Hydrodynamics of the interacting Bose gas in the Quantum Newton Cradle setup

TL;DR

This paper uses generalized hydrodynamics to numerically analyze the out-of-equilibrium dynamics of an interacting one-dimensional Bose gas in a setup similar to the Quantum Newton Cradle experiment, revealing detailed phase-space evolution and effects of anharmonicity.

Contribution

It provides the first comprehensive numerical study of the full phase-space dynamics of an interacting Bose gas in this experimental setup using generalized hydrodynamics.

Findings

Observed small elongation of oscillation period due to many-body effects

Identified cloud deformations caused by many-body dephasing

Characterized the time to reach the asymptotic quasi-particle distribution

Abstract

Describing and understanding the motion of quantum gases out of equilibrium is one of the most important modern challenges for theorists. In the groundbreaking Quantum Newton Cradle experiment [Kinoshita, Wenger and Weiss, Nature 440, 900, 2006], quasi-one-dimensional cold atom gases were observed with unprecedented accuracy, providing impetus for many developments on the effects of low dimensionality in out-of-equilibrium physics. But it is only recently that the theory of generalized hydrodynamics has provided the adequate tools for a numerically efficient description. Using it, we give a complete numerical study of the time evolution of an ultracold atomic gas in this setup, in an interacting parameter regime close to that of the original experiment. We evaluate the full evolving phase-space distribution of particles. We simulate oscillations due to the harmonic trap, the collision of clouds without thermalization, and observe a small elongation of the actual oscillation period and cloud deformations due to many-body dephasing. We also analyze the effects of weak anharmonicity. In the experiment, measurements are made after release from the one-dimensional trap. We evaluate the gas density curves after such a release, characterizing the actual time necessary for reaching the asymptotic state where the integrable quasi-particle momentum distribution function emerges.