Phase coherence of an atomic Mott insulator

TL;DR

This paper studies the phase coherence in ultracold Bose gases in optical lattices, revealing persistent short-range coherence in the Mott insulator phase due to particle/hole pairs and identifying signatures of density redistribution.

Contribution

It demonstrates that phase coherence persists deep in the Mott insulator phase and links observed interference patterns to particle/hole admixtures and shell structure effects.

Findings

Short-range phase coherence persists in the Mott insulator.

Finite interference visibility due to particle/hole pairs.

Reproducible kinks indicate density redistribution.

Abstract

We investigate the phase coherence properties of ultracold Bose gases in optical lattices, with special emphasis on the Mott insulating phase. We show that phase coherence on short length scales persists even deep in the insulating phase, preserving a finite visibility of the interference pattern observed after free expansion. This behavior can be attributed to a coherent admixture of particle/hole pairs to the perfect Mott state for small but finite tunneling. In addition, small but reproducible ``kinks'' are seen in the visibility, in a broad range of atom numbers. We interpret them as signatures for density redistribution in the shell structure of the trapped Mott insulator.