Twofold Information Reconciliation Based on Polar Codes for CV-QKD

Continuous variable quantum key distribution (CV-QKD) enables authenticated parties to share a key. Information reconciliation (IR) is a critical step of the post-processing in CV-QKD, significantly affecting the secret key rate (SKR) shared between the legitimate parties. To improve the SKR performance of the CV-QKD without increasing the key inconsistency rate (KIR), this paper proposes a twofold IR method by performing independent operations on the Gaussian modulated coherent states (GMCS) obtained over the quantum channel. Specifically, assuming reverse reconciliation, after the GMCS are quantized, Bob generates parity bits, which are shared with Alice to help her correct the inconsistent bits in the quantized bits to generate the partial key. At the same time, the parity bits are used as frozen bits of polar codes in the multidimensional reconciliation (MR) to generate the other partial key. Simulation results demonstrate that the proposed twofold IR method increases the SKR nearly twice without increasing the inconsistent bits. In addition, we propose to apply symbol expansion and rotation (SER) based on the mapped GMCS to reduce the amount of information to be transmitted over the public error-free channel. Simulation results demonstrate that the performance of the proposed twofold IR with SER method can achieve a higher SKR with 3dB performance gap to that of the traditional MR protocol.