Generation And Application Of Optical Quantum Entanglement States

In the quantum information science, quantum entanglement plays an important role. Thank to its nonlocality and other special properties, it enables higher speed performance, more powerful communication, more secure communication, etc., compared with the classical information science. It becomes an important resource in the area of quantum information, and how to create quantum entanglement is therefore becoming a hot topic. There are many kinds of entangled states. Their rich structures result in the difficulty of generation. The generation of one kind of entangle state is hard to be developed to another kind of entangled state generation. We have to develop many and many approaches for the entangled states generation.In this paper, using the technology of linear optics and the cross-phase modulation, we firstly present a simple scheme for adding independent single photos to the existed W state. We can efficiently add one or more than one independent single photons with the help of a CNOT and a discrimination process. The size of W state will be expanded as considered. Specifically, we can expand the n-photon W state to be the n+1-photon W state with the success probability (n+l)/2n, which can be increased with the further operations. In addition, by m CNOT operations and a complicated discrimination, the m independent single photons can be added the existed W state simultaneously.Secondly, we present a scheme to generate universal weighted graph state. With the cascade CZθ operation, the entanglement bonds between dependent or independent single photons can be created efficiently with only one ancilla single photon. The generation is scalable for universal weighted graph states, including arbitrary two-dimensional or three-dimensional weighted graph states. Moreover, the generation is flexible, including that the controlled phase shift θ between each pair of single photons can be different, the traces of the ancilla single photon walking is not fixed, and the prior entangled states are not required.In one word, we present two schemes to expand W state and generate universal weighed graph state. The generated entangled states can be conveniently used to many tasks of quantum information, and with them one can investigate the properties of quantum entanglement and operation the entangled states much conveniently.