Momentum-resolved observation of thermal and quantum depletion in an interacting Bose gas

TL;DR

This study uses single-atom-resolved measurements to distinguish thermal and quantum depletion in an interacting Bose gas, revealing their momentum dependencies and confirming theoretical predictions about quantum depletion.

Contribution

It provides the first momentum-resolved experimental observation of quantum depletion in a Bose gas, confirming Bogoliubov theory predictions.

Findings

Thermal depletion identified by its temperature dependence.

Quantum depletion characterized by a $k^{-4}$ tail in momentum distribution.

Quantum depletion magnitude increases with condensate density.

Abstract

We report on the single-atom-resolved measurement of the distribution of momenta $\hbar k$ in a weakly interacting Bose gas after a 330 ms time-of-flight. We investigate it for various temperatures and clearly separate two contributions to the depletion of the condensate by their $k$-dependence. The first one is the thermal depletion. The second contribution falls of as $k^{-4}$, and its magnitude increases with the in-trap condensate density as predicted by the Bogoliubov theory at zero temperature. These observations suggest associating it with the quantum depletion. How this contribution can survive the expansion of the released interacting condensate is an intriguing open question.