Recurrent Delocalization and Quasiequilibration of Photons in Coupled Systems in Circuit Quantum Electrodynamics

Charged particles can interact with each other, or feel the presence of other charged particles, through the Coulomb interaction. While such an interaction mechanism does not naturally exist for photons, it is well-known that a single atom placed inside of a cavity can mediate an interaction among photons inside of the cavity. The magnitude of this induced photon-photon interaction is often thought to monotonically increase as a function of the atom-photon interaction strength. Contrary to this belief, we show in our work that beyond a certain threshold value, the stronger atom-photon interaction starts to reduce the induced photon-photon interaction. This rather counter-intuitive property of the induced photon-photon interaction is discussed in the context of the photon population dynamics in a coupled cavity array where there occurs a double dynamical transition from a delocalization to localization, back to delocalization, of the photon population. Moreover, it is found that the second delocalization dynamics shows a quasi-equilibration despite of being a closed, finite quantum system.

Recurrent Delocalization and Quasiequilibration of Photons in Coupled Systems in Circuit Quantum Electrodynamics