Squeezed single-atom laser in a photonic crystal
  We study non-classical and spectral properties of a strongly driven single-atom laser engineered within a photonic crystal that facilitates a frequency-dependent reservoir. In these studies, we apply a dressed atom model approach to derive the master equation of the system and study the properties of the dressed laser under the frequency dependent transition rates. By going beyond the secular approximation in the dressed-atom cavity field interaction, we find that if, in addition, the non-secular terms are included into the dynamics of the system, then non-linear processes can occur that lead to interesting new aspects of cavity field behavior. We calculate variances of the quadrature phase amplitudes and the incoherent part of the spectrum of the cavity field and show that they differ qualitatively from those observed under the secular approximation. In particular, it is found that the non-linear processes lead to squeezing of the fluctuations of the cavity field below the quantum shot noise limit. The squeezing depends on the relative population of the dressed states of the system and is found only if there is no population inversion between the dressed states. Furthermore, we find a linewidth narrowing below the quantum limit in the spectrum of the cavity field that is achieved only when the secular approximation is not made. An interpretation of the linewidth narrowing is provided in terms of two phase dependent noise (squeezing) spectra that make up the incoherent spectrum. We establish that the linewidth narrowing is due squeezing of the fluctuations in one quadrature phase components of the cavity field. 
Rong Tan, Gao-xiang Li and Zbigniew Ficek