Fluctuations in out-of-equilibrium Bose gases

Fluctuations in thermodynamic quantities are well understood for systems in thermal equilibrium and reveal important macroscopic properties of the system via fluctuation-dissipation relations. Extending such descriptions to out-of-equilibrium systems is an open problem. Ultracold atomic systems provide an ideal setting for testing theories of out-of-equilibrium physics owing to their isolation from the environment and the ability to control equilibration timescales via Feshbach resonances. Using both non-interacting and weakly interacting ultracold 39K gases trapped in a cylindrical box, we study how driving the system far from equilibrium increases momentum-space fluctuations compared to equilibrium Bose gases.