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CATEGORIES:AMOP list
SUMMARY:Anomalous momentum diffusion of strongly interacti
ng bosons in optical lattices - Dr. Fabrice Gerbie
r\, Ecole Normale Supeerieure Paris\, France
DTSTART;TZID=Europe/London:20180611T153000
DTEND;TZID=Europe/London:20180611T163000
UID:TALK106897AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/106897
DESCRIPTION:Dissipative quantum systems are subject to decoher
ence\, the disappearance of interference phenomena
due to irreversible loss of information. This pla
ys a role in many modern areas of research\, from
research on the foundations of quantum mechanics t
o quantum information processing (and quantum tech
nologies in general)\, where decoherence is a thre
at that must be countered. While decoherence has b
een extensively studied for simple systems\, such
as a two-level atom or a harmonic oscillator\, muc
h less is known for many-body systems of interacti
ng particles. In this talk\, I will report on an e
xperimental study of how spatial coherence in a su
perfluid gas of bosonic atoms in an optical lattic
e is lost when the atoms undergo spontaneous emiss
ion. For independent atoms excited by a near-reson
ant laser\, repeated laser photon absorption-spont
aneous emission cycles destroy spatial coherences
on distances larger than the wavelength of the opt
ical transition\, or equivalently leads to diffusi
on in momentum space with a momentum width scaling
as t^(1/2). This momentum diffusion process is we
ll-known in quantum optics and limits the temperat
ure achievable in laser cooling. For strongly inte
racting bosons\, we observed that the momentum dif
fusion is anomalously slow: After a short time\, t
he decay of spatial coherences slows down\, and mo
mentum space dynamics becomes sub-diffusive with a
momentum width scaling as t^(1/4). We explain thi
s behavior in terms of a model proposed by Poletti
et al. [1]\, where the long-times dynamics is und
erstood in terms of a diffusion in Fock space. Dis
sipation leads to the formation of "long-lived" cl
usters of atoms with higher occupancy than the ave
rage site. These clusters decay slowly (through hi
gh-order processes) due to their energy mismatch w
ith more typical configurations. In classical stat
istical mechanics\, the transport dynamics of syst
ems with a distribution of lifetimes featuring a s
low tail typically shows sub-diffusion [2]. Using
three-body losses as a probe of on site statistics
\, we provide a direct evidence of this anomalous
diffusion in Fock space which underlies the anomal
ous momentum diffusion.\n\n[1] D. Poletti et al.\,
Phys. Rev. Lett. 109\, 045302 (2012)\; D. Poletti
et al.\, Phys. Rev. Lett. 111\, 195301 (2013).\n[
2] J.-P. Bouchaud\, A. Georges\, Physics reports 1
95 (4-5)\, 127-29 (1990).
LOCATION:Ryle Seminar Room (930)
CONTACT:Dr Ulrich Schneider
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