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

The semiclassical model of atomfield 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 fullquantum electrodynamics formalism, where the probe and coupling electromagnetic fields are quantized. in this article, we investigate the fullquantum model of absorption and dispersion spectrum of trapped fourlevels inverted y type atoms, interacting with a probe beam of photons as well as twomode 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 twomode coupling photons, individually. an experimental setup for this nondemolition photon counting method is proposed and the numbers of coupling photons are obtained analytically.