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.

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.

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.

The dynamical behavior of entanglement ofr excitons in two quatum dots placed in two separately singlemode optical cavities driven by an external boradband two-mode squeezed vacuum is studied in the low exciton density regime. It is found that if the field in the two separated cavitied is initially prepared in a pure two-mode squeezed vacuum state, the excitons in the two quantum dots cna evolve into a pure entangled state only when the dissipation of the cavitied and excition modes is negligible. When the efect of the dissipation is included, the excitions will be in a two-mode Gaussian entangled mixed state whose properties are decided by the externally driven fiedld and the initial field. The dependence of the entanglement property of the excitons in the two quantum dots on the squeezing properties of the fields in the two cavities is also discussed.

The generation of an entangled state for a pair fof two-level atoms embedded in a bad cavity injected with a squeezed vacuum is investigated. The degree of entanglement between the two atoms strongly depends on the mean photon number and the strength of two-photon correlations of the squeezedvacuum, the cavity-induced decay rate of atoms, and the atomic separation.