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A unification of symmetric Z2 spin liquids on kagome lattice

Yuan-Ming Lu

February 14, 2014 PIRSA:14020118
13/14 PSI - String Theory Review - Lecture 14

Davide Gaiotto Perimeter Institute for Theoretical Physics

February 14, 2014 PIRSA:14020034
Low Spin State Mott Insulators and Emergence of novel Quantum Spin Liquids

Baskaran Ganapathy The Institute of Mathematical Sciences - Chennai

February 14, 2014 PIRSA:14020128
13/14 PSI - Cosmology Review - Lecture 13

Latham Boyle Perimeter Institute for Theoretical Physics

February 14, 2014 PIRSA:14020102
Many-body localization with dipoles

Chris Laumann Boston University

February 14, 2014 PIRSA:14020129
Introduction to Effective Field Theories - Lecture 12

Cliff Burgess McMaster University

February 14, 2014 PIRSA:14020093
Quantum Walks and algorithmic speedup

Richard Cleve Institute for Quantum Computing (IQC)

November 24, 2004 PIRSA:04110038
13/14 PSI - Quantum Gravity Review - Lecture 1

Bianca Dittrich Perimeter Institute for Theoretical Physics

February 18, 2014 PIRSA:14020061
Evolution of cosmological black holes: exact solutions, accretion and scalar fields

Daniel Guariento Conestoga College
February 18, 2014 PIRSA:14020150
Cosmology
13/14 PSI - Quantum Information Review - Lecture 1

Andrew Childs University of Waterloo

February 18, 2014 PIRSA:14020072
Cluster Polylogarithms for Scattering Amplitudes
February 18, 2014 PIRSA:14020147
Quantum Fields and Strings
Psi-epistemic models are exponentially bad at explaining the distinguishability of quantum states

Matthew Leifer Chapman University
February 18, 2014 PIRSA:14020145
Quantum Foundations

A unification of symmetric Z2 spin liquids on kagome lattice

Yuan-Ming Lu

February 14, 2014 PIRSA:14020118

While there is mounting numerical evidence for a gapped Z2 spin liquid in the kagome Heisenberg model, a complete characterization of this topological phase remains to be accomplished. A defining property, the projective symmetry group (PSG) which fixes how the emergent excitations of the spin liquid phase transform under symmetry, remains to be determined. Following a Chern-Simons field theory, we show how PSG determines measurable properties of a Z2 spin liquid, such as the existence of symmetry protected gapless edge states. This fact enables us to unify two distinct types of projected wavefunctions for Z2 spin liquids: the Schwinger-boson states and the fermionic spinon states. We also provide concrete predictions for identifying the spin liquid ground state on the kagome lattice.
13/14 PSI - String Theory Review - Lecture 14

Davide Gaiotto Perimeter Institute for Theoretical Physics

February 14, 2014 PIRSA:14020034
Low Spin State Mott Insulators and Emergence of novel Quantum Spin Liquids

Baskaran Ganapathy The Institute of Mathematical Sciences - Chennai

February 14, 2014 PIRSA:14020128

In a conventional Mott insulator, magnitude of local spin moments remain fixed. They are `fixed spin Mott insulators'. We suggest that, in a multi orbital Hubbard model, when local Hund coupling is won over by inter-orbital superexchange couplings between neighboring sites, local spin moment can decrease its value in a cooperative fashion, through a first order phase transition, These are `Low spin state Mott insulators' (LSSMI). The minimal value of spins that can be reached are zero (half), for even (odd) number of electrons per site, We show that in LSSMI, depending on orbital degeneracy and electron number per site, novel quantum spin liquids can emerge, We discuss systems such as Fe arsenide, Fe selenide family and La2CoO3 in the light of our proposal. Certain long standing puzzles, including absence of any magnetic phase transition in La2CoO3 is explained in terms of a novel quantum spin liquid. Some properties of this spin liquid, a liquid of `quantum strings' will be discussed and some predictions made.
13/14 PSI - Cosmology Review - Lecture 13

Latham Boyle Perimeter Institute for Theoretical Physics

February 14, 2014 PIRSA:14020102
Many-body localization with dipoles

Chris Laumann Boston University

February 14, 2014 PIRSA:14020129

Statistical mechanics is the framework that connects thermodynamics to the microscopic world. It hinges on the assumption of equilibration; when equilibration fails, so does much of our understanding. In isolated quantum systems, this breakdown is captured by the phenomenon known as many-body localization. This breakdown manifests in a variety of ways, as elucidated by much recent theoretical and numerical work. Many-body localized phases violate Ohm's law and Fourier's law as they conduct neither charge nor heat; they can exhibit symmetry breaking and/or topological orders in dimensions normally forbidden by Mermin-Wagner arguments; they hold potential as strongly interacting quantum computers due to the slow decay of local coherence.
In this talk, I will briefly introduce the basic phenomena of many-body localization and review its theoretical status. To date, none of these phenomena has been observed in an experimental system, in part because of the isolation required to avoid thermalization. I will consider several dipolar systems which we believe to be ideal platforms for the realization of MBL phases and for investigating the associated delocalization phase transition. The presence of strong interactions in these systems underlies their potential for exploring physics beyond that of single particle Anderson localization. However, the power law of the dipolar interaction immediately raises the question: can localization in real space persist in the presence of such long-range interactions?
I will review and extend several arguments producing criteria for localization in the presence of power laws and present small-scale numerics regarding the MBL transition in several of the proposed dipolar systems.
Associated preprint:
N. Yao, CRL, S. Gopalakrishnan, M. Knap, M. Mueller, E. Demler., M. Lukin arXiv:1311.7151
Introduction to Effective Field Theories - Lecture 12

Cliff Burgess McMaster University

February 14, 2014 PIRSA:14020093
Quantum Walks and algorithmic speedup

Richard Cleve Institute for Quantum Computing (IQC)

November 24, 2004 PIRSA:04110038
13/14 PSI - Quantum Gravity Review - Lecture 1

Bianca Dittrich Perimeter Institute for Theoretical Physics

February 18, 2014 PIRSA:14020061
Evolution of cosmological black holes: exact solutions, accretion and scalar fields

Daniel Guariento Conestoga College
February 18, 2014 PIRSA:14020150
Cosmology
Systems which contemplate the gravitational interaction between compact objects and the matter content in a cosmological environment constitute an important problem which has been studied since the early days of General Relativity. The generalized McVittie black hole is a simple exact solution to this problem, which provides us with insight on some of its known physical aspects, as well as hints to new mechanisms which arise from a formal treatment. We review some properties of this solution and its matter source, which can be interpreted as a classical fluid but is also an exact solution to a nontrivial scalar field theory.
13/14 PSI - Quantum Information Review - Lecture 1

Andrew Childs University of Waterloo

February 18, 2014 PIRSA:14020072
Cluster Polylogarithms for Scattering Amplitudes
February 18, 2014 PIRSA:14020147
Quantum Fields and Strings
Motivated by the cluster structure of two-loop scattering amplitudes in N = 4 Yang-Mills theory we define cluster polylogarithm functions. We find that all such functions of weight 4 are made up of a single simple building block associated to the A2 cluster algebra. Adding the requirement of locality on generalized Stasheff polytopes, we find that these A2 building blocks arrange themselves to form a unique function associated to the A3 cluster algebra. ThisA3 function manifests all of the cluster algebraic structure of the two-loop n-particle MHV amplitudes for all n, and we use it to provide an explicit representation for the most complicated part of the n = 7 amplitude as an example.
Psi-epistemic models are exponentially bad at explaining the distinguishability of quantum states

Matthew Leifer Chapman University
February 18, 2014 PIRSA:14020145
Quantum Foundations
The status of the quantum state is perhaps the most controversial issue in the foundations of quantum theory. Is it an epistemic state (representing knowledge, information, or belief) or an ontic state (a direct reflection of reality)? In the ontological models framework, quantum states correspond to probability measures over more fundamental states of reality. The quantum state is then ontic if every pair of pure states corresponds to a pair of measures that do not overlap, and is otherwise epistemic. Recently, several authors have derived theorems that aim to show that the quantum state must be ontic in this framework. Each of these theorems involve auxiliary assumptions of varying degrees of plausibility. Without such assumptions, it has been shown that models exist in which the quantum state is epistemic. However, the definition of an epistemic quantum state used in these works is extremely permissive. Only two quantum states need correspond to overlapping measures and furthermore the amount of overlap may be arbitrarily small. In order to provide an explanation of quantum phenomena such as no-cloning and the indistinguishability of pure states, the amount of overlap should be comparable to the inner product of the quantum states. In this talk, I show, without making auxiliary assumptions, that the ratio of overlap to inner product must go to zero exponentially in Hilbert space dimension for some families of states. This is done by connecting the overlap to Kochen-Specker noncontextuality, from which we infer that any contextuality inequality gives a bound on the ratio of overlap to inner product.

Title	Speaker(s)	Date	Collection	Type	Info	Relevance
A unification of symmetric Z2 spin liquids on kagome lattice	Yuan-Ming Lu	2014‑02‑14	Emergence in Complex Systems	Conference	View details	1
13/14 PSI - String Theory Review - Lecture 14	Davide Gaiotto	2014‑02‑14	13/14 PSI - String Theory Review	Course	View details	1
Low Spin State Mott Insulators and Emergence of novel Quantum Spin Liquids	Baskaran Ganapathy	2014‑02‑14	Emergence in Complex Systems	Conference	View details	1
13/14 PSI - Cosmology Review - Lecture 13	Latham Boyle	2014‑02‑14	13/14 PSI - Cosmology Review	Course	View details	1
Many-body localization with dipoles	Chris Laumann	2014‑02‑14	Emergence in Complex Systems	Conference	View details	1
Introduction to Effective Field Theories - Lecture 12	Cliff Burgess	2014‑02‑14	Introduction to Effective Field Theories	Course	View details	1
Quantum Walks and algorithmic speedup	Richard Cleve	2004‑11‑24		Scientific Series	View details	1
13/14 PSI - Quantum Gravity Review - Lecture 1	Bianca Dittrich	2014‑02‑18	13/14 PSI - Quantum Gravity Review	Course	View details	1
Evolution of cosmological black holes: exact solutions, accretion and scalar fields	Daniel Guariento	2014‑02‑18	Cosmology and Gravitation	Scientific Series	View details	1
13/14 PSI - Quantum Information Review - Lecture 1	Andrew Childs	2014‑02‑18	13/14 PSI - Quantum Information Review	Course	View details	1
Cluster Polylogarithms for Scattering Amplitudes		2014‑02‑18	Quantum Fields and Strings	Scientific Series	View details	1
Psi-epistemic models are exponentially bad at explaining the distinguishability of quantum states	Matthew Leifer	2014‑02‑18	Quantum Foundations	Scientific Series	View details	1

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