Recurrent delocalization and quasi-equilibration of photons in coupled circuit QED systems

TL;DR

This paper investigates photon dynamics in coupled circuit QED systems, revealing phase transitions between delocalized and localized states, and identifying a novel quasi-equilibrated delocalized phase due to nonlinear effects in the ultrastrong coupling regime.

Contribution

It uncovers a new phase of photon behavior involving quasi-equilibration and highlights the importance of nonlinear effects in ultrastrong coupling regimes.

Findings

Photon population transitions from delocalized to localized and back to delocalized phases.

Identification of a quasi-equilibrated delocalized phase with rapid photon distribution.

Nonlinear behaviors significantly influence photon dynamics in ultrastrong coupling.

Abstract

We explore the photon population dynamics in two coupled circuit QED systems. For a sufficiently weak inter-cavity photon hopping, as the photon-cavity coupling increases, the dynamics undergoes double transitions first from a delocalized to a localized phase and then from the localized to another delocalized phase. The latter delocalized phase is distinguished from the former one; instead of oscillating between the two cavities, the photons rapidly quasi-equilibrate over the two cavities. These intrigues are attributed to an interplay between two qualitatively distinctive nonlinear behaviors of the circuit QED systems in the utrastrong coupling regime, whose distinction has been widely overlooked.