Condensed Matter

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Twisted quantum double model of topological phases

Yidun Wan Fudan University
November 21, 2012
PIRSA:12110079
Condensed Matter
Twisted quantum double model of topological phases

Yidun Wan Fudan University
November 21, 2012
PIRSA:12110077
Condensed Matter
Superradiant Superconductivity

Baskaran Ganapathy Institute of Mathematical Sciences
November 16, 2012
PIRSA:12110071
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
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

Twisted quantum double model of topological phases

Yidun Wan Fudan University
November 21, 2012
PIRSA:12110079
Condensed Matter
Twisted quantum double model of topological phases

Yidun Wan Fudan University
November 21, 2012
PIRSA:12110077
Condensed Matter
Superradiant Superconductivity

Baskaran Ganapathy Institute of Mathematical Sciences
November 16, 2012
PIRSA:12110071
Condensed Matter
In Dicke Superradiance, a collection of 2-level atoms interacting with a single boson mode acquires, through quantum coherence, an enhanced emission property and a rich dynamics. We suggest possibility of Dicke superradiance in a BCS superconductor. The necessary 2-level atoms are identified with Anderson pseudo spins seeing a self consistent mean field in k-space. A way to couple these 2-level bose atoms to an external boson mode and create a novel non equilibrium superradiant superconductivity (SRSC) is suggested. Our mechanism offers a hope to realize transient superconductivity, even at room temperatures, in the pseudo gap phase of certain underdoped cuprates. Recent experiments are briefly discussed in this light. Further SRSC exhibits interesting quantum entanglement and superfluorescence properties.
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.

Title	Speaker(s)	Date	Talk Type	Info
Twisted quantum double model of topological phases	Yidun Wan	2012-11-21	Scientific Series	View details
Twisted quantum double model of topological phases	Yidun Wan	2012-11-21	Other	View details
Superradiant Superconductivity	Baskaran Ganapathy	2012-11-16	Scientific Series	View details
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

Condensed Matter

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