Title: Epidemic dynamics in open quantum spin systems,
Abstract: We explore the non-equilibrium evolution and stationary states of an open
many-body system which displays epidemic spreading dynamics in a classical and
a quantum regime. Our study is motivated by recent experiments conducted in
strongly interacting gases of highly excited Rydberg atoms where the
facilitated excitation of Rydberg states competes with radiative decay. These
systems approximately implement open quantum versions of models for population
dynamics or disease spreading where species can be in a healthy, infected or
immune state. We show that in a two-dimensional lattice, depending on the
dominance of either classical or quantum effects, the system may display a
different kind of non-equilibrium phase transition. We moreover discuss the
observability of our findings in laser driven Rydberg gases with particular
focus on the role of long-range interactions.