Quantum Joule-Thomson Effect in a Saturated Homogeneous Bose Gas

TL;DR

This paper demonstrates the quantum Joule-Thomson effect in a saturated homogeneous Bose gas, showing significant cooling due to energy-independent collisions and highlighting quantum statistical effects on thermodynamics.

Contribution

First experimental observation of the quantum Joule-Thomson effect in a weakly interacting Bose gas within an optical-box trap.

Findings

Observed saturation of the thermal component at the critical point.

Measured Joule-Thomson coefficient exceeding classical values by ten orders of magnitude.

Demonstrated spontaneous isoenthalpic cooling due to background gas collisions.

Abstract

We study the thermodynamics of Bose-Einstein condensation in a weakly interacting quasi-homogeneous atomic gas, prepared in an optical-box trap. We characterise the critical point for condensation and observe saturation of the thermal component in a partially condensed cloud, in agreement with Einstein's textbook picture of a purely statistical phase transition. Finally, we observe the quantum Joule-Thomson effect, namely isoenthalpic cooling of an (essentially) ideal gas. In our experiments this cooling occurs spontaneously, due to energy-independent collisions with the background gas in the vacuum chamber. We extract a Joule-Thomson coefficient $\mu_{\rm JT} > 10^9$ K/bar, about ten orders of magnitude larger than observed in classical gases.