Expansion of a one-dimensional Bose gas: the role of interactions and kinetic-energy driving

TL;DR

This paper investigates how a one-dimensional Bose gas expands after a sudden increase in chain length, analyzing different initial states and expansion types, revealing non-equilibrium phenomena and the influence of interactions and kinetic driving.

Contribution

It provides exact numerical analysis of expansion dynamics for various initial states and expansion methods, highlighting the effects of interactions and kinetic driving on momentum correlations.

Findings

Reproduces non-equilibrium quasi-condensation into momenta ±π/2 from an insulator

Shows spectroscopic experiments reflect initial momentum distribution accurately

Analyzes momentum correlations and physical mechanisms during expansion

Abstract

We study the expansion of a one-dimensional boson gas by suddenly increasing the length of the chain where it resides. We consider three initial ground-state configurations: the Mott insulator, the conventional superfluid clumped around zero momentum, and the cat-like state with peaks at momenta $\pm \pi/2$, resulting from rapid kinetic driving. In turn, we consider three types of expansion: spectroscopic (with interactions tuned to zero), dynamic (with standard short-range repulsive interactions) and under kinetic driving. The numerical calculations are exact. We compute the momentum- and real-space one-particle densities as well as the two-particle momentum correlations. The spectroscopic time-of-flight experiment faithfully reflects the initial momentum distribution. For the dynamic expansion starting from an insulator, we reproduce the non-equilibrium quasi-condensation into momenta $\pm \pi/2$ while noticing correlations in the momentum distribution, and provide an intuitive physical picture. A discussion of various measures of the momentum correlations is also presented.