Based On Secure Communications And Multi-particle Part Of The Single-photon Entangled State Research And Applications

The purpose of secure communication is to let both sides of communication exchange information and not allow any illegal third party to steal or destroy the content of information. In order to achieve this purpose before appearance of public key cryptography what people used is the private key skill which depends on keeping the key, code rule and key transmission secret to guarantee security of communication. But the main difficulty of the private key cryptography is the secure distribution of the key. Especially, Vernam cryptogram is the only one proved a definitely safe cryptography and achieve the security "one key used only once", but it is too huge to be used in practice. One of the earliest discoveries of quantum computation and quantum information is that quantum mechanics can be used in key distribution because the Heisenberg uncertain principle has offered a feasible way.Quantum entanglement is considered to be a kind of basic physics . resource in quantum mechanics. As to a complex system composed of N subsystems, if the density matrix of it can not be written in the direct product linearity sum form of the density matrix of every subsystems, then the complex system is entangled and the state of the system is entangled. Recently, people are deeper to realize that quantum entanglement plays a very important role in quantum computation and quantum communication.We mainly research on two aspects of quantum secure communi- cation and application of the nonmaximally entangled state in this article. Due to the decoherence caused by the interaction between environment and quantum channel, the quantum channel will not keep the maximally entangled state at this moment. In chapter three of this article, we investigate the probabilistic teleportation based on non-maximal entanglement. In chapter four of this article, we put forward a quantum key distribution and secure communication scheme using single photon states which are non-conjugate to each other between two parties. Relative to other congener schemes, this scheme is more efficient. In chapter five of this article, we proposed a new controlled quantum key distribution protocol by utilizing four-level particles entanglement which could be regarded as concrete application of the controlled quantum teleportation.