Squeezing-induced nonreciprocal photon blockade in an optomechanical microresonator.

We propose a scheme to generate nonreciprocal photon blockade in a stationary whispering gallery microresonator system based on two physical mechanisms. One of the two mechanisms is inspired by recent work [Phys. Rev. Lett.128, 083604 (2022)10.1103/PhysRevLett.128.083604], where the quantum squeezing caused by parametric interaction not only shifts the optical frequency of propagating mode but also enhances its optomechanical coupling, resulting in a nonreciprocal conventional photon blockade phenomenon. On the other hand, we also give another mechanism to generate stronger nonreciprocity of photon correlation according to the destructive quantum interference. Comparing these two strategies, the required nonlinear strength of parametric interaction in the second one is smaller, and the broadband squeezed vacuum field used to eliminate thermalization noise is no longer needed. All analyses and optimal parameter relations are further verified by numerically simulating the quantum master equation. Our proposed scheme opens a new avenue for achieving the nonreciprocal single photon source without stringent requirements, which may have critical applications in quantum communication, quantum information processing, and topological photonics.