Physics Colloquium

Prof. Andrew Potter, UT-Austin

"Quantum coherence in 'hot' matter"

4:00pm, The John A. Wheeler Lecture Hall (RLM 4.102). Coffee and cookies will be served at 3:45pm in RLM 4.102

Abstract: The traditional assumptions of ergodicity and chaos underpinning thermodynamics and statistical mechanics predict that, when excited away from their zero temperature ground-state, quantum systems with many degrees of freedom will relax to thermal equilibrium or "thermalize". Along the way, any quantum information encoded in the initial configuration becomes rapidly and irretrievably "scrambled", resulting in incoherent (classical) behavior at long times.

Recently, these deep-seated assumptions have been called into question. I will explain how strong randomness or "disorder" can prevent ergodicity and thermalization, via a phenomena called many body localization (MBL). In sharp contrast to conventional thermalizing systems, MBL systems exhibit quantum coherent dynamics indefinitely, even at arbitrarily high energy densities. This raises the enticing prospect of creating quantum phases of matter in "hot" matter, and also of engineering entirely new dynamical phases that simply could not exist in thermal equilibrium.

I will describe recent experimental progress in testing the ideas of MBL systems in cold atom and trapped ion systems, highlighting the first experimental realization of a dynamical quantum phase of matter in an MBL systems -- a discrete "time-crystal", a non-equilibrium phase of matter that spontaneously breaks time-translation symmetry.