Hanbury-Brown and Twiss bunching of phonons and of the quantum depletion in a strongly-interacting Bose gas

TL;DR

This study demonstrates that Hanbury-Brown and Twiss experiments with strongly interacting Bose gases reveal unique quantum correlations, providing insights into the quantum depletion and collective excitations beyond non-interacting particle behavior.

Contribution

It presents the first HBT-like measurement of correlations in a strongly interacting Bose gas, highlighting deviations from non-interacting predictions and probing quantum depletion and phonons.

Findings

Observed HBT bunching in the non-condensed fraction

Correlations reflect quantum depletion and Bogoliubov phonons

Deviations from non-interacting boson HBT signals

Abstract

We report the realisation of a Hanbury-Brown and Twiss (HBT)-like experiment with a gas of strongly interacting bosons at low temperatures. The regime of large interactions and low temperatures is reached in a three-dimensional optical lattice and atom-atom correlations are extracted from the detection of individual metastable Helium atoms after a long free-fall. We observe a HBT bunching in the non-condensed fraction of the gas whose properties strongly deviate from the HBT signals expected for non-interacting bosons. In addition, we show that the measured correlations reflect the peculiar quantum statistics of atoms belonging to the quantum depletion and of the Bogoliubov phonons, i.e., of collective excitations of the many-body quantum state. Our results demonstrate that atom-atom correlations provide information about the quantum state of strongly-interacting particles, extending the interest of HBT-like experiments beyond the case of non-interacting particles.