Generation of sub-Poissonian photon statistics in a two-level atomic oscillator

According to the exact solution of a two-level atomic system interacting with a single-mode field in a cavity and including a pumping mechanism, sub-Poissonian photon statistics can be generated either by regular pumping or by resonance absorption of the lower level. When the atomic lifetime is much smaller than the interaction time (${\gamma }_{\mathit{a}\mathit{b}}$τ≫1), which corresponds to a usual laser system, the sub-Poissonian photon distribution can be obtained only by regular pumping. On the other hand, if the atomic lifetime is comparable with the interaction time (${\gamma }_{\mathit{a}\mathit{b}}$τ≤1), the sub-Poissonian photon distribution can be generated by both mechanisms.