Coherent Perfect Absorption in a Parametric Cavity-Ensemble System

We propose a scheme to achieve CPA not only in the strong-coupling regime but also in the weak-coupling regime. The system under consideration consists of an atomic ensemble coupled to an optical cavity containing an optical parametric amplifier (OPA). We show that when the OPA introduces an effective loss, CPA can occur only in the strong-coupling regime. In contrast, when the OPA provides an effective gain, CPA can emerge in both the weak- and strong-coupling regimes. We further demonstrate that in the weak-coupling regime, CPA cannot occur within the bistable region, whereas in the strong-coupling regime, CPA can indeed appear in the bistable region. Moreover, the output intensity can be flexibly controlled by tuning the effective strength and the phase of the OPA. Our work opens a potential way to design a coherent perfect absorber based on weak coupling mechanism.