Optical Communication Systems Using Quantum State Control

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This research is classified as the field of the quantum communication which has been studied by Yuen, Helstrom, and Hirota since 1974. In this research, we have clarified many new results for high quality optical communication system by using quantum state control which was proposed by Tamagawa University in 1988, and has been developed by Keio University, Tamagawa University, Tokyo Inst.Tech. and Yamanashi University since 1990. This project has been accomplished as a research cooperation between Keio University and Tamagawa University. As a result we have obtained the following results.1. Properties of degenerate parametric amplifier and optical bistability were investigated. As a result, we showed conditions of generation of squeezed light and squeezing the quantum noise over wide bandwidth of them.2. When the light with quantum state control is transmitted, its superior properties are destroyed by the transmission loss. Therefore the degradations of system performance should be clarified with respect to the degree of loss. We showed that the performance of the systems using the quantum state controlled light is superior to the standard quantum limit with any amount of loss.3. We showed some examples of the received quantum state control systems which has been proposed by Hirota4. We investigated the properties of the conditional unitary process which was defined by Hirota and showed that the linear attenuation process is one of the examples.5. In order to realize the received quantum state control, the reduction of the inner product of the input quantum states is required. It was pointed out that the nonlinear beamsplitter is one of examples of the reduction phenomena of the inner product.6. Some modulation schemes of squeezed light were proposed for optical communication and measurement systems. Their spectrum transformations through the modulations were derived. The optimum condition for modulation was also given.