Quantum and semiclassical Non-Hermitian Dicke models without nonreciprocity

The Dicke model, which describes the collective interaction between an ensemble of atoms and a single-mode photon field, serves as a fundamental framework for studying light-matter interactions and quantum electrodynamic phenomena. In this work, we investigate the manifestation of nonHermitian effects in a generalized Dicke model, where two dissipative atom ensembles interact with a single-mode photon field. We explore the system in the semiclassical limit as a non-Hermitian Dicke model, revealing rich exceptional points (EPs) and diabolic points in such a system. Furthermore, we explore the quantum signature of EPs in the Hilbert space, relying on discrete photon numbers. The transition from photon antibunching to bunching at a steady state is unravelled. Our findings deepen the understanding of non-Hermitian physics in light-matter interaction, which is instructive for the design of advanced photonic devices.