Probing three-body correlations in a quantum gas using the measurement of the third moment of density fluctuations

TL;DR

This study measures the third moment of density fluctuations in a quantum Bose gas, revealing three-body correlations and testing thermodynamic models, with results aligning with modified Yang-Yang predictions.

Contribution

It introduces a method to measure the third moment of atom number fluctuations, providing direct evidence of three-body correlations in a quantum gas.

Findings

Positive skewness in ideal gas regime

Reduced skewness in quasi-condensate regime

Agreement with modified Yang-Yang thermodynamics

Abstract

We perform measurements of the third moment of atom number fluctuations in small slices of a very elongated weakly interacting degenerate Bose gas. We find a positive skewness of the atom number distribution in the ideal gas regime and a reduced skewness compatible with zero in the quasi-condensate regime. For our parameters, the third moment is a thermodynamic quantity whose measurement constitutes a sensitive test of the equation of state and our results are in agreement with a modified Yang-Yang thermodynamic prediction. Moreover, we show that the measured skewness reveals the presence of true three body correlations in the system.