Photon statistics of the micromaser with ultra cold Λ-type three-level atoms

We have established the master equation for the micromaser with the ultra-cold ii-type three-level atoms and studied the photon statistics of the micromaser field. We find that as the atoms become colder, the change of the mean photon-number and the normalized standard deviation become more regular, and their resonance peaks become sharper. For zero-temperature cavity, there are some regions in which the photon statistics are sub-Poissonian. With the increase of the cavity temperature, both the mean photon-number and the normalized standard deviation increase. When the cavity temperature is high enough, the sub-Poissonian property may disappear.