Asymmetric synchronous single-photon blockade induced by parametric interactions

We propose a scheme to achieve asymmetric synchronous photon blockade (PB) in a system composed of two optical cavities coupled through a nonlinear crystal. By regulating the input direction of the pump light, either single-cavity PB or two-cavity synchronous PB can be selectively realized based on the incidence direction. This asymmetry arises from parametric up- and down-conversion processes induced by the pump light incoming from opposite directions. The delayed correlation function further demonstrates the high temporal resolution of the synchronized single photons generated in both cavities. This scheme enables flexible control over different types of PB by simply tuning the pump direction, without any modifications to system components. Moreover, the two-cavity synchronous PB mechanism provides an efficient approach for single-photon heralding, holding the potential to surmount the commonly encountered issue of low collection efficiency in probabilistic single-photon sources.