Le contenu de cette page n’est pas disponible en français. Veuillez nous en excuser.

# Condensed Matter

This series consists of talks in the area of Condensed Matter.

## Seminar Series Events/Videos

Currently there are no upcoming talks in this series.

## The mother of all states of the kagome quantum antiferromagnet

Lundi juin 19, 2017

Frustrated magnets provide a fertile ground for discovering exotic states of matter, such as those with topologically non-trivial properties. Motivated by several near-ideal material realizations, we focus on aspects of the two-dimensional kagome antiferromagnet. I present two of our works in this area both involving the spin-1/2 XXZ antiferromagnetic Heisenberg model. First, guided by a previous field theoretical study, we explore the XY limit ($J_z=0$) for the case of 2/3 magnetization (i.e.

Collection/Series:
Scientific Areas:

## Spectrum of conformal gauge theories on a torus

Vendredi juin 16, 2017
Speaker(s):

Many model quantum spin systems have been proposed to realize critical points or phases described by 2+1 dimensional conformal gauge theories. On a torus of size L and modular parameter τ, the energy levels of such gauge theories equal (1/L) times universal functions of τ. We compute the universal spectrum of QED3, a U(1) gauge theory with Nf two-component massless Dirac fermions, in the large-Nf limit.

Collection/Series:
Scientific Areas:

## Many-Body Localization Through the Lens of Ultracold Quantum Gases

Mardi mai 23, 2017
Speaker(s):

A fundamental assumption of quantum statistical mechanics is that closed isolated systems always thermalize under their own dynamics. Progress on the topic of many-body localization has challenged this vital assumption, describing a phase where thermalization, and with it, equilibrium thermodynamics, breaks down.

Collection/Series:
Scientific Areas:

## Z_2 topological order near the Neel state of the square lattice antiferromagnet

Jeudi mai 18, 2017
Speaker(s):

We classify quantum states proximate to the semiclassical Neel state of the spin S=1/2 square lattice antiferromagnet with two-spin near-neighbor and four-spin ring exchange interactions. Motivated by a number of recent experiments on the cuprates and the iridates, we examine states with Z_2 topological order, an order which is not present in the semiclassical limit. Some of the states break one or more of reflection, time-reversal, and lattice rotation symmetries, and can account for the observations. We discuss implications for the pseudogap phase.

Collection/Series:
Scientific Areas:

## Estimating entanglement from only a few moments

Mardi mai 09, 2017
Speaker(s):

How can we quantify the entanglement between subsystems when we only have access to incomplete information about them and their environment?‎ Existing approaches (such as Rényi entropies) can only detect the short-range entanglement across a boundary between a subsystem and its surroundings, and then only if the whole system is pure. These methods cannot detect the long-range entanglement between two subsystems embedded in a larger system.

Collection/Series:
Scientific Areas:

## Resonating valence bond theory of the spin-1/2 kagome Heisenberg antiferromagnet

Mardi avr 18, 2017

Recent studies of highly frustrated antiferromagnets (AFMs) have demonstrated the qualitative impact of virtual, longer-range singlet excitations on the effective RVB tunneling parameters of the low energy sector of the problem [1,2]. Here, I will discuss the current state of affairs on the RVB description of the spin-1/2 kagome AFM, and present new results that settle a number of issues in this problem [3].

[1] I. Rousochatzakis, Y. Wan, O. Tchernyshyov, and F. Mila, PRB 90,

100406(R) (2014)

Collection/Series:
Scientific Areas:

## Random variables, entanglement and nonlocality in infinite > translation-invariant systems

Mardi avr 11, 2017

We consider the problem of certifying entanglement and nonlocality in one-dimensional translation-invariant (TI) infinite systems when just averaged near-neighbor correlators are available. Exploiting the triviality of the marginal problem for 1D TI distributions, we arrive at a practical characterization of the near-neighbor density matrices of multi-separable TI quantum states. This allows us, e.g., to identify a family of separable two-qubit states which only admit entangled TI extensions.

Collection/Series:
Scientific Areas:

## SU(3) Landau-Zener-Stueckelberg-Majorana interferometry with quantum triangles

Mardi avr 04, 2017
Speaker(s):

Quantum triangles can work as interferometers. Depending on their geometric size and interactions between paths, “beats” and/or “steps”

Collection/Series:
Scientific Areas:

## Exposing the Global Landscape of Topological Quantum Matter

Mardi mar 28, 2017
Speaker(s):

A central theme of modern condensed matter physics is the study of topological quantum matter enabled by quantum mechanics, which provides a further "topological" twist to the classical theory of ordered phases.

Collection/Series:
Scientific Areas:

## Mesonic eigenstates for magnetic monopoles in quantum spin ice

Mardi mar 21, 2017
Speaker(s):

The quest for quantum spin liquids is an important enterprise in strongly correlated physics, yet candidate materials are still few and far between. Meanwhile, the classical front has had far more success, epitomized by the exceptional agreement between theory and experiment for a class of materials called spin ices. It is therefore natural to introduce quantum fluctuations into this well-established classical spin liquid model, in the hopes of obtaining a fully quantum spin liquid state.

Collection/Series:
Scientific Areas:

## LECTURES ON-DEMAND

### Roger Melko: Perimeter Institute and University of Waterloo

Speaker: Roger Melko