a non-demolition photon counting method by four-level inverted y-type atom

the semi-classical model of atom-field interaction has been fully studied for some multilevel atoms, e.g. vee, l, cascade x , y, and inverted y and so on. this issue is developed into the full-quantum electrodynamics formalism, where the probe and coupling electromagnetic fields are quantized. in this article, we investigate the full-quantum model of absorption and dispersion spectrum of trapped four-levels inverted y type atoms, interacting with a probe beam of photons as well as two-mode trapped coupling photons. it is shown that the measurement of the maximum of absorption of the probe field and its detuning gives us simply the number of two-mode coupling photons, individually. an experimental setup for this non-demolition photon counting method is proposed and the numbers of coupling photons are obtained analytically.