Nonequilibrium states of a quenched Bose gas

Abstract

Yin and Radzihovsky [1] recently developed a self-consistent extension of a Bogoliubov theory, in which the condensate number density nc is treated as a mean field that changes with time, in order to analyze a JILA experiment by Makotyn et al.[2] on a 85 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 ofṅc, 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 theṅc-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.

Quench dynamics of a Bose-Einstein condensate under synthetic spin-orbit coupling

“…This treatment is equivalent to a self-consistent time-dependent Bogoliubov theory, which should provide a qualitatively correct picture when the condensate depletion is not too large. Similar approaches have been adopted to describe quench processes in BEC and Fermi systems [11,14,[16][17][18][22][23][24]. We note that our assumption here implies that θ is not time dependent.…”

“…While in our system the quasi-particle excitations are not isolated due to the existence of a condensate reservoir, we follow the argument first presented in Ref. [24], that in the long-time limit, the quasi-particle excitations are approximately constants of motion. Thus, the quasi-particles can be treated as an integrable system, and we may describe the system with the generalize Gibbs ensemble.…”

“…In the absence of SOC, it has been shown in Ref. [24] that the steady-state in the long-time limit can be well described by the generalized Gibbs ensemble with the Gibbs temperatures defined by…”

“…Following the standard practice, in a generalized Gibbs ensemble, the density operator is given as [24] …”

“…This allows the gas to evolve into a stead-state BEC. Theoretically, the quench process and the final steady-state properties can be qualitatively captured by dynamic mean field approaches [23,24].…”