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SUMMARY:Non-equilibrium steady states in many-body quantum systems - Benja
 min Doyon\, King's College London
DTSTART:20150312T141500Z
DTEND:20150312T154500Z
UID:TALK58181@talks.cam.ac.uk
CONTACT:Dr G Moller
DESCRIPTION:Let an infinite\, homogeneous\, many-body quantum system be un
 itarily evolved for a long time from a state where two halves are independ
 ently thermalized. If there are nonzero steady currents in the central reg
 ion then we say that a non-equilibrium steady state emerges\; their presen
 ce is a signature of ballistic transport. I will discuss some recent resul
 ts for such non-equilibrium steady states in any dimensionality\, obtained
  with my collaborators Denis Bernard and Marianne Hoogeveen\, and Joe Bhas
 een\, Andrew Lucas and Koenraad Schalm. I will first discuss a simple and 
 general bound on the average current and on the noise\, which occur\, unde
 r certain conditions\, from the Lieb-Robinson bound. This suggests to defi
 ne a natural velocity parameter bounded by the Lieb-Robinson velocity:  it
  is a ``nonlinear sound velocities''\, specializing to the sound velocity 
 near equilibrium in non-integrable models and to a ``generalized sound vel
 ocities'' encoding generalized Gibbs thermalization in integrable models. 
 Then\, I will discuss explicit results concentrating on conformal field th
 eories. I will explain how to obtain the exact current in one dimension us
 ing chiral factorization\, and how this generalizes in two separate ways t
 o higher dimensions: for interacting models using fluid dynamics and AdS/C
 FT ideas\, and for non-interacting models where independent mode thermaliz
 ation occurs. Interestingly\, the general bound is saturated at one-dimens
 ional criticality\, and in interacting models\, the nonlinear sound veloci
 ty has an explicit physical realization as the velocity of (almost-)shock 
 waves emanating form the contact hypersurface. If time permits\, I will ex
 plain how ``extended fluctuation relations'' hold in all cases\, leading a
 n exact description of the large-time fluctuations (interpreted as indepen
 dent Poisson processes).\n
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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