Generalized Bose-Einstein condensation into multiple states in driven-dissipative systems

TL;DR

This paper demonstrates that Bose-Einstein condensation can occur in driven-dissipative systems far from equilibrium, leading to the macroscopic occupation of multiple states rather than a single ground state.

Contribution

It introduces a generalized form of Bose-Einstein condensation involving multiple states in non-equilibrium systems and provides a mean-field criterion for state selection.

Findings

Bose-Einstein condensation persists in non-equilibrium steady states.

Multiple states can be simultaneously macroscopically occupied.

A proposed quantum switch controls heat conductivity by shifting between selected states.

Abstract

Bose-Einstein condensation, the macroscopic occupation of a single quantum state, appears in equilibrium quantum statistical mechanics and persists also in the hydrodynamic regime close to equilibrium. Here we show that even when a degenerate Bose gas is driven into a steady state far from equilibrium, where the notion of a single-particle ground state becomes meaningless, Bose-Einstein condensation survives in a generalized form: the unambiguous selection of an odd number of states acquiring large occupations. Within mean-field theory we derive a criterion for when a single and when multiple states are Bose selected in a non-interacting gas. We study the effect in several driven-dissipative model systems, and propose a quantum switch for heat conductivity based on shifting between one and three selected states.