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SUMMARY:Many-body localization: a macroscopic quantum phenomena in highly 
 excited states - Arijeet Pal\, Princeton University
DTSTART:20140618T143000Z
DTEND:20140618T153000Z
UID:TALK53056@talks.cam.ac.uk
CONTACT:Dr G Moller
DESCRIPTION:In 1958 P. W. Anderson showed that eigenstates of a\nsingle-pa
 rticle quantum Hamiltonian in the presence of disorder can be\nlocalized i
 n space. In the same paper he had speculated on the possibility\nof lack o
 f thermalization in an isolated quantum system even in the\npresence of in
 teractions. There is now growing evidence that such an\nisolated system in
  the presence of strong disorder fails to\n\\it{equilibrate}. This phenome
 na is being referred to as \\it{many-body\nlocalization} (MBL).\n      I w
 ill introduce the various defining characteristics of the MBL\nphase and t
 he measures which can be used to distinguish it from\nthe ergodic phase. B
 ased on these I will show numerical evidence\nof the hypothesized phase-tr
 ansition between the MBL and thermal\nphases in a short-ranged model. I wi
 ll also describe the many-body\nlocalization-delocalization (MBLD) transit
 ion in the quantum\nrandom energy model. It is the "simplest" mean-field m
 odel for the\nequilibrium spin-glass transition. Its analytical tractabili
 ty\nopens the possibility to develop a mean-field understanding of the\ndy
 namical critical point. Due to the violation of ergodicity MBL\neven allow
 s the existence of symmetry-breaking and topological\norder even in highly
  excited eigenstates\, which would normally be\ndestroyed by thermal fluct
 uations at equilibrium. I will present a\nphenomenological description of 
 this localization protected\nquantum order.
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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