Nonreciprocal photon blockade in cavity optomagnonics

We study nonreciprocal photon blockade in cavity optomagnonics, where a sphere of ferromagnetic crystal supports two optical whispering-gallery modes and one magnon mode. The interaction in cavity optomagnonics is subject to the selection rules involving conservation of angular momentum and energy, and the selection rules introduce a nonreciprocal coupling between linearly polarized photons and magnons. For given incident linearly polarized photons, the photon blockade occurs when the cavity is driven in one direction, but it disappears if the cavity is driven in the opposite direction. The results suggest that cavity optomagnonics could be a promising platform for studying chiral quantum optics and topological photonics.