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Recent developments in diverse areas - ranging from cold atomic gases over light driven semiconductors to microcavity arrays - move systems into the focus, which are located on the interface of quantum optics, many-body physics and statistical mechanics. These "driven open quantum systems" share in common that coherent and driven-dissipative dynamics occur on an equal footing, creating genuine non-equilibrium scenarios without immediate counterpart in equilibrium condensed matter physics. A case in point are so-called exciton-polaritons in two spatial dimensions. We briefly explain the physical basis, their description, and how to detect the violation of thermal equilibrium conditions in the formalism. We then show that a paradigmatic hallmark of low-temperature equilibrium systems -- the presence of quasi-long range order, i.e. the algebraic decay of spatial correlation functions -- must be absent due to non-equilibrium conditions. This conclusion is drawn based on a connection to the problem of surface roughening.

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Sebastian Diehl, ITP
TP seminar room 0.03
Contact: Joachim Krug