A superheated Bose-condensed gas

TL;DR

This paper demonstrates the creation of a superheated Bose-Einstein condensate that persists above the equilibrium critical temperature due to reduced coupling with the thermal bath, revealing non-equilibrium phase transition phenomena.

Contribution

It introduces a method to create and analyze a superheated BEC by tuning interatomic interactions, highlighting non-equilibrium effects on phase transitions.

Findings

Superheated BEC persists above $T_c$ when interactions are reduced.

Rapid boiling occurs when strong interactions are suddenly introduced.

A non-equilibrium phase diagram is reconstructed and theoretically modeled.

Abstract

Our understanding of various states of matter usually relies on the assumption of thermodynamic equilibrium. However, the transitions between different phases of matter can be strongly affected by non-equilibrium phenomena. Here we demonstrate and explain an example of non-equilibrium stalling of a continuous, second-order phase transition. We create a superheated atomic Bose gas, in which a Bose-Einstein condensate (BEC) persists above the equilibrium critical temperature, $T_c$, if its coupling to the surrounding thermal bath is reduced by tuning interatomic interactions. For vanishing interactions the BEC persists in the superheated regime for a minute. However, if strong interactions are suddenly turned on, it rapidly "boils" away. Our observations can be understood within a two-fluid picture, treating the condensed and thermal components of the gas as separate equilibrium systems with a tuneable inter-component coupling. We experimentally reconstruct a non-equilibrium phase diagram of our gas, and theoretically reproduce its main features.