Quantum Coherence Regulated by Nanoparticles in a Whispering-Gallery-Mode Microresonator

A theoretical investigation of the macroscopic quantum coherence in a whispering-gallery-mode optical microresonator is conducted, where clockwise (CW) and counterclockwise (CCW) propagating modes are coupled in nonreciprocal non-Hermitian manner induced by nanoparticles. The results indicate that the dynamic control of quantum coherence/intercoherence can be realized by adjusting relative phase angle of the nanoparticles. A rather more exotic finding is that chiral optical quantum coherence can be achieved in the context of asymmetric backscattering. Especially in the vicinity of the exceptional point, chiral optical quantum coherence phenomenon is most obvious; that is, the CW(CCW) mode generated by backscattering exhibits strong quantum coherence while the coherence of CCW(CW) mode generated by backscattering is completely suppressed. Further, the optomechanical coherence between photons and phonons also shows chiral behavior. Finally, the experimental feasibility of quantum coherence is evaluated, and experimental scheme to readout and measure coherence is discussed briefly.