The new physics of non-equilibrium condensates: insights from classical dynamics

TL;DR

This paper explores the dynamics of non-equilibrium classical condensates, revealing how coherent states can form and persist without dissipation through simulations of Dicke-type models, highlighting mechanisms like instabilities and inhomogeneous broadening.

Contribution

It introduces a detailed analysis of classical Dicke models showing spontaneous coherence and persistent oscillations, extending understanding of non-equilibrium condensate dynamics beyond dissipative systems.

Findings

Spontaneous coherent states with persistent oscillations can develop in undamped models.

Randomness in couplings suppresses oscillations, leading to stable, time-independent order parameters.

Non-equilibrium polariton condensates can form without dissipation through dynamical instabilities.

Abstract

We discuss the dynamics of classical Dicke-type models, aiming to clarify the mechanisms by which coherent states could develop in potentially non-equilibrium systems such as semiconductor microcavities. We present simulations of an undamped model which show spontaneous coherent states with persistent oscillations in the magnitude of the order parameter. These states are generalisations of superradiant ringing to the case of inhomogeneous broadening. They correspond to the persistent gap oscillations proposed in fermionic atomic condensates, and arise from a variety of initial conditions. We show that introducing randomness into the couplings can suppress the oscillations, leading to a limiting dynamics with a time-independent order parameter. This demonstrates that non-equilibrium generalisations of polariton condensates can be created even without dissipation. We explain the dynamical origins of the coherence in terms of instabilities of the normal state, and consider how it can additionally develop through scattering and dissipation.