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

TL;DR

This paper demonstrates a non-equilibrium transition between delocalized and localized photon states in coupled circuit QED resonators, influenced by strong photon-qubit interactions and dissipation, with observable effects on qubit states.

Contribution

It reveals a sharp non-equilibrium delocalization-localization transition in circuit QED systems due to strong coupling and dissipation effects, and proposes an experimental observation method.

Findings

Dissipation favors photon self-trapping.

Transition can be observed without tuning system parameters.

Photon localization affects qubit states, enabling easy detection.

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.