Between Localization and Ergodicity in Quantum Systems

18.04.2016 17:00 – 19:00

Strictly speaking the laws of the conventional Statistical Physics, in particular the Equipartition Postulate, apply only in the presence of a thermostat. For a long time this restriction did not look crucial for realistic systems. Recently
there appeared two classes of quantum many-body systems with the coupling to the outside world that is (or is hoped to be) negligible: (1) cold quantum gases and (2) systems of qubits, which enjoy a continuous progress in their disentanglement from the environment. To describe such systems properly one should revisit the very foundations of the Statistical Mechanics. The first step in this direction was the development of the concept of Many-Body Localization: states of a many-body system can be localized in the Hilbert space resembling the celebrated Anderson Localization of single particle states in a random potential.

Localization implies that the state of the system decoupled from the thermostat depends on the initial conditions: the time averaging does not result in equipartition distribution, the entropy never reaches its thermodynamic value i.e. the ergodicity is violated. We will discuss evidences for the realization of delocalized non-ergodic systems and speculate about their properties, which
can’t be described in the conventional way.

Lieu

Bâtiment: Ecole de Physique

entrée libre