Investigation Of Quantum Entangled State Analysis And Entanglement Sharing

Quantum information is a new interdisciplinary developed in recent thirty years. It involves a number of scientific researches in the field of physics, information science, cryptography, mathematics and so on. Quantum information mainly contains two branches, quantum computation and quantum communication, both of which consider quantum state as the information carrier and utilize the basic quantum mechanics principles to achieve the computing power and security that cannot be realized by classical computation and communication. Quantum entanglement is a unique phenomenon in the quantum world, without classical counterpart. It is also an important resource, which is widely used in quantum information processing.The photon is considered as the most promising physical candidate for quantum communication in virtue of its high-speed transmission, maneuverability, and so on. The polarization and phase degrees of freedom of photon are often used to encode information. In the past few decades, the researchers have accomplished a lot of quantum communication experiments using the photon as information carrier in both free space and optical fiber. There are four parts of information processing, i.e., the initialization, transmission, manipulation and read-out, corresponding to the preparation, transmission, manipulation and measurement of the information carrier—the quantum state in practical experiment.Quantum state measurement is also called discrimination, is the key procedure to achieve information in quantum information processing. In this paper, a scheme of N-photon polarization GHZ state analysis assisted by the frequency degree of freedom is put forward. We adopt the frequency degree of freedom as the ancillary and the principle of single photon Bell state measurement, to distinguish polarization Bell states and three-photon GHZ states, then generalize it to the situation of N-photon GHZ states. Our scheme can be implemented non-locally with linear optics and a set of mutual orthogonal GHZ state can be distinguished deterministically.Moreover, this paper studies the remote entanglement sharing in long-distance quantum communication. The establishment of quantum entangled channel is the precondition of quantum communication based on entangled state. However, the entanglement and fidelity of the quantum state will be affected by the environment during the transmission. We present an efficient strategy for sharing multipartite polarization entanglement between distant locations via the noisy channel assisted by the time-bin degree of freedom. We use the three-photon GHZ state and W state as examples and then generalize our scheme to distribute arbitrary N-photon polarization entangled state to N distant locations. The remote parties can share the desired state in a deterministic way with 100% fidelity in principle, which makes our scheme useful and practical in long-distance quantum communication.