Jonas Treplin

Advantage Distillation (AD) is a classical post-processing technique that enhances Quantum Key Distribution (QKD) protocols by increasing the maximum acceptable Quantum Bit Error Rate (QBER) and thus extending the distance at which QKD links can be securely established. AD operates by post-selecting blocks of bits and extracting fewer high-fidelity bits, exhibiting a reduced QBER and thus lowering the amount of information that has to be disclosed during the information reconciliation step. In this work we present the first comprehensive finite key-size analysis of decoy-state BB84 enhanced via AD post-processing. We demonstrate that through the use of AD the maximum acceptable QBER increases from around 9.5% to around 17.3% for realistic key sizes. This result shows that substantial performance enhancements can be achieved in scenarios which are constrained by the maximum tolerable QBER via improvements of the post-processing method alone.

Quantum Key Distribution (QKD) can be performed securely only when the Quantum Bit Error Rate (QBER) is below a certain threshold which, due to the unavoidable presence of noise, limits the maximum transmission distance. Advantage Distillation (AD) is a classical post-processing technique that enhances QKD protocols by increasing error tolerance, thus extending the communication range. AD operates by post-selecting blocks of bits and extracting fewer correlated bits between Alice and Bob, which exhibits a reduced QBER, while Eve's mutual information does not significantly increase. This process ultimately lowers the information disclosure in the information reconciliation step, while the relative key shortening during privacy amplification remains largely unaffected. In this study, we present the first comprehensive finite key size analysis of the decoy-state version of the BB84 protocol including AD post-processing. Our results demonstrate a notable improvement in QBER tolerance through AD, with the 1-decoy version outperforming the 2-decoy version of the protocol. This analysis has significant implications for long-distance and satellite-based QKD applications, which are constrained by QBER, as it shows that substantial performance enhancements can be achieved by improved post-processing techniques.