Thermal-Noise Cancellation for Optomechanically Induced Nonreciprocity in a Whispering-Gallery-Mode Microresonator

Magnetic-free optomechanically induced nonreciprocity may stimulate a wide range of practical applications in quantum technologies. However, how to suppress the thermal-noise flow from the mechanical reservoir is still a difficulty encountered in achieving optomechanically nonreciprocal effects on a few- and even single-photon level. Here, we show how to realize thermal-noise cancellation by quantum interference for optomechanically induced nonreciprocity in a whispering-gallery-mode (WGM) microresonator. We find that both nonreciprocal transmission and amplification can be achieved in the WGM microresonator when coupled to two coupled mechanical resonators. More interestingly, the thermal noise can be suppressed when the two coupled mechanical resonators couple to a common thermal reservoir. The thermal-noise cancellation is induced by the destructive quantum interference between the two flow paths of the thermal noises from the common reservoir. The scheme of quantum-interference-induced thermal-noise cancellation can be applied in both sideband-resolved and unresolved regimes, even with strong backscattering taken into account. Our work provides an effective way to achieve nonreciprocal effects on a few- or single-photon level without precooling the mechanical mode to the ground state.