Quantum Encounters Seminar

Quantum Information, Condensed Matter, Quantum Field Theory

A seminar organized by Vasily Pestun and Slava Rychkov


18th Oct, 2021Adam Nahum TBA
5th Oct, 2021Yoshiko Ogata TBA
1st Jun, 2021Peter C.W. Holdsworth Emergence: from spins to charges
27th Apr, 2021Anton Kapustin Noncommutative Geometry of Quantum Lattice Models and the Higher Berry Phase

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


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


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

Emergence: from spins to charges

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.


ID de réunion : 852 7088 8147
Code secret : 276852

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

Noncommutative Geometry of Quantum Lattice Models and the Higher Berry Phase

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.


ID de réunion : 817 7896 2715
Code secret : 800452