Friday, 2^nd of October 2020 at 12:00
meet.google.com/qdf-kcuo-myh

Duncan O’Dell

Department of Physics and Astronomy, McMaster University
“Violent relaxation in quantum fluids
with long-range interactions”

Violent relaxation is a process that occurs in systems with long-range interactions. It has the peculiar feature of dramatically amplifying small perturbations, and rather than driving the system to equilibrium, it instead leads to slowly evolving configurations known as quasistationary states that fall outside the standard paradigm of statistical mechanics. Violent relaxation was originally identified in gravity-driven stellar dynamics; here, I will discuss its extension into the quantum regime by developing a quantum version of the Hamiltonian mean field (HMF) model which exemplifies many of the generic properties of long-range interacting systems. The HMF model can either be viewed as describing particles interacting via a cosine potential, or equivalently as the kinetic XY model with infinite-range interactions, and its quantum fluid dynamics can be obtained from a generalized Gross-Pitaevskii equation.

I will also show that singular caustics that form during violent relaxation in the classical model are regulated by interference effects in a universal way described by Thom’s catastrophe theory applied to waves and this leads to emergent length scales and timescales not present in the classical problem. In the deep quantum regime we find that violent relaxation is suppressed altogether by quantum zero-point motion. If time permits I will also discuss soliton solutions of the HMF model. These results are relevant to laboratory studies of self-organization in cold atomic gases with long-range interactions.