title: Absorbing State Phase Transition with Competing Quantum and Classical Fluctuations.
abstract: Stochastic processes with absorbing states feature examples of nonequilibrium universal phenomena. While the classical regime has been thoroughly investigated in the past, relatively little is known about the behavior of these nonequilibrium systems in the presence of quantum fluctuations. Here, we theoretically address such a scenario in an open quantum spin model which, in its classical limit, undergoes a directed percolation phase transition. By mapping the problem to a nonequilibrium field theory, we show that the introduction of quantum fluctuations stemming from coherent, rather than statistical, spin flips alters the nature of the transition such that it becomes first order. In the intermediate regime, where classical and quantum dynamics compete on equal terms, we highlight the presence of a bicritical point with universal features different from the directed percolation class in a low dimension. We finally propose how this physics could be explored within gases of interacting atoms excited to Rydberg states.
authors.affiliation: School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
authors.forename: Matteo
authors.initials: M
authors.lastname: Marcuzzi
authors.affiliation: Institut für Theoretische Physik, Universität zu Köln, D-50937 Cologne, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Buchhold
authors.affiliation: Institut für Theoretische Physik, Universität zu Köln, D-50937 Cologne, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Diehl
authors.affiliation: School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom.
authors.forename: Igor
authors.initials: I
authors.lastname: Lesanovsky