Narrow Results

We study the interaction of a moving four-level atom with a single mode cavity field. Involving intensity dependent coupling, the atom-field wave function and the reduced density matrix of the field are obtained when the atom is initially prepared in a coherent superposition of the upper and ground states and the field is initially in a coherent state. The influence of the intensity dependent atom-field coupling and of the detuning on the collapse and revival phenomenon of the time evolution of statistical aspects, such as the mean photon number, the second-order correlation function of the field, the momentum increment and momentum diffusion, are investigated. It is found that, for the nonresonant case, the detuning between the field and the atom has a significant influence which leads to increasing the collapse time with decreasing amplitude. Numerical computations and discussion of the results are presented.

We propose a scheme for entanglement swapping and entanglement concentration without joint measurement by using the two-photon Jaynes-Cummings model. In the scheme, we can generate a maximally entangled pair between two initially uncorrelated atoms or cavities. Furthermore, the entangled state between two cavities is found to be a photon entanglement of two photons in one cavity and zero in another cavity.

We present two schemes for probabilistically teleporting a two-atom entangled state using a three-atom partially entangled state as the quantum channel in cavity QED with the help of separate atomic measurements. The first scheme is only based on the interaction between two driven atoms and a quantized cavity mode in the large detuning limit, so the effects of both cavity decay and the thermal field are eliminated. In the second scheme, it is necessary to introduce an additional resonant cavity besides the thermal cavity to realize the teleportation, and the corresponding success probability is improved.

In this paper, we propose an entanglement concentration protocol for unknown tripartite W class states via the detection of photons which are leaked out from the cavities. In our scheme, the atom-cavity coupling strength is smaller than the cavity decay rate. Hence, the requirement on the quality factor of the cavities is greatly relaxed. The scheme is for nonpost-selection results and the fidelity of the scheme is not affected by the detection inefficiency and atomic decay. All the processes are within the current technologies.

Quantum mechanics allows one to encode the information in the superposition of a quantum state which embodies the nature of quantum nonlocality. Here we propose a realizable physical scheme for a multiparticle quantum dense coding (QDC) between two users in cavity quantum electrodynamics (QED). We also discuss the feasibility of our scheme within current technology.