Momentum-space correlations of a one-dimensional Bose gas

TL;DR

This study measures and analyzes momentum-space density correlations in a one-dimensional Bose gas across different interaction regimes, revealing the presence of bunching and negative correlations not predicted by traditional theories.

Contribution

First experimental measurement of full momentum-space density correlations in a 1D Bose gas across various regimes, including the quasicondensate phase.

Findings

Bunching observed in all regimes.

Negative correlations between different momenta in the quasicondensate regime.

Experimental data agrees with ab-initio calculations.

Abstract

Analyzing the noise in the momentum profiles of single realizations of one-dimensional Bose gases, we present the experimental measurement of the full momentum-space density correlations $\langle \delta n_p \delta n_{p'}\rangle$, which are related to the two-body momentum correlation function. Our data span the weakly interacting region of the phase diagram, going from the the ideal Bose gas regime to the quasicondensate regime. We show experimentally that the bunching phenomenon, which manifests itself as super-Poissonian local fluctuations in momentum space, is present in all regimes. The quasicondensate regime is however characterized by the presence of negative correlations between different momenta, in contrast to Bogolyubov theory for Bose condensates, predicting positive correlations between opposite momenta. Our data are in good agreement with {\it ab-initio} calculations.