Quantum Channel Coding And The Theory Of Quantum Cryptography Research

The combination of quantum mechanics and classical information theory yields the new subject of quantum information theory. Quantum mechanics is the foundation of quantum information,which primarily study quantum information processing,including quantum computer,quantum communication and quantum key distribution. When we applied the properties of quantum mechanics to information,classical limit of information theory could be exceeded in many ways,and we can accomplish many unimaginable tasks for classical information processing,such as fast factoring,tele-portation,absolutely secure cryptograph etc. The naissance of quantum information provided with reliable physical foundation for future revolution of information as well as new principle and method for development of information in 21 century.One obstacle that quantum computation,quantum communication and quantum key distribute must combat is noise. In quantum system,noise primary results from decoherence and imperfect quantum gates. The code that combat noise is named quantum channel coding. Both quantum error correcting code and quantum error avoiding code are practical quantum channel coding schemes. We present in this dissertation a new quantum error correcting code scheme,named serially concatenated quantum convolutional code. We first design the construction modules of serially concatenated quantum convolutional code. And then design the corresponding code-coding gate-array. In quantum error avoiding code,we first unified the definitions of decoherence-free subspace,and then proved that all these definitions are equivalent. We also proposed a simple method to compose decoherence-free subspace utilizinggroup theory.Quantum key distribution is the first quantum information application that is nearly applicable. Both BB84 and B92 have been achieved great success in experiments. The study on unconditional security of quantum key distribution scheme is relatively lag behind. Unconditional security of BB84 had been proved quite recently. We present the general principle how to prove the unconditional security of a quantum key distribution scheme. Meanwhile the unconditional security of B92 protocol was proved according to our principle. Furthermore we analyzed optimal condition that we should subject to when selecting parameters for B92 protocol. When biased B92 protocol being adopted,and when two states satisfying certain condition,we can obtain an optimally performed B92 scheme.