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SUMMARY:Single-atom and momentum-resolved measurement of the depletion of 
 a Bose condensate - David Clement (Institut Optique\, France)
DTSTART:20161024T143000Z
DTEND:20161024T160000Z
UID:TALK68365@talks.cam.ac.uk
CONTACT:6270
DESCRIPTION:The interplay of quantum fluctuations and interaction is at th
 e core of intriguing phenomena of\nquantum many-body physics. An emblemati
 c example\, conceptually rather simple\, of such a\nmanifestation is the q
 uantum depletion of a Bose condensate occurring at zero temperature. The\n
 resulting many-body ground-state\, a vacuum of quasi-particles\, is compos
 ed of single-particle\nexcitations on top of the condensate\, for which a 
 direct observation has been missing. I will report\non the single-atom-res
 olved measurement of the distribution of momenta hk in a weakly-interactin
 g\nBose gas after a 330 ms time-of-flight [1]. We investigate it for vario
 us temperatures and clearly\nseparated and identify\, by their k-dependenc
 e\, two distinct contributions to the depletion of the\ncondensate. One co
 ntribution can be unambiguously associated with the thermal depletion. Tha
 nks\nto a total dynamic range spanning five decades in density\, we observ
 e a second contribution\nconsisting in high-momentum tails decaying as 1/k
 ^4\, as predicted by Bogoliubov theory for the intrap\nBose gas [2]. We al
 so find that the population in the 1/k^4-tails increases with the in-trap\
 ncondensate density as expected for the quantum depletion but the amplitud
 e we measure is larger\nthan the Bogoliubov prediction by a factor of abou
 t 6. Our observations suggest to associate the 1/\nk^4-tails to the quantu
 m depletion of the trapped condensate and raise new theoretical questions 
 [3].\n[1] R. Chang\, Q. Bouton\, H. Cayla\, C. Qu\, A. Aspect\, C. Westbro
 ok and D. Clément\, arXiv:\n1608.04693 (2016).\n[2] N. N. Bogoliubov\, J.
  Phys. (Moscow) 11\, 23 (1947).\n[3] C. Qu\, L. Pitaevskii and S. Stringar
 i\, arXiv:1608.08566 (2016).
LOCATION:Ryle Seminar Room (930) 
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