Enhanced nonlinear characteristics with the assistance of a $$\mathscr{PT}$$ 𝒫𝒯 -symmetric trimer system

Abstract We study the parity-time (PT) symmetry characteristics and the applications to nonlinear optics in an optical trimer system consisting of two indirectly coupled standing-mode micro-cavities and a two-level quantum emitter (QE) placed at the intersection of two cavities. We find this trimer system can exhibit analogical phenomena as those in typical $$\mathscr{PT}$$ 𝒫𝒯 -symmetric dimer systems composed of a passive cavity directly coupled to an active cavity. This system, whose $$\mathscr{PT}$$ 𝒫𝒯 symmetry is demonstrated by our analytic results, can be transformed between the $$\mathscr{PT}$$ 𝒫𝒯 -symmetric phase and the $$\mathscr{PT}$$ 𝒫𝒯 -broken phase by adjusting relevant system parameters. Then, with this system, we observe both the linear and nonlinear parts of the transmission field become remarkably enhanced and can further reach peak values around the $$\mathscr{PT}$$ 𝒫𝒯 breaking point. In addition, we show the negative correlation between the gain degree of the linear (nonlinear) transmission part and decay rate of the QE. This trimer proposal is feasible for experiments and may provide a promising platform for $$\mathscr{PT}$$ 𝒫𝒯 -symmetric optics of low-light levels. Moreover, novel phenomena arising from the QE-cavity-coupling induced nonlinearity gain could be explored to fabricate photonic devices and controllable nonlinear optical media for quantum information process and communication of photons.