Quantum Matter

Displaying 373 - 384 of 436

Entanglement and the Fermi surface

Brian Swingle Brandeis University
November 27, 2012

PIRSA:12110082
Condensed Matter
Exact Calculations in the 1D Continuum for DFT and Beyond

November 27, 2012

PIRSA:12110085
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

Entanglement and the Fermi surface

Brian Swingle Brandeis University
November 27, 2012

PIRSA:12110082
Condensed Matter
In this talk I will describe my work characterizing quantum entanglement in systems with a Fermi surface. This class includes everything from Fermi liquids to exotic spin liquids in frustrated magnets and perhaps even holographic systems. I review my original scaling argument and then describe in detail a number of new precise results on entanglement in Fermi liquids. I will also discuss recent quantum Monte Carlo calculations of Renyi entropies and will argue that we now have a rather complete agreement between theory and numerics for Fermi liquid entanglement. I will also discuss universal crossovers between thermal and entanglement entropy and a class of solvable interacting models where we can prove the universality of the Widom formula for Fermi surface entanglement. If there is time, I will comment on several other topics including fluctuations of conserved quantities and connections to holography.
Exact Calculations in the 1D Continuum for DFT and Beyond

November 27, 2012

PIRSA:12110085

Most applications of the density matrix renormalization group (DMRG) have been to lattice models with short range interactions. But recent developments in DMRG technology open the door to studying continuum systems with long-range interactions in one dimension (1d). One key motivation is simulating cold atom experiments, where it is possible to engineer Hamiltonians of precisely this type. We have been applying DMRG in the 1d continuum with another motivation: to investigate and improve density functional theory (DFT). DFT has exact mathematical foundations, but in practice one must use approximations. These approximations work incredibly well for weakly correlated systems yet fail when correlations are strong. Improving DFT directly for realistic 3d systems is hard because few systems can be solved exactly. By working in the 1d continuum instead, we can use the power of DMRG to study DFT. We can implement both the exact DFT formalism and standard DFT approximations. After showing how to overcome the challenges in performing these calculations, I will discuss some of the key questions we are investigating, for example, the ability of DFT to predict gaps of insulating systems.
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

Title	Speaker(s)	Date	Talk Type	Info
Entanglement and the Fermi surface	Brian Swingle	2012-11-27	Scientific Series	View details
Exact Calculations in the 1D Continuum for DFT and Beyond		2012-11-27	Scientific Series	View details
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

Quantum Matter

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