Study On Continuous Variable Quantum Key Distribution Using Coherent States

From ancient times to the present, information security is an very important aspect of the communication research. In modern cryptography, it is believed that any algorithm of encryption and decryption in cryptographical systems can be open, their safety depends on key security. However, due to the presence of eavesdropping, in the classical communication, it is impossible to establish unconditional security key. Quantum Key Distribution(QKD) is able to detect the eavesdropping and can provide an unconditional secure key distribution program.Although the study of quantum key distribution using single-photon is relatively mature, it is difficult to prepare reliable single-photon sources or high-detect-efficiency photon detectors at present. In contrast, continuous-variable QKD (CVQKD) schemes typically use quadratures of light beams as information carriers and homodyne detectors., so it is technically easier to achieve. At the same time, it is compatible with the existing communications systems. As a result, the subject has raised a concern of the researchers and become a focus in quantum communication research.In this article, the basic principle related to coherent state CVQKD is described in detail. And theoretically calculate the impact on the key security due to excess noise which is introduced by unideal of source characteristics and other reasons. Secondly, we simulate the coherent state CVQKD from the theoretical, including quantum channel communication process and reverse reconciliation in classical channel. Finally, several issues on the realization of CVQKD were simply explored.