Anisotropic 2D diffusive expansion of ultra-cold atoms in a disordered potential

TL;DR

This study investigates the anisotropic diffusion of ultra-cold atoms in a disordered potential, revealing energy-dependent diffusion coefficients and non-Gaussian density profiles through experimental and numerical analysis.

Contribution

It demonstrates the anisotropic and energy-dependent diffusion behavior of ultra-cold atoms in a disordered optical speckle potential with vertical confinement.

Findings

Diffusion is anisotropic due to the speckle orientation.

Density profiles are non-Gaussian during expansion.

Experimental diffusion coefficients agree with numerical models.

Abstract

We study the horizontal expansion of vertically confined ultra-cold atoms in the presence of disorder. Vertical confinement allows us to realize a situation with a few coupled harmonic oscillator quantum states. The disordered potential is created by an optical speckle at an angle of 30{\deg} with respect to the horizontal plane, resulting in an effective anisotropy of the correlation lengths of a factor of 2 in that plane. We observe diffusion leading to non-Gaussian density profiles. Diffusion coefficients, extracted from the experimental results, show anisotropy and strong energy dependence, in agreement with numerical calculations.