Momentum distribution of 1D Bose gases at the quasi-condensation crossover: theoretical and experimental investigation

TL;DR

This study combines experimental measurements and theoretical calculations to analyze the momentum distribution of 1D Bose gases at the quasi-condensation crossover, providing improved thermometry and insights into the applicability of classical field theory.

Contribution

It presents an improved focusing technique for measuring momentum distribution and compares experimental results with quantum Monte Carlo simulations to assess classical field theory validity.

Findings

Momentum distribution matches quantum Monte Carlo calculations.

Classical field theory is often invalid due to strong interactions.

Enhanced thermometry method based on momentum distribution.

Abstract

We investigate the momentum distribution of weakly interacting 1D Bose gases at thermal equilibrium both experimentally and theoretically. Momentum distribution of single 1D Bose gases is measured using a focusing technique, whose resolution we improve via a guiding scheme. The momentum distribution compares very well with quantum Monte Carlo calculations for the Lieb-Liniger model at finite temperature, allowing for an accurate thermometry of the gas that agrees with (and improves upon) the thermometry based on in situ density fluctuation measurements. The quasi-condensation crossover is investigated via two different experimental parameter sets, corresponding to the two different sides of the crossover. Classical field theory is expected to correctly describe the quasi-condensation crossover of weakly interacting gases. We derive the condition of validity of the classical field theory, and find that, in typical experiments, interactions are too strong for this theory to be accurate. This is confirmed by a comparison between the classical field predictions and the numerically exact quantum Monte Carlo calculations.