Dissipative light-matter coupling and anomalous dispersion in nonideal cavities

We consider the scenario of an emitter embedded in a nonideal cavity. Using an input-output approach to describe the open system, we show that an effective dissipative coupling between the emitter and the cavity can emerge because of their interaction with a common photonic environment. The underlying mechanism is independent of the nature of the emitter and exists even at zero temperature; hence our results provide a pathway for accessing a range of non-Hermitian phenomena in a variety of light-matter coupled systems. In particular, we show that the effective dissipative coupling can lead to the phenomenon of level attraction between the emitter and cavity mode when the radiative decay rates exceed the conventional Rabi coupling. Our model thus provides a possible explanation for the anomalous dispersions and negative mass observed in recent photoluminescence measurements in semiconductor microcavities. Finally, we show that our effective non-Hermitian system can produce hybrid light-matter exceptional points and bound states in the continuum.