Non-equilibrium delocalization-localization transition of photons in circuit QED

Abstract: We show that photons in two tunnel-coupled microwave resonators each containing a single superconduct- ing qubit undergo a sharp non-equilibrium delocalization-localization (self-trapping) transition due to strong photon-qubit coupling. We find that dissipation favors the self-trapped regime and leads to the possibility of observing the transition as a function of time without tuning any parameter of the system. Furthermore, we find that self-trapping of photons in one of the resonators (spatial localization) forces the qubit in the opposite resonator to remain in its initial state (energetic localization). This allows for an easy experimental observation of the transition by local read-out of the qubit state.