Surprises from quenches in long-range interacting systems: Temperature inversion and cooling

TL;DR

This paper investigates the effects of sudden parameter changes (quenches) in long-range interacting systems, revealing phenomena like temperature inversion and proposing cooling methods, supported by extensive simulations and potential experimental relevance.

Contribution

It demonstrates the ubiquity of temperature inversion after quenches in long-range systems and introduces a novel cooling procedure based on iterative quenches and particle filtering.

Findings

Temperature inversion occurs after quenches in long-range systems.

A cooling method using iterative quenches and filtering is proposed.

Temperature inversion observed in natural astrophysical phenomena.

Abstract

What happens when one of the parameters governing the dynamics of a long-range interacting system of particles in thermal equilibrium is abruptly changed (quenched) to a different value? While a short-range system, under the same conditions, will relax in time to a new thermal equilibrium with a uniform temperature across the system, a long-range system shows a fast relaxation to a nonequilibrium {\em quasistationary state} (QSS). The lifetime of such an off-equilibrium state diverges with the system size, and the temperature is non-uniform across the system. Quite surprisingly, the density profile in the QSS obtained after the quench is anticorrelated with the temperature profile in space, thus exhibiting the phenomenon of {\em temperature inversion}: denser regions are colder than sparser ones. We illustrate with extensive molecular dynamics simulations the ubiquity of this scenario in a prototypical long-range interacting system subject to a variety of quenching protocols, and in a model that mimics an experimental setup of atoms interacting with light in an optical cavity. We further demonstrate how a procedure of iterative quenching combined with filtering out the high-energy particles in the system may be employed to cool the system. Temperature inversion is observed in nature in some astrophysical settings; our results imply that such a phenomenon should be observable, and could even be exploitable to advantage, also in controlled laboratory experiments.