The interplay of quantum fluctuations with interactions lies at the core of quantum many-body physics, and generates specific particle correlations that could be revealed in experiments. A conceptually simple and emblematic example is the quantum depletion, present in the ground state of an ensemble of weakly-interacting bosons. It is composed of virtual pairs of bosons at opposite momenta, continuously coming in and out of the condensate, and should manifest in momentum-space correlations. I will report our recent observation of pairs of atoms with opposite momenta in an interacting Bose gas at equilibrium .
This experiment exploits the single-atom detection of metastable Helium in the momentum space  and the adiabatic preparation of interacting lattice gases . We have studied the properties of the pair correlations (i.e. amplitude and width) and contrast them with those of Hanbury-Brown and Twiss type of correlations , to highlight the quantum coherences of the virtual pairs in the many-body ground state. I will discuss these observations in the textbook description of the Bogoliubov theory .
 A. Tenart et al., in preparation (2021).
 H. Cayla et al., Phys. Rev. A 97, 061609(R) (2018).
 C. Carcy et al., Phys. Rev. Lett. 126, 045301 (2021).
 H. Cayla et al., Phys. Rev. Lett. 125, 165301 (2020).
 S. Butera et al., Phys. Rev. A 103, 013302 (2021).
Meeting ID: 861 7391 2183