The Preparation Identification And Application Of Entangled State In Cavity QED System

Entangled state is a foremost research object in quantum information. We can implementquantum communication and quantum computation by the preparation of entangled state in somephysical system. Cavity quantum electrodynamics (QED) is a physical system where quantumentanglement exists. In cavity QED system, Rabi oscillations occur between two-level atom andsingle-mode optical field can achieve the entanglement of atomic state and photon number states.In recent years, the preparation of entangled state in cavity QED system is a hot research topic.Many theoretical schemes about the preparation of entangled states were presented, and someimplementations have been reported in experiment. With the development of cooling andmanipulation of atomic technology, more schemes will be demonstrated in cavity QEDexperiment.Quantum entanglement is a basic resource of quantum communication. Quantumcommunication, Such as dense coding, quantum teleportation and entanglement swapping, is acombination of quantum entanglement and information science. Its absolute confidentiality deeplyattracted us. In quantum communication, recognition to quantum entanglement is crucial. Forexample, we need to accurately identify four Bell states for the performance of a faithful quantumteleportation. How to achieve identification of entangled state is the most critical process ofquantum communication. In the paper, we presented some identification methods for entangledstate, and applied it to quantum communication in cavity QED system.This article summarized in two aspects, of which one aspect is about the preparation ofentangled states, and the another aspect is about the identification of entangled states and itsapplication in quantum communication.1. We have presented our schemes to generate one-dimensional Cluster state and a four-bodyentangled state in cavity QED system. First of all, we have investigated the dynamicsevolutional equation between two-level atoms and the single-mode cavity field. According tothe atomic state evolution, we designed a specific physical model for generating entangled state. In the scheme to generate one-dimensional cluster state, we achieved the preparation of theatomic Cluster state in steps as little as possible via one microwave cavity. Moreover, wedesigned a physical model to generate a four-atomic entangled state which can be exploited afaithful teleportation.2. The identification of the entangled state is essential in quantum communication protocols. Incavity QED system, we presented our methods about the four-body entangled stateidentification and non-destructive and complete Bell-state identification. On the basis ofidentification of these entangled states, we illustrated some quantum communication protocolswhich can be successfully completed in the cavity QED system. In cavity QED system, theidentification of the four-body entanglement which can be exploited a faithful teleportation canbe realized by a physical model. In the process of identification, we exploited the physicalmodels to convert from the four-body entangled state to corresponding product state, so that therealization of identification by the single-atom measurements. In the scheme of non-destructiveand completely Bell-state identification, we proposed a quantum circuit to encode the uniqueinformation of four Bell states into two auxiliary atoms in cavity QED system, in order toidentify Bell states by single-atom measurements for two auxiliary atoms. Bell states can not bedestroyed in the whole process. Therefore, we have achieved non-destruction Bell-stateidentification. This Bell-state identification can be applied in dense coding, quantumteleportation and entanglement swapping. The entangled resource of cavity QED system willnot be decreased after the implementation of these quantum communication protocols.