Dartmouth Events

Abstract: Both our everyday experience and laboratory experiments indicate that physical systems, initially
prepared in a non-equilibrium state, time-evolve into thermal equilibrium. Sets of axioms have
been formulated to justify this generic behavior and the emergence of statistical mechanics. Yet,
there is no clear understanding of the fundamental principles underlying the universality of
thermalization and ergodicity. How do such irreversible thermal states emerge in quantum
systems, which are governed by the “reversable” unitary laws of quantum physics?
This talk will review recent work on this topic and the closely related field of many-body
quantum chaos. It will first introduce the basic notions of classical and quantum chaos in single-
particle systems. We will consider different facets of quantum chaoticity such as universal
distribution of energy levels and the quantum butterfly effect. Then, the concept of many-body
quantum chaos will be defined using the former approach rooted in celebrated random matrix
theory. It will be briefly discussed how this theory can be derived from first principles, which
will lead to a surprising observation that small non-unitary perturbations strongly affect the
resulting theory. It suggests the key conclusion of our recent work that spontaneous breaking of
unitarity may be responsible for the emergence of chaos in interacting many-body systems.

Hosted by Professor Rufus Boyack