Observation of thermal and quantum depletion in an interacting Bose gas (Orale)

David Clément

Isabelle Bouchoule

R. Chang, Quentin Bouton, Hugo Cayla +4 more

We report on the single-atom-resolved measurement of the distribution of momenta ℏk 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 off 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.

Thomas Bourdel

Laurent Sanchez-Palencia

Moulud Tamaddonpur, H. Yavari, Zahra Saeidi

The depletion of a quasi-two-dimensional (quasi-2D) dipolar Bose condensed gas in the presence of both contact and long-range 1/r interactions is investigated in the framework of Hartree–Fock–Bogoliubov (HFB) approximation. When the characteristic wavelength of a mode is much larger than the trap size, the dipole-dipole (DD) interaction can be treated as a contact interaction and in the low momentum limit the long-range nature of the 1/r interaction has the dominant contribution and leads to the nonlinear (nonphononic) dispersion relation. We will show that quantum depletion is temperature independent and is determined by the contact, DD and longrange 1/r coupling constants (ɛdd = gd/g and C). The the quantum depletion is affected by long-range 1/r interaction and at large momentum limits the momentum dependence of quantum depletion unaffected by 1/r interaction.