Probabilistic Teleportation And Entanglement Swapping Via Cavity QED

Quantum information science mainly including quantum computation and quantum communication is a new subject combining quantum mechanics and information science. In order to realize quantum information processing, we need to build some quantum hardwares that enable us to manipulate qubits. Note that cavity QED is designed as one of optimal candidates for achieving quantum information processing such as quantum teleportation, the preparation and manipulation of the entangled states, the realization of quantum logic gates, and so on. With the experimental developments concerning cavity QED, it is necessary to further study various schemes for quantum information processing in theory. In this thesis, we focus our research on the applications of cavity QED to entanglement swapping and quantum teleportation.Based on the technique of cavity QED and entanglement swapping, we propose an entanglement swapping and concentration scheme without joint measurement using a two-photon Jaynes-Cummings model. By means of entanglement swapping, firstly we get a nonmaximally entangled pair between an atom and a cavity mode which previously have not any interaction with each other. Then we consider two cases for conditional entanglement concentration. One case needs an additional atom initially in its ground state while the other case needs an extra cavity initially in the vacuum state. The two schemes of entanglement concentration can be achieved with the former leading to a maximally entangled state of two atoms and the latter to a maximally entangled sate of two cavities. The distinct feature of the scheme is that we can obtain an entanglement of two photons in one cavity and zero in the other one.Based on the technology of cavity QED, we propose a probabilistic teleportation scheme for a two-atom entangled state and for a three-atom entangled state, respectively. A three-atom partially entangled state is used as the quantum channel for probabilistically teleporting a two-atom entangled state. Teleportation of the two-atom state can be achieved with thermal cavities with the assistance of a strong classicaldriving field. Moreover, by adding an additional resonant cavity, teleportation of the two-atom state can also be realized and the corresponding success probability of teleportation can be improved. Using a quantum channel composed of a two-atom and a three-atom nonmaximally entangled states, the teleportation of a three-atom GHZ class state can be respectively realized with the large-detuned vacuum cavities and with the thermal cavities. The advantages of our schemes are that partially entangled state is used as quantum channel, so it is unnecessary to concentrate nonmaximally entangled quantum channel in advance. During the process of the atoms through the cavity, there is no transfer of quantum information and energy between the atoms and the cavity, thus the efficient decoherence time of cavity is greatly prolonged. The joint Bell states measurement is replaced by separate atomic measurements.