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SUMMARY:Anomalous momentum diffusion of strongly interacting bosons in opt
 ical lattices - Dr. Fabrice Gerbier\, Ecole Normale Supeerieure Paris\, Fr
 ance
DTSTART:20180611T143000Z
DTEND:20180611T153000Z
UID:TALK106897@talks.cam.ac.uk
CONTACT:Dr Ulrich Schneider
DESCRIPTION:Dissipative quantum systems are subject to decoherence\, the d
 isappearance of interference phenomena due to irreversible loss of informa
 tion. This plays a role in many modern areas of research\, from research o
 n the foundations of quantum mechanics to quantum information processing (
 and quantum technologies in general)\, where decoherence is a threat that 
 must be countered. While decoherence has been extensively studied for simp
 le systems\, such as a two-level atom or a harmonic oscillator\, much less
  is known for many-body systems of interacting particles. In this talk\, I
  will report on an experimental study of how spatial coherence in a superf
 luid gas of bosonic atoms in an optical lattice is lost when the atoms und
 ergo spontaneous emission. For independent atoms excited by a near-resonan
 t laser\, repeated laser photon absorption-spontaneous emission cycles des
 troy spatial coherences on distances larger than the wavelength of the opt
 ical transition\, or equivalently leads to diffusion in momentum space wit
 h a momentum width scaling as t^(1/2). This momentum diffusion process is 
 well-known in quantum optics and limits the temperature achievable in lase
 r cooling. For strongly interacting bosons\, we observed that the momentum
  diffusion is anomalously slow: After a short time\, the decay of spatial 
 coherences slows down\, and momentum space dynamics becomes sub-diffusive 
 with a momentum width scaling as t^(1/4). We explain this behavior in term
 s of a model proposed by Poletti et al. [1]\, where the long-times dynamic
 s is understood in terms of a diffusion in Fock space. Dissipation leads t
 o the formation of "long-lived" clusters of atoms with higher occupancy th
 an the average site. These clusters decay slowly (through high-order proce
 sses) due to their energy mismatch with more typical configurations. In cl
 assical statistical mechanics\, the transport dynamics of systems with a d
 istribution of lifetimes featuring a slow tail typically shows sub-diffusi
 on [2]. Using three-body losses as a probe of on site statistics\, we prov
 ide a direct evidence of this anomalous diffusion in Fock space which unde
 rlies the anomalous momentum diffusion.\n\n[1] D. Poletti et al.\, Phys. R
 ev. Lett. 109\, 045302 (2012)\; D. Poletti et al.\, Phys. Rev. Lett. 111\,
  195301 (2013).\n[2] J.-P. Bouchaud\, A. Georges\, Physics reports 195 (4-
 5)\, 127-29 (1990).
LOCATION:Ryle Seminar Room (930) 
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