| Entanglement, which is the central resource of quantum information processing and quantum computation, has been extensively used to test quantum non-locality and design quantum information protocols, such as Greenberger-Horne-Zeilinger (GHZ) state, Wstate, Cluster state and so on. Entanglement plays an important role in quantum information. GHZ state can maximally violate Bell-type inequalities and is maximally stable against white noise. W state is not maximally entangled, but it is robust against the loss of one qubit. Cluster state, which can be regarded as a resource of GHZ state, is very important for one-way quantum quantum com-putation, therefore it is very important to generate entangled states.At the beginning, we introduce the basic knowledge of entanglement and quan-tum information and its applications in quantum information processing. Then, we present the basic theories of quantum non-demolition (QND) measurement and cross-kerr nonlinearity that provide a good tool to construct quantum non-demolition (QND) devices, which has the potential of being able to evolve our system without destroying the single photons. Our thesis focuses on research of a four-photon en-tangled state, which is equivalent to a four-particle Cluster state under local unitary transformation. What’s more, it can be regarded as a resource of two-qubit tele-portation. Thus, it has possible applications in quantum information processing. In this discussion, we recommend a device using the weak cross-Kerr nonlinear-ity system which can create a maximally two-qubit entangled state, ie., Entangler. Then, we got3maximally states. Besides, we entangled photon3and4via a45°-Entangler. Finally, we detected photon3and did the corresponding unitary transformations. Therefore, we can get a four-photon entangled state with a nearly deterministic success probability. Compared with other schemes, this scheme has much higher success probability and simple structure that is feasible under current experiment condition. |
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