Phase transitions, such as the change of liquid water into ice, help elucidate the complex behavior of systems composed of many particles and occur in all areas of physics. Recently, theorists have predicted that a cavity containing only a single atom should transition from opaque to transparent when the input photon flux reaches a critical number. And just as water and ice can coexist at the melting point temperature, the cavity was predicted to be both opaque and transparent close to the critical point, stochastically switching between the two states. This coexistence is a hallmark for a so-called first-order phase transition, which has been observed for the first time in a dissipative quantum system.

The article in Physical Review X and the IST press release as well as some news coverage on  DerStandard.