Unconventional photon blockade with second-order nonlinearity

The photon blockade based on weak nonlinearities is called the unconventional photon blockade. The study of the unconventional photon blockade in recent decades has mainly focused on the ${\ensuremath{\chi}}^{(3)}$ Kerr nonlinearity. In this paper, we study the photon blockade in two weakly coupled nonlinear cavities via ${\ensuremath{\chi}}^{(2)}$ nonlinearity, where ${\ensuremath{\chi}}^{(2)}$ mediates the conversion of a single photon in the cavity with high frequency into two photons with low frequency in another cavity. When the two cavity modes are driven simultaneously, our calculations show that the strong photon antibunching can be obtained in the cavity. The optimal condition for strong antibunching is found by analytic calculations and numerical simulations, and discussions of the optimal condition are presented. The differences between the present scheme and that with ${\ensuremath{\chi}}^{(3)}$ nonlinearity are discussed. This scheme is not sensitive to the change of decay rates, which makes the experimental realization easy.