Hall conductance equal to its Chern number, a toplogical index associated with the band. While this is true for a system in a magnetic field with filled Landau Levels, even a system in zero external field can exhibit the QHE if its band has a Chern number. I review this issue and discuss a more recent question of whether a partially filled Chern band can exhibit the Fractional QHE. I describe the work done with Ganpathy Murthy in which we show how composite fermions, which were so useful in explaining the usual FQHE, can be introduced here and with equal success by adapting our Hamiltonian Theory of CFs developed for the FQHE in the continuum.
Charge fractionalization and entanglement entropy for compressible phases in holography

Liza Huijse
Karius, Inc.
September 11, 2012

PIRSA:12090059
Condensed Matter
Multiplets in the Entanglement Spectrum

Ari Turner
Universiteit van Amsterdam

September 06, 2012

PIRSA:12090056

What information can be determined about a state given just the ground state wave function? Quantum ground states, speaking intuitively, contain fluctuations between many of the configurations one might want to understand. The information about them can be organized by introducing an imaginary system, dubbed the entanglement Hamiltonian. What light does the dynamics of this Hamiltonian (a precise version of the notion of "zero point motion") shed on the actual system?

I will start my discussion near critical points, where Lorentz invariance often emerges and the entanglement Hamiltonian becomes tractable, revealing that it exists in one dimension less than the real system. One application is to the fluctuations of angular momentum in a spin chain.

The entanglement Hamiltonian is especially successful at clarifying the properties of quantum phases without order, such as topological insulators. In particular, spin chains often have no long range order due to quantum fluctuations. Nevertheless there can be phase transitions between two of these disordered states, suggesting the existence of a hidden order.

My main aim in the talk will be to demonstrate that the entanglement spectrum can serve as an order parameter for these unusual transitions; this observation leads to a classification of one-dimensional phases. One can understand the phases of the actual system simply by looking at the spectrum of the entanglement Hamiltonian, just as one deduces the properties of atoms from their spectra.
Topological Order in Spin Systems

Paul Fendley
University of Oxford
August 10, 2012

PIRSA:12080002
Particle Physics
Much effort has been devoted to the study of systems with topological order, motivated by practical issues as well as more field theoretical and mathematical concerns. This talk will give an overview of some of the field, describing abelian systems relevant to the search for spin liquids, and non-abelian systems relevant to topological quantum computation. I will focus in particular on problems not reducible to free-fermion ones; examples include the RVB state of electrons as well as models of quantum loops and nets.
Glass: The Cinderella Problem of Condensed Matter Physics

Anthony Leggett
University of Illinois Urbana-Champaign
August 03, 2012

PIRSA:12080001
Condensed Matter
Amorphous materials (glasses) probably constitute >90% of the solid matter surrounding us in everyday life,yet traditional textbooks of condensed matter physics devote virtually no space to them.Crudely speaking,the puzzles in the behavior of glasses can be divided into three major areas:the glass transition itself,the characteristic long-term memory effects and the near-equilibrium thermal,dielectric and transport properties;this talk focusses entirely on the third area.Over the last 40 years it has become apparent that the thermal and transport properties are not only qualitatively universal between glasses with totally different chemistry and microstructure,but in some cases possess a truly mind-boggling degree of _quantitative_ universality.In this talk I will describe the salient experimental data,review the established ("tunnelling two-level system") model commonly used to interpret them,and introduce a rather different scenario (developed in collaboration with D.C.Vural) which holds out some prospect of explaining the universalities in a natural way.
Integer Quantum Hall Effect for Bosons: A Physical Realization

Senthil Todadri
Massachusetts Institute of Technology (MIT) - Department of Physics
July 27, 2012

PIRSA:12070013
Condensed Matter
A simple physical realization of an integer quantum Hall state of interacting two dimensional bosons is provided. This is an example of a "symmetry-protected topological" (SPT) phase which is a generalization of the concept of topological insulators to systems of interacting bosons or fermions. Universal physical properties of the boson integer quantum Hall state are described and shown to correspond to those expected from general classifications of SPT phases.
Symmetry Protected Topological Phases; from Quantum Entanglement to Interaction Effects

Ashvin Vishwanath
Harvard University
July 27, 2012

PIRSA:12070012
Condensed Matter
I will briefly review topological phases of non interacting fermions, such as topological insulators, and discuss how ideas from quantum information, in particular the entanglement spectrum, can be used to characterize them. For topological phases protected by inversion symmetry I argue that this is the ideal tool, and discuss how it leads to a classification of 3D topological phases. Next, I will discuss topological phases that only appear in the presence of interactions, although they share essential characteristics with non-interacting topological phases. A general theory of such states of bosons in 2+1 dimensions will be given, and specific examples, the bosonic analogs of topological superconductors and insulators, will be discussed.

Title	Speaker(s)	Date	Talk Type	Info
An Informal Discussion About Topological Gauge Theory, part 2	Xiao-Gang Wen	2012-10-30	Other	View details
Synthetic non-Abelian anyons in fractional Chern insulators and beyond	Xiaoliang Qi	2012-10-26	Scientific Series	View details
An informal discussion about topological gauge theory	Xiao-Gang Wen	2012-10-23	Scientific Series	View details
Self-localization of a single hole in Mott antiferromagnets	Zheng-Yu Weng	2012-10-19	Scientific Series	View details
Effect of thermal fluctuations in topological p-wave superconductors	Bela Bauer	2012-09-21	Scientific Series	View details
Hamiltonian Theory of Fractional Chern Bands	Ramamurti Shankar	2012-09-14	Scientific Series	View details
Charge fractionalization and entanglement entropy for compressible phases in holography	Liza Huijse	2012-09-11	Scientific Series	View details
Multiplets in the Entanglement Spectrum	Ari Turner	2012-09-06	Scientific Series	View details
Topological Order in Spin Systems	Paul Fendley	2012-08-10	Scientific Series	View details
Glass: The Cinderella Problem of Condensed Matter Physics	Anthony Leggett	2012-08-03	Scientific Series	View details
Integer Quantum Hall Effect for Bosons: A Physical Realization	Senthil Todadri	2012-07-27	Scientific Series	View details
Symmetry Protected Topological Phases; from Quantum Entanglement to Interaction Effects	Ashvin Vishwanath	2012-07-27	Scientific Series	View details

Quantum Matter

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