Reverse Reconciliation For Continuous Variable Quantum Key Distribution

Quantum key distribution (QKD) is a new branch of information security field and an interdisciplinary subject of quantum theory and classical information. Based on the basic principles of the quantum physics, for example the uncertainty principle and the quantum no-cloning principle, any eavesdropping attacks can be detected and the unconditional security communication between two legal parties can be achieved. The past few years have seen significant progress in both the QKD theoretical and experimental research, and QKD has already become a research focus in the field of quantum information and secure communication.Continuous variable (CV) QKD systems can utilize the stable and mature light sources (for example, coherent state light field) and the quantum states can be measured via the homodyne detection efficiently. The measurement results are robust against the background field noises, furthermore, the bandwidths of the detectors can be above GHz or more and the corresponding quantum efficiencies can reach90%, which result in the great improvement of the security key rate. The advantages and potentials of the continuous variable QKD have attracted extensive attentions from researchers and both the theory and experiment have made great breakthroughs recently. Reconciliation is an essential and important process in the continuous variable QKD system, whose purpose is to extract the security key sequence from a set of related data between Alice and Bob. The security, efficiency and speed of the reconciliation will directly affect the amount of security key information between two parties.In this paper, reverse reconciliation of the continuous variable QKD was investigated in detail. Firstly, I show how to select the optimal quantization intervals by maximizing the mutual information between the two communicating parties. Then the optimal rate of each equivalent channel is calculated at a SNR level of4dB. The low-density parity check (LDPC) code is chosen as the channel codes. By utilizing a side-information based LDPC iterative decoding algorithm, we successfully realized the reverse reconciliation process of CV coherent state QKD.