Photon Entanglement And Quantum Communication

This dissertation discusses the quantum information fundamentals and its realization by linear optics approach, the content of which covers the technique of generating entangled photons by spontaneous parametric down-conversion process, as well as method of manipulation and measurement of single photon. It also presents a brief overview of the development of quantum information.Realistic linear optical quantum information processing necessitates the ability to synchronously generate entangled photon pairs either at the same or at distant locations. This dissertation discusses the experimental realization of synchronized generation of independent entangled photon pairs. The quality of synchronization is confirmed by observing a violation of Bell's inequality with 3.2 standard deviations in an entanglement swapping experiment. The techniques developed in the experiment will be important for future linear optical realization of quantum communication and computation.In the experiment of BB84 quantum key distribution (QKD) in decoherence-free subspace (DFS), it is demonstrated that a good key rate can be realized even with a large bit-flip error rate caused by collective rotation, showing the potential application of DFS in future free-space quantum communication.Time-Energy entanglement is another type of entanglement, which plays an important role in quantum communication over optical fiber. The dissertation here, propose a new scheme for generating time-bin entanglement based on post-selection technique. It is shown that the approach proposed here can be exploited in the experiment for testing quantum nonlocality. Moreover, using this approach, a hyper-entanglment was implemented experimentally.