Study On Continuous Variable Quantum Key Distribution

According to the basic theories of quantum mechanics, Quantum Key Distribution(QKD) can provide a means of unconditionally secure communication between two distant parties, Alice and Bob, against a potential eavesdropper-Eve. Early QKD setups use so-called discrete variables, therefore requiring single-photon sources and detectors. However, 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 rather than photon detectors. Such protocols eliminate the need for single photon technology, as they only require standard available telecom components, such as diode lasers, electro-optic modulators, and PIN photondiodes. At present, CVQKD schemes have become one of the hotsports in the field of quantum information science.However, CVQKD protocols require more complicated classical error correction algorithms, that is reconciliation algorithms, to efficiently extract secret bits from correlated continuous variables between Alice and Bob. In theory, best reconciliation algorithms base on coded modulation techniques with LDPC codes, whose performance could be extremely close to the best possible as determined by the Shannon capacity formula.In this paper, we first give the physical parameters that affect the security of a practical quantum key distribution system, and then discuss what conditions a secure reconciliation algorithm needs to meet with these parameters. Finally, we describe in detail on the design of a secure reverse reconciliation algorithm with LDPC codes, whose efficiency reaches 0.89.