Phase Coherence and Superfluid-Insulator Transition in a Disordered Bose-Einstein Condensate

TL;DR

This study investigates how disorder affects phase coherence and transport in a Bose-Einstein condensate, revealing a transition from coherent superfluid behavior to fragmented insulator states as disorder increases.

Contribution

It provides experimental insights into the superfluid-insulator transition in a disordered BEC, highlighting the role of phase coherence and density modulation.

Findings

Inhibited transport and damping at moderate disorder.

Reproducible interference patterns linked to density modulations.

Fragmentation with loss of phase coherence at high disorder.

Abstract

We have studied the effects of a disordered optical potential on the transport and phase coherence of a Bose-Einstein condensate (BEC) of 7Li atoms. At moderate disorder strengths (V_D), we observe inhibited transport and damping of dipole excitations, while in time-of-flight images, random but reproducible interference patterns are observed. In-situ images reveal that the appearance of interference is correlated with density modulation, without complete fragmentation. At higher V_D, the interference contrast diminishes as the BEC fragments into multiple pieces with little phase coherence.