“…2 is detuning. Thus, the single photon blockade could be realized in this system with the optimal condition D = + W g , 2 2 as obtained in equation (10a). there are different transition paths to reach the two-photon state of mode a, for example, the direct path, i.e., ñ | g 0, 0, 0, ñ | g 2, 0, 0, , the path through the atom, i.e., ñ…”