High-speed reconciliation with convergence-based early termination for CV-QKD using SC-LDPC codes

Area of Science:

• Quantum Information Science
• Quantum Cryptography
• Information Theory

Background:

• Information reconciliation (IR) is crucial for continuous-variable quantum key distribution (CV-QKD) to achieve high secret key rates and long distances.
• Improving IR efficiency and addressing the low-density parity-check (LDPC) decoding speed bottleneck are key research challenges in high-speed CV-QKD.

Purpose of the Study:

• To propose a construction scheme for spatially coupled (SC) LDPC codes in CV-QKD systems that maintains a constant code rate with flexible code length.
• To investigate the relationship between syndrome variation patterns (SVP) and frame error rate.
• To develop an adaptive decoding strategy, the convergence-based early termination (C-ET) scheme, to reduce decoding latency and improve efficiency.

Main Methods:

• Proposed a novel construction scheme for SC-LDPC codes tailored for CV-QKD systems.
• Investigated the correlation between syndrome variation patterns (SVP) and frame error rate (FER).
• Developed and implemented a convergence-based early termination (C-ET) scheme that adaptively adjusts decoding iterations based on SVP convergence.

Main Results:

• The proposed SC-LDPC code construction achieved 97% reconciliation efficiency and flexible code length.
• The C-ET scheme demonstrated a 292% improvement in information throughput compared to the original early termination (ET) scheme at 97% reconciliation efficiency.
• The C-ET scheme reduced decoding latency compared to existing syndrome-based early termination methods.

Conclusions:

• The developed SC-LDPC codes and C-ET scheme significantly enhance reconciliation efficiency and overcome post-processing bottlenecks in CV-QKD.
• These advancements are critical for improving the performance and practicality of high-speed CV-QKD systems.
• The findings represent a substantial step towards enabling secure, long-distance quantum communication.