Violent relaxation in quantum fluids with long-range interactions

TL;DR

This paper extends the concept of violent relaxation to quantum fluids with long-range interactions, using a quantum Hamiltonian Mean Field model and revealing quantum effects like interference and zero-point motion that influence relaxation dynamics.

Contribution

It develops a quantum version of the HMF model to study violent relaxation, highlighting quantum interference effects and suppression of relaxation by zero-point motion.

Findings

Quantum interference regulates caustic formation during relaxation.

Zero-point motion suppresses violent relaxation in the deep quantum regime.

Emergent length and time scales arise from quantum effects.

Abstract

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 quasi-stationary states that fall outside the standard paradigm of statistical mechanics. Violent relaxation was originally identified in gravity-driven stellar dynamics; here we extend the theory 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. We show that singular caustics that form during violent relaxation are regulated by interference effects in a universal way described by Thom's catastrophe theory applied to waves and this leads to emergent length and time scales not present in the classical problem. In the deep quantum regime we find that violent relaxation is suppressed altogether by quantum zero-point motion. Our results are relevant to laboratory studies of self-organization in cold atomic gases with long-range interactions.