Local atom-number fluctuations in quantum gases at finite temperature

TL;DR

This paper studies atom-number fluctuations in small regions of quantum gases at finite temperature, revealing deviations from thermodynamic predictions and highlighting effects of interactions and excitations.

Contribution

It provides a detailed analysis of local fluctuations in quantum gases, including new predictions for dipolar superfluids and comparison with experimental data.

Findings

Quenching of fluctuations in 2D superfluid Bose gases

Enhanced thermal fluctuations in dipolar superfluids near roton wavelength

Deviations from thermodynamic limit due to finite-size effects

Abstract

We investigate the number fluctuations in small cells of quantum gases pointing out important deviations from the thermodynamic limit fixed by the isothermal compressibility. Both quantum and thermal fluctuations in weakly as well as highly compressible fluids are considered. For the two-dimensional (2D) superfluid Bose gas we find a significant quenching of fluctuations with respect to the thermodynamic limit, in agreement with recent experimental findings. An enhancement of the thermal fluctuations is instead predicted for the 2D dipolar superfluid Bose gas, which becomes dramatic when the size of the sample cell is of the order of the wavelength of the rotonic excitation induced by the interaction.