Collective radiance effects in the ultrastrong-coupling regime

Abstract

We investigate the collective radiance characteristics of qubits in the ultrastrong-coupling regime, where the radiance witness is defined based on the resonator-qubit dressed basis. An ultrastrong hyperradiance effect is demonstrated when the dressed state of the system is resonantly driven. Interestingly, we show that, besides the resonator-qubit coupling strength, the parity-symmetry-breaking-induced cascade transition can significantly enhance the collective radiance of the qubits, which allows us to manipulate the transitions between subradiance, superradiance, and hyperradiance via adjusting the parity symmetry of the system with an external magnetic field. This work extends the collective radiance theory to the ultrastrong-coupling regime, and offers potential applications in the engineering of laser devices.