Quench dynamics of a strongly interacting resonant Bose gas

We explore the dynamics of a Bose gas following its quench to a strongly interacting regime near a Feshbach resonance. Within a self-consistent Bogoliubov analysis we find that after the initial condensate-quasiparticle Rabi oscillations, at long time scales the gas is characterized by a nonequilibrium steady-state momentum distribution function, with depletion, condensate density, and contact that deviate strongly from their corresponding equilibrium values. These are in a qualitative agreement with recent experiments on ${}^{85}$Rb by Makotyn et al. Our analysis also suggests that for sufficiently deep quenches close to the resonance the nonequilibrium state undergoes a phase transition to a fully depleted state, characterized by a vanishing condensate density.

Figure 1

Time evolution of the (column-density) momentum distribution function ${\tilde{n}}_{{\mathbf{k}}_{\perp }}\left(t\right)\equiv n^{-1/3}{V}^{-1}\int d{k}_z{n}_{\mathbf{k}}\left(t\right)$ following a scattering length quench $k_n{a}_0=0.01\to k_n{a}_f=0.6$ in a resonant Bose gas.

Figure 2

A nonequilibrium steady-state momentum distribution function $n_k^{\infty }$, approached at long times, following a scattering length quench $a_0\to a_f$ (illustrated for $k_n{a}_f=0.1,0.2,\cdots ,0.9$ and $k_n{a}_0=0.01$) in a resonant Bose gas. The inset illustrates the presence of the $1/k^4$ large momentum tail.

Figure 3

Time evolution of the condensate depletion $n_d\left(t\right)$ as a function of pulse duration $t$, following a scattering length quench $a_0\to a_f$ in a resonant Bose gas. The inset shows an approximate collapse of the scaled depletion, with only a weak dependence on other parameters.

Figure 4

Long-time condensate fraction $n_c$ as a function of interaction strength $k_n{a}_f$. For a sufficiently deep quench, $k_n{a}_f>1.35$ (for $k_n{a}_0=0.01$), the asymptotic condensate density vanishes, suggesting a phase transition to a non-Bose condensed nonequilibrium steady state.

Figure 5

The effective contact $C\left(k_n{a}_f\right)$ associated with the asymptotic momentum distribution function as a function of the interaction strength $k_n{a}_f$ to which the system is quenched from $k_n{a}_0=0.01$.