Linear Optics And Quantum Entanglement

Since the nineties of the 20th century, quantum information science, which mainly includes quantum computer and quantum communication, has increasingly evolved as a new object. Because the carrier of information in this subject, all the problems related to information should be resolved by means of quantum theory. Therefore, quantum information science exhibits a number of advantages corresponding to classical counterpart. Such as, based on the correlated superposition of quantum states, scientists have developed quantum parallelism arithmetic, which could be used to resolve efficiently some hard problems such as factorization of large numbers and the simulation of complicated quantum systems. In addition, the existing of quantum non-cloning theory leads to the birth of quantum cryptograph. Quantum cryptograph can in principle provide a safest communication system that is unassailable and not wiretapped. Quantum communication is a important branch of quantum information science, mostly involving quantum teleportation, quantum dense coding, quantum secret share, quantum key distribution, and so on.In 1935, Einstein? Podoscky and Rosen brought forward the Famous EPR correlation. Since then the concept of quantum entanglement state was given birth to. Entanglement is one of the most striking features of quantum mechanics, and plays key pole in all fields of quantum information science. Entanglement states provide not only the possibility to test quantum mechanic against local hidden theory. They also lead to practical application in the field of quantum information. Meanwhile, these applications motivated an intensive research in the generation and manipulation of the quantum entanglement because of the key rule in the application of quantum information.Beam splitter is a kind of linear optic device, easy and available, acting as anentangler. It could entangle the output states under a certain condition. In this paper, we mainly investigate the generation of quantum entanglement by injecting odd and even coherent states into lossless beam splitter, and the projection measurement of the entangled output states generated by beam splitter. The main contents of this thesis are as fellow:1. The application of even and odd coherent states in quantum information is studied. When vacuum state is injected into one input port while odd coherent state is injected into another, quantum entanglement is generated at the output ports. The measurement of this quantum entangled state is almost equal to that generated when vacuum state and even coherent state injected, which shows that the generation and measurement of quantum entanglement is mainly depended on the nonclassicality of the input states. When arbitrary even or odd coherent states are injected into both of separate input ports, there will be more complicated quantum entanglement at the output ports.2. We study the projection measurement of the entangled output states generated by beam splitter. First, when we inject vacuum state into one input portwhile odd or even coherent state is injected into another, we set a photon detectorat c output port. We find: if we get even number photons at c output port, the output state at d output port possesses the same property as the input state's. If odd number photons, the output state is reversed. That is, even coherent state is output when odd coherent state injected, and odd coherent state is output when even coherent state injected. Second, we inject single photon state "and even or odd coherent state into beam splitter. Then the squeezing and photonanti-bunching effect of d output state is studied and analyzed.