# Quantum Encounters Seminar

## Quantum Information, Condensed Matter, Quantum Field Theory

A seminar organized by Vasily Pestun and Slava Rychkov

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# Quantum Encounters Seminar

## Quantum Information, Condensed Matter, Quantum Field Theory

### Schedule

#### 18th October, 2021 - 04:10:00 Adam Nahum (ENS Paris)

### TBA

#### 5th October, 2021 - 04:10:00 Yoshiko Ogata (Univ. Tokyo)

### TBA

#### 1st June, 2021 - 04:06:00 Peter C.W. Holdsworth (Ecole Normale Supérieure de Lyon)

### Emergence: from spins to charges

#### 27th April, 2021 - 05:04:00 Anton Kapustin (Caltech)

### Noncommutative Geometry of Quantum Lattice Models and the Higher Berry Phase

A seminar organized by Vasily Pestun and Slava Rychkov

18th Oct, 2021 | Adam Nahum | TBA | ||

5th Oct, 2021 | Yoshiko Ogata | TBA | ||

1st Jun, 2021 | Peter C.W. Holdsworth | Emergence: from spins to charges | ||

27th Apr, 2021 | Anton Kapustin | Noncommutative Geometry of Quantum Lattice Models and the Higher Berry Phase |

Emergence is a major buzz word of our times. My working definition, which gives plenty of room for manoeuvre is: the appearance of many body phenomena of higher symmetry than that of the Hamiltonian and degrees of freedom at the microscopic level.

In this colloquium I will discuss a topical example - the frustrated magnetic material, spin ice. Here, to an excellent approximation a classical field theoretic description with continuous U(1) symmetry emerges from Ising like degrees of freedom. The associated quasi-particles appear to be freely moving magnetic charge - magnetic monopoles - and the system behaves as a magnetic Coulomb fluid in the grand canonical ensemble with intrinsic topological properties. With the addition of quantum fluctuations the emergent magneto-statics develops further into a complete analogue of quantum electrodynamics. I will aliment this discussion with experimental results from a wide range of systems.

https://us02web.zoom.us/j/85270888147?pwd=aXdOVXBTSmNEU00vVFE2bXhqdE5vdz09

ID de réunion : 852 7088 8147

Code secret : 276852

Recently methods of quantum statistical mechanics have been fruitfully applied to the study of phases of quantum lattice systems at zero temperature. For example, a rigorous definition of a Short-Range Entangled phase of matter has been given and a classification of such phases in one spatial dimension has been achieved. I will discuss some of these developments, focusing on the topology and geometry of the space of Short-Range Entangled states. According to a conjecture of A. Kitaev, these spaces form a loop spectrum in the sense of homotopy theory. This conjecture implies that to any family of Short-Range entangled states in one dimension one can associate a gerbe on the parameter space. I will show how to construct such a gerbe. Thе curvature of this gerbe is a closed 3-form with quantized periods and can be regarded as a higher-dimensional generalization of the curvature of the Berry connection.

https://us02web.zoom.us/j/81778962715?pwd=QnpNS2ErSnBCTWRYUHphd1VMMysyZz09

ID de réunion : 817 7896 2715

Code secret : 800452