Expansion dynamics of interacting bosons in homogeneous lattices in one and two dimensions

TL;DR

This study explores how the expansion of ultracold bosons in optical lattices varies with dimensionality and interaction strength, revealing ballistic, diffusive, and crossover behaviors in non-equilibrium dynamics.

Contribution

It provides experimental and numerical insights into the dimensional crossover and interaction effects on bosonic expansion in optical lattices.

Findings

Ballistic expansion in integrable limits

Suppressed expansion with bimodal cloud shapes

Dimensional crossover from ballistic to diffusive dynamics

Abstract

We experimentally and numerically investigate the expansion of initially localized ultracold bosons in homogeneous one- and two-dimensional optical lattices. We find that both dimensionality and interaction strength crucially influence these non-equilibrium dynamics. While the atoms expand ballistically in all integrable limits, deviations from these limits dramatically suppress the expansion and lead to the appearance of almost bimodal cloud shapes, indicating diffusive dynamics in the center surrounded by ballistic wings. For strongly interacting bosons, we observe a dimensional crossover of the dynamics from ballistic in the one-dimensional hard-core case to diffusive in two dimensions, as well as a similar crossover when higher occupancies are introduced into the system.