Study on application of polar codes to information reconciliation in free-space quantum key distribution

Quantum key distribution (QKD) is a technology to securely share keys against any attack physically permitted, with the principle of quantum mechanics. In recent years, the satellite QKD, which employs artificial satellites as trusted mobile nodes, has been attracting attention in order to overcome the bottleneck of transmission distance. However, in the satellite QKD, quality degradation due to atmospheric effects is expected, as in ordinary satellite laser communications. Therefore, it is desirable to apply an error-correcting code (ECC) that has high error-correcting performance even under the atmospheric-induced effects to the error-correcting process of the satellite QKD. Therefore, in this paper, we examined the application of polar codes, which is known as an ECC with high error correction capability. First, in order to optimize the error correction efficiency, we propose a method to adaptively obtain an appropriate code rate for the received signal strength that changes momentarily due to atmospheric effects. Then, we compare the throughput performances with polar codes to it with low-density parity-check (LDPC) codes, with the numerical simulation assuming Bennett-Brassard 1984 protocol (BB84).