Canonical ensemble of an interacting Bose gas: stochastic matter fields and their coherence

TL;DR

This paper introduces a new stochastic matter field equation for weakly interacting Bose gases, accurately capturing both condensed and thermal atoms, and enabling detailed analysis of spatial coherence and fluctuations in ultracold gases.

Contribution

The authors develop a novel quantum stochastic evolution equation that is exact in the ideal limit and stable numerically, unifying the description of condensed and thermal atoms in ultracold Bose gases.

Findings

Accurate description of ground state occupation and fluctuations

Analysis of density profiles of ground state and thermal cloud

Investigation of spatial coherence via interference contrast

Abstract

We present a novel quantum stochastic evolution equation for a matter field describing the canonical state of a weakly interacting ultracold Bose gas. In the ideal gas limit our approach is exact. This numerically very stable equation suppresses high-energy fluctuations exponentially, which enables us to describe condensed and thermal atoms within the same formalism. We present applications to ground state occupation and fluctuations, density profile of ground state and thermal cloud, and ground state number statistics. Our main aim are spatial coherence properties which we investigate through the determination of interference contrast and spatial density correlations. Parameters are taken from actual experiments [1]. [1] S. Hofferberth et al., Nature Physics 4, 489 (2008).