Nonreciprocal unconventional photon blockade in atom-cavity with χ(2) nonlinear medium

In this paper, we show that the photon blockade (PB) can be observed in a nonreciprocal way with a driven spinning atom-cavity coupled filled with [Formula: see text] nonlinear medium. We analytically derive the optimal conditions for strong photon antibunching, which are in good agreement with those obtained by numerical simulations. Under the weak driving condition, we discuss the physical origins of the nonreciprocal unconventional photon blockade (UPB), which originates from the destructive quantum interference between different paths from the ground state to two-photon states by driving the device from the left side. While the quantum interference paths are broken when the device is driven from the right side, which leads to the occurrence of the photon bunching. Moreover in the opposite direction of driving the device, we also observe another nonreciprocal UPB effect, which can occur by generating bunching and antibunching effects via driving the device from the left and right sides under the derived optimal conditions, respectively. Finally, we cannot observe the nonreciprocal UPB phenomenon with the large cavity decay compared to the atomic spontaneous emission rate (or the bad cavity limit), and give the physical reason behind it. Possible experimental implementation for this scheme is presented.