Epidemic spreading and herd immunity in a driven non-equilibrium system of strongly-interacting atoms.

It is increasingly important to understand the spatial dynamics of epidemics. While there are numerous mathematical models of epidemics, there is a scarcity of physical systems with sufficiently well-controlled parameters to allow quantitative model testing. It is also challenging to replicate the macro non-equilibrium effects of complex models in microscopic systems. In this work, we demonstrate experimentally a physics analog of epidemic spreading using optically-driven non-equilibrium phase transitions in strongly interacting Rydberg atoms. Using multiple laser beams we can impose any desired spatial structure. The observed spatially localized phase transitions simulate the outbreak of an infectious disease in multiple locations, and the splitting of the outbreak in subregions, as well as the dynamics towards "herd immunity" and "endemic state" in different regimes. The reported results indicate that Rydberg systems are versatile enough to model complex spatial-temporal dynamics. [ABSTRACT FROM AUTHOR]