Spontaneous PT-symmetry breaking in lasing dynamics

Parity-time (PT) symmetric lasers exploit the modulation of optical gain and loss and have led to important fundamental demonstrations in non-Hermitian physics. The current theoretical analysis of PT-symmetric laser physics is performed on the basis of the adiabatic elimination of the medium polarization. This approximation doesn't hold true for a more general optical system with strong photon-particle interactions, where the Rabi oscillation of active particles plays a non-negligible role in the lasing action. Here, we propose a model that takes into account the internal dynamics of active particles and numerically investigate the PT symmetry of macroscopic- and microscopic-sized laser systems that operate in the strong-coupling regime. The distinct phase diagrams are drawn according to the features of intracavity photon numbers and emission spectra. Our work extends the PT-symmetric optics from the weak- to the strong19 coupling limit, potentially paving the way towards nonclassical PT-symmetric light sources for integrated photonic networks and ultrasensitive sensors.