We investigate the spontaneous-emission properties of a two-level atom embedded in a three-dimensinal anaisotropic photonic crystal. In addition to the modified density of states, the atom is driven by a coherent intense lowfrequency field (LFF), which creates additional multihoton decay channels with the exchange of two low-frequency photons and one spontaneous photon during an atomic transition, Due to the ow frequency of the appliced field, the various transition pathways may interfere with each other and thus give rise to a modifeed system dynamics. We find that even if all the atomic(bare and induced) transition frequencies are in the conducting band of the photonic crystal, there still mya exist a photon-atom bound state in coexistence with propagating modes. the system also allows us to generate narrow linesin the spontaneous-emission spectrum. This spectrum is a funcion of the distance of the observer form the atom due to the band gap in the photonic crystal. The system properties depend on three characteristic frequencies, which are influenced by quantum interfernce effects. Thus these results can b attributed to a combination of interference and band-gap effects.

The decay and radiation of an atom in a photonic crystal with an incomplete gap was investigated. If the transtition frequency is close to a band edge, the Weisskopf-Wigner approximation is not applicable and the decay is nonexponential. The decay could be greatly enhanced or decreased by the self-emitted field.

In this paper, we have investigated the time evolution of |he phase operator of the radiation field in the Jaynes-Cummings model with and without tfie rotating-wave approximation, making use of the phase formalism of Barnett and Pegg [J. Mod. Opt. 56, 7 (1989); Phys. Rev. A 39, 1665 (1989)]. We verify by an analytical method that the atomic Rabi oscillation leads to phase dissipation of the radiation field, and also that the effect of the virtual-photon field can exhibit quantum fluctuations in the atomfield-coupling system and lead to a Frequency shift of the radiation field.

We investigate the effect of the dipole-dipole interaction on the dynamic properties and the atomic coherent trapping of a two-identical atom system in the presence of a laser field by means of quantum electrodynamics theory, The influence of the dipole-dipole interaction on the collapses and revivats of the atomic population is revealed. The conditions of the atomic eoherent trapping are given. A way to measure optically the coupling strength between the atoms is pointed out. Wc also show that the cffect of the dipole-dipole interaction may be screened duc to the coherent field in certain atomic superposition states.

In this paper, we have investigated the influence of the cvunler-rotating terms on the squeezing of light in the two photon layaes-Cummings mcodel by means of the nonrelativistic QED. We verified that the effect af the virtual-photon field increases the squeezing. The relations between the degree of squeezing and the frequency of field, the mean photon number, and the atom-field coupling constant have alsp been analyzed.