Measurement-device-independent quantum key distribution (MDI-QKD) closes all the security loopholes in the detection system and is a promising solution for secret key sharing. Polarization encoding is the most common QKD encoding scheme, as it is straightforward to prepare and measure. However, implementing polarization encoding in MDI QKD imposes extra challenges, as polarization alignment must be maintained over both mutually unbiased bases and be maintained for both paths (Alice-Charlie and Bob-Charlie). Polarization alignment is usually done by interrupting the QKD process (reducing overall key generation rates) or using additional classical laser sources multiplexed with quantum channels for polarization alignment. Since low key rates and cost are the two most pressing challenges preventing wide adoption of QKD systems, using additional resources or reducing key rates runs contrary to making QKD commercially viable. Therefore, we propose and implement a novel polarization compensation scheme in the MDI-QKD system that avoids the aforementioned drawbacks by recycling part of discarded detection events. Our scheme evaluates the polarization drift in real-time based on single measurements corresponding to decoy intensities. Our fully automated experimental demonstration maintains the average polarization drift below 0.13 rad over 40 km of spooled fibre (without an insulating jacket) for at least four hours. The average quantum bit error rate is 3.8$\%$, and we achieved an average key rate of $7.45\times 10^{-6}$ bits per pulse.

中文翻译：

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针对带有拒绝数据的 MDI-QKD 的资源高效型实时偏振补偿


独立于测量设备的量子密钥分发（MDI-QKD）弥补了检测系统中的所有安全漏洞，是一种很有前途的密钥共享解决方案。偏振编码是最常见的 QKD 编码方案，因为它易于准备和测量。然而，在 MDI QKD 中实现偏振编码带来了额外的挑战，因为必须在两个相互无偏的基础上保持偏振对齐，并为两条路径（Alice-Charlie 和 Bob-Charlie）保持偏振对齐。偏振对准通常通过中断 QKD 过程（降低总体密钥生成率）或使用与量子通道复用的额外经典激光源进行偏振对准来完成。由于低密钥率和成本是阻碍 QKD 系统广泛采用的两个最紧迫的挑战，因此使用额外资源或降低密钥率与 QKD 商业可行性背道而驰。因此，我们在MDI-QKD系统中提出并实现了一种新颖的偏振补偿方案，通过回收部分丢弃的检测事件来避免上述缺点。我们的方案根据与诱饵强度相对应的单次测量来实时评估偏振漂移。我们的全自动实验演示使 40 公里缠绕光纤（无绝缘护套）的平均偏振漂移保持在 0.13 rad 以下至少四​​个小时。平均量子误码率为 3.8$\%$，我们实现了每脉冲 $7.45\times 10^{-6}$ 位的平均密钥率。