Collective Switching and Inversion without Fluctuation of Two-Level Atoms in Confined Photonic Systems

We demonstrate population inversion and sub-Poissonian excitation statistics of $N$ two-level atoms in the context of collective resonance fluorescence. This occurs within photonic band gap and other confined photonic systems that exhibit sharp features in the optical density of states. When the deviation in the photon density of states between the Mollow spectral components is considerable, the atoms switch collectively from ground to excited states at a critical value of the applied laser field. This suggests a new mechanism of sub-Poissonian pumping of lasers, fast optical switching, and optical transistor action.