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SUMMARY:Does an isolated quantum system relax? - Joerg Schmiedmayer (VCQ\,
  Atominstitut\, TU-Wein)
DTSTART:20151102T153000Z
DTEND:20151102T170000Z
UID:TALK60777@talks.cam.ac.uk
CONTACT:6270
DESCRIPTION:Interfering two isolated one-dimensional quantum gases we stud
 y how the coherence created between the two many body systems by the split
 ting process slowly degrades by coupling to the many internal degrees of f
 reedom available [1]. Two distinct regimes are clearly visible: for short 
 length scales the system is characterized by spin diffusion\, for long len
 gth scales by spin decay [2]. For a sudden quench the system approaches a 
 pre-thermalized state [3]\, which is characterized by thermal like correla
 tion functions in the observed interference fringes with an effective temp
 erature over five times lower than the kinetic temperature of the initial 
 system.  A detailed study of the time evolution of the correlation functio
 ns reveals that these thermal-like properties emerge locally in their fina
 l form and propagate through the system in a light-cone-like evolution [4]
 . Furthermore we demonstrate\, that the pre-thermalized state is described
  by a generalized Gibbs ensemble [5]. This is verified through a detailed 
 study of the full non-translation invariant phase correlation functions up
  to 10th order. Finally we show two distinct ways for subsequent evolution
  away from the pre-thermalized state. One proceeds by further de-phasing\,
  the other by higher order phonon scattering processes.  In both cases the
  final state is indistinguishable from a thermally relaxed state.  We conj
 ecture that our experiments points to a universal way through which relaxa
 tion in isolated many body quantum systems proceeds if the low energy dyna
 mics is dominated by long lived excitations (quasi particles).\n\nSupporte
 d by the Wittgenstein Prize\, the Austrian Science Foundation (FWF) SFB Fo
 QuS: F40-P10 and the EU through the ERC-AdG QuantumRelax\n\n[1] S. Hofferb
 erth et al. Nature\, 449\, 324 (2007).\n[2]	M. Kuhnert et al.\, Phys. Rev.
  Lett\, 110\, 090405 (2013).\n[3] M. Gring et al.\, Science\, 337\, 1318 (
 2012)\; D. Adu Smith et al. NJP\, 15\, 075011 (2013).\n[4] T. Langen et al
 .\, Nature Physics\, 9\, 640–643 (2013).\n[5] T. Langen et al.\, Science
  348 207-211 (2015).\n\n\n
LOCATION:Rutherford building\, Seminar Room B
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