Nonequilibrium states of a quenched Bose gas

Abstract

Yin and Radzihovsky [X. Yin and L. Radzihovsky, Phys. Rev. A 88, 063611 (2013)] recently developed a self-consistent extension of a Bogoliubov theory, in which the condensate number density ${n}_{c}$ is treated as a mean field that changes with time, in order to analyze a JILA experiment by Makotyn et al. [P. Makotyn et al., Nat. Phys. 10, 116 (2014)] on a $^{85}\mathrm{Rb}$ Bose gas following a deep quench to a large scattering length. We apply this theory to construct a closed set of equations that highlight the role of ${\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{n}}_{c}$, which is to induce an effective interaction between quasiparticles. We show analytically that such a system supports a steady state characterized by a constant condensate density and a steady but periodically changing momentum distribution, whose time average is described exactly by the generalized Gibbs ensemble. We discuss how the ${\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{n}}_{c}$-induced effective interaction, which cannot be ignored on the grounds of the adiabatic approximation for modes near the gapless Goldstone mode, can significantly affect condensate populations and Tan's contact for a Bose gas that has undergone a deep quench.