The dynamical behavior of entanglement for excitonsi in two quantum dots placed in a caivty driven by a broadband squeezed vacuum is studied in the low exciton density regime. It is found that the excitions in two quantum dost can evole into a pure entangled state only when the dissipaion of the caivity and exction modes is negligible. When the injected field into the cavity is a squeezed vacuum, the exctions will be in a two-mode Gaussian entangled mixed state even in the long time limit. Analytical expressions are derived, showing the dependece of the entanglement property of the excitons in two quantum dost on the squeezing properties of th inital state prepared in the cavity and the strength of two-photon correlations of the squeezedvacuum injected into the cavity.

Spontaneous emission of an atom with two close upper levels arid one lower level in a multilayer dielectric medium, and quantum interference between transitions form the upper leves to the lower one, are considered. Since the medium is inhomogeneous along the direction normal to tbe interfaces of the dielectric layers, the vancuum had an anisotropic spatial structure, and quantum interference between the two decay channels can appear even if the two dipole matrix elemeats are ortbogonal to each other. If the atom is pLaced in a three-layer dielectric plate cavity, a strong quantum interference interference similar to that for an atom with two nearly parallel dipole moments in free space arises due to the influence of anisotropic of anisotropic vacuum. Putting the atom in a three-layer dielectric waveguide and a one-dimensional photonic crystal, there appears a strong quantum interference similar to that for an atom with nearly antiparallel dipole moments.

A cavity-modified master equaion is derived for a coherently driven, V-type three-level atom coupled to a single-mode cavity in the bad-cavity limit. We show that population iversionin both the bare-and dressedstate bases may be achieved, originationg form the enhancementof the acom-cavity interaction when the caivty are analyzed in terms of the cavity-modifeed transition rates.The atomic fluorescence spectrum and probe absorption spectrum are also investigated, and it is found that the spectral profiles may be controlled by adjusting the cavity frequency. Peak suppression and line narrowing occure under the appropriate conditions.

By means of adiabatically eliminationg the upper level or levels of a A-configuration atom coupling to a two-mode quantized field, we have studied the influencesofac Stark shifts on the atomic coherent population trapping in two important atom-field coupling systems via nondegenerated Raman two-photon processes.The states of the field that trap the atom in its two nondegenerate lower levels are obtained, and the important roles of ac Stark shifts and properties of the atomic upper level or levels in the states of the trapping field in two Raman-coupling systems are also analyzed.

The steady-state populalions and Ihe absorption spectrum of a V-type theree-level atom driven by a strong coherent lield lind a weak slochastic one simultaneously ale ibvestigated. The populaltion inversion in bare-sale and dressed-state bases Can happen significantly due to the effect of tile stochastic field. A relation between tile level gap of both atomic exciled slates and the Rabi frequency is found to decide in which excited state the population is lalger than in another one for the same frequency detuning δ between the coherent and the stochastic fields. The line profiles of the absorption spectrumare strognly dependent on the frquency detuing δ, Different lineshapes such as a sharp emission peak (gain). an absorption peak or a dispersion-like peak can be exhibited al the line centre for differentδ. Asymmetrical spectral features and line narrowing can be reached by adjusling δ and the Rabi frequency. Plobe gain in sidebands can occur due to the unbalanced populalion distribuitn in dressed states.