Photon Blockade — Kerr Nonlinear Cavity

En = nωc + n(n−1)U/2  |  Anharmonic ladder blocks two-photon absorption

U/κ
g²(0)
Blockade
g²(0) < 1: sub-Poissonian
g²(0) = 0: perfect blockade
g²(0) = 1: coherent state