Non-equilibrium steady states of quantum critical systems Seminar

If two independent systems, initially thermalized at different temperatures, are joined together on some hypersurface, then energy should start flowing from the hotter to the cooler. If the systems are of infinite extent, then one may expect that after a very large time, a (non-equilibrium) steady state with constant energy flow will be reached. We have universal predictions for the existence of this steady state and for the energy current and fluctuations that it carries, whenever the two systems are two halves of an infinite-volume d-dimensional quantum critical system. At d=1, these are exact results from the powerful techniques of d=1 CFT, which can in fact be generalized to massive integrable models. At d>1, these follow from considerations of gauge-gravity duality, conformal hydrodynamics, and quantum field theory. I will describe these predictions and the underlying methods. This is based on works in various collaborations: with Denis Bernard, with Joe Bhaseen, Andy Lucas and Koenraad Schalm, and with Olalla Castro-Alvaredo, Yixiong Chen and Marianne Hoogeveen.