Multiedge-type low-density parity-check codes for continuous-variable quantum key distribution

Continuous-variable quantum key distribution utilizes an ensemble of coherent states light to distribute secret encryption keys between two parties. One the challenges is thereby requirement capacity approaching error correcting codes in low signal-to-noise (SNR) regime (SNR < 0 dB). Multilevel coding (MLC) combined with multistage decoding (MSD) can solve this challenge combination multi-edge-type low-density parity-check (MET-LDPC) which are ideal for code rates SNR due degree-one variable nodes. However, complexity designing such highly efficient remains open issue. Here, we introduce concept generalized extrinsic information transfer (G-EXIT) charts MET-LDPC and demonstrate how tool be used analyze their convergence behavior. We calculate each level MLC-MSD scheme use G-EXIT exemplary find some given provide a better threshold compared previously reported codes. In comparison traditional density evolution method, offer simple fast asymptotic analysis