  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.
