Observations of density fluctuations in an elongated Bose gas: ideal gas and quasi-condensate regimes

TL;DR

This study measures density fluctuations in a quasi-1D Bose gas, revealing ideal gas behavior at low densities and interaction-induced suppression at high densities, enhancing understanding of quantum many-body effects.

Contribution

First in situ measurements of density fluctuations in a quasi-1D Bose gas across different regimes, comparing ideal and interacting cases.

Findings

Fluctuations match ideal Bose gas bunching at low density.

Fluctuations are suppressed at high density due to interactions.

Data agree with theoretical models for quasi-condensate regime.

Abstract

We report in situ measurements of density fluctuations in a quasi one dimensional Bose gas at thermal equilibrium in an elongated harmonic trap. We observe an excess of fluctuations compared to the shot noise level expected for uncorrelated atoms. At low atomic density, the measured excess is in good agreement with the expected bunching for an ideal Bose gas. At high density, the measured fluctuations are strongly reduced compared to the ideal gas case. We attribute this reduction to repulsive interatomic interactions. The data are compared with a calculation for an interacting Bose gas in the quasi-condensate regime.