Atomic excitation for a two-level system driven by three input photons

In this paper, the master equations for a two-level system driven by three photons has been derived. Particularly, the incident photons are distributed in two input channels, namely, the first input channel contains a two-photon state, while another single-photon state is in the second input channel. The excitation probabilities of the two-level system are simulated with different bandwidths of input photons. The influence of the number of input photons and channels on the atomic excitation is concluded.