Quantum Cafe: Ehud Altman

Quantum Café is CCQ’s ongoing seminar series: open to all bona fide members of the greater NYC scientific community and held every second week, Quantum Café presents a series of informal, highly interactive talks, typically by external speakers, which present the most interesting recent developments and open questions in our field.

Title: Computing Quantum Thermalization Dynamics: From Quantum Chaos to Emergent Hydrodynamics

Abstract: Computing the dynamics of strongly interacting quantum systems presents a fundamental challenge due to the growth of entanglement entropy in time. In the first part of the talk I will describe a new approach that overcomes this obstruction and captures chaotic dynamics and emergent hydrodynamic transport of quantum systems. Our scheme utilizes the time dependent variational principle with matrix product states to truncate “non-useful” entanglement, while retaining crucial information on local observables. In the second part of the talk I will offer a new viewpoint on the relation between quantum and classical chaos in many body systems, using a classical version of the Sachdev-Ye-Kitaev model as an example. Chaos in this model can be understood as arising from diverging geodesics on a SO(N) manifold equipped with a random metric with locally negative curvature. The quantum bound on chaos arises from a “chaotic mobility edge” in the classical Lyapunov spectrum, separating the lower part of the spectrum for which a classical chaos picture applies from the higher part of the spectrum for which quantum interference effects are strong enough to kill classical chaos. This edge corresponds to a curvature scale of the order of the de Broglie wavelength.