Entangled State Preparation And Quantum Information Processing In Cavity QED

In recent years, people pay great attentions to the quantum information science. Many quantum information process schemes including quantum cryptography, quantum communication and quantum computation are proposed. Some systems such as ion trap, cavity quantum electrodynamics (QED) and quantum dot can be used to realize the process of quantum information. Due to multi-particle entangled state is a basic resource in the process of quantum information and quantum phase gate is an essential gate for implementing the quantum computation, so it is important to study the physical realization of entangled state and logical gate.At present cavity quantum electrodynamics (QED) is studied earlier,developed faster and promises well. So I decide to study the process of quantum information which bases on cavity QED. The main contents include two aspects: 1. The preparation of entangled state and the sharing of quantum information. 2. The realization of phase gate.1. Based on different cases of the interaction of atoms and cavity field, two methods are proposed to generate a peculiar W-class state. Besides, some entangled states are perfectly teleported with the prepared W-class state as channel. It includes a procedure for the teleportation of an unknown two-particle entangled state (Bell state) and a controlled teleportation scheme of an arbitrary two-atom entangled state in general form. Next, an efficient scheme for sharing an arbitrary three-qubit quantum state with GHZ state as resource is proposed. The advantage is both entanglement resource and operations are less and the receiver can definitely recover the information of three atoms. Last, schemes to generate and deterministically distinguish three important entangled states with two steps and prepare multi-atom cluster state are proposed.2. For the controlled phase gate of three atoms, we consider the effect of cavity decay and atomic spontaneous emission. The analysis of fidelity and probability of success provides a reference about the effect of cavity decay and atomic spontaneous emission to the phase gate. A scheme for realizing a multi-qubit phase gate with one control qubit simultaneously controlling n target qubits in cavity QED system is also proposed. The operation time required for the gate implementation is independent of the number of target qubits. No measurement on the qubits or the cavity mode is needed.