Tunable nonreciprocal photon correlations induced by directional quantum squeezing

We investigate nonreciprocal photon correlations in coupled microring resonators with directional quantum squeezing (quantum parametric amplification). We show that the degeneracy of two whispering-gallery modes (WGMs) in a microring resonator are broken by applying parametric amplification to one of the WGMs, which makes tunable chiral photon-qubit coupling and chiral photon hopping between two resonators feasible. Selecting optimal quantum squeezing strength, we predict the appearance of nonreciprocal unconventional photon blockade resulting from the interferences among different photon transition-dissipative paths both analytically and numerically. Moreover, flexible conversion between photon bunching and antibunching can be easily realized in a wide range of parameter regimes by modulating the quantum squeezing field. This work provides an alternative way for tunable nonreciprocal photon coherence manipulations in chiral quantum science and technologies.