Abstract
Quantum fluctuations play a fundamental role in condensed matter
physics, determining the nature of the ground state of a many-body
system. For an ensemble of bosons at zero temperature, these
fluctuations deplete the condensate mode while populating higher
energy states [1]. The resulting many-body state exhibits strong
correlations, such as pairing between particles of opposite
momenta and characteristic tails in the momentum-space
distribution [2]. In this talk, I will present our recent
progress towards the observation of these signatures of quantum
depletion. Our experiments are performed with an ultracold gas of
metastable Helium-4 atoms for which electronic detection of
individual particles is possible [3], providing direct access to
the three-dimensional, momentum-space distribution of the gas. We
find characteristic power-law scaling of the depletion population
with momentum, in agreement with Bogoliubov's microscopic theory.
Importantly, our measurements are able to distinguish between
quantum and thermal effects, allowing for an unambiguous
identification of quantum depletion.
[1] N. N. Bogoliubov, J. Phys. (Moscow) 11, 23 (1947)
[2] L. Mathey et al, PRA 79, 013609 (2009)
[3] T. Jeltes et al., Nature 445, 402-405 (2007)