Short time dynamics after a wavefunction quench in 1D Bose gases*

Generalized hydrodynamics (GHD) has recently been shown to describe the dynamics in nearly-integrable 1D Bose gases very well, even after strong quenches of the trap [1]. We now study these gases shortly after a wavefunction quench, in which the atoms are put into a superposition of multiple momentum states by an axial Bragg pulse. After the quench, the gases are out of local equilibrium with the local generalized Gibbs ensemble (GGE), so GHD dose not apply. We measure how the momentum distribution of the center peak evolves up to the point that the local GGE is satisfied. We perform numerical calculations and GHD in the infinite coupling limit, to identify when the GGE is satisfied in that case [2,1]. We then apply this understanding to extracting the local equilibration time constants for different densities and coupling strengths. These time constants are at the frontier of what can be theoretically calculated about non-equilibrium nearly-integrable systems.

[1] N. Malvania, et al. Generalized hydrodynamics in strongly interacting 1D Bose gases. Science, 373.6559 (2021)

[2] R. Van den Berg, et al. Separation of time scales in a quantum Newton’s cradle. PRL, 116(22), 225302 (2016)