Star Cluster State And Preparation Of Bound Entangled State Of Optical Field

Quantum entanglement is widely and deeply researched as the main resource of quantum computation and quantum information system. Multipartite entanglement is the basic quantum resource to develop quantum computation and quantum information networks. It has been shown that there are kinds of multipartite quantum entangled states with different physics construction and features, the wave functions and quantum inseparability criteria of them are different.As a special multipartite entangled state, cluster entangled state is the basic resource for one-way quantum computation. One-way quantum computation use the prepared cluster states as basic resource, and perform computation by measuring some quantum qubits (qumodes) and feedback measured result. Up to now, the maximum-partite of experimentally prepared continuous-variable cluster entangled state is four-partite, and a series of quantum logical operation has been realized based on it, such as single-mode squeezing operation, Fourier transform, control-X operation, control-Z operation and so on. But for realizing quantum computation, a series of quantum logical operation need to be performed continuously, which can not be completed with four-partite cluster entangled state. So, even more-partite cluster state is needed to be prepared experimentally.The decoherence owing to unavoidable loss in experimental system, entangled states become mixed states easily. It is important to study the character of mixed entangled state and know whether maximally entangled states can be distilled from it, and apply it to quantum information research. Bound entangled state is a special entangled state between separable and free-entangled state from which no pure entanglement can be distilled by local operation and classical communication. But it can be activated by some way and applied to quantum teleportation system.The main contents of this thesis are as following: 1. Generation schemes of continuous-variable six-partite and eight-partite star cluster entangled states based on non-degenerated optical parameter amplification are designed. The calculation result shows that some initial squeezing is needed when the gains are1in order to prepare star cluster state; but the limit of squeezed degree can be overcome with the optimal gain factor.2. We experimentally prepared continuous-variable four-partite bound entangled state. The measured correlation variance of four-mode bound entangled state, xb1+xb2+xb3+xb4and pb1+pb2-pb3-Pb4are5.2±0.1dB below the corresponding quantum noise level, respectively, and it’s proved that the prepared state can not be distilled by local operation and classical communication.