Disorder-enhanced phase coherence in trapped bosons on optical lattices

TL;DR

This study uses quantum Monte Carlo simulations to reveal that disorder can enhance phase coherence in trapped bosons with a Mott plateau, due to a competition between localization and delocalization effects.

Contribution

It demonstrates that disorder can increase phase coherence in trapped bosons with a Mott plateau, a counterintuitive effect not previously well understood.

Findings

Disorder increases phase coherence in systems with a Mott plateau.

Localization and disorder effects compete, leading to partial delocalization.

Disordered states form a Bose glass phase in uniform systems.

Abstract

The consequences of disorder on interacting bosons trapped in optical lattices are investigated by quantum Monte Carlo simulations. At small to moderate strengths of potential disorder a unique effect is observed: if there is a Mott plateau at the center of the trap in the clean limit, phase coherence {\it increases} as a result of disorder. The localization effects due to correlation and disorder compete against each other, resulting in a partial delocalization of the particles in the Mott region, which in turn leads to increased phase coherence. In the absence of a Mott plateau, this effect is absent. A detailed analysis of the uniform system without a trap shows that the disordered states participate in a Bose glass phase.