Differential-phase-shift (DPS) quantum key distribution stands as a promising protocol due to its simple implementation, which can be realized with a train of coherent pulses and a passive measurement unit. To implement the DPS protocol, it is crucial to establish security proofs incorporating practical imperfections in users’ devices, however, existing security proofs make unrealistic assumptions on the measurement unit using a Mach–Zehnder interferometer. In this paper, we enhance the implementation security of the DPS protocol by incorporating a major imperfection in the measurement unit. Specifically, our proof enables us to use practical beam splitters with a known range of the transmittance rather than the one with exactly 50%, as was assumed in the existing security proofs. Our numerical simulations demonstrate that even with fluctuations of ±0.5% in the transmittance from the ideal value, the key rate degrades only by a factor of 0.57. This result highlights the feasibility of the DPS protocol with practical measurement setups.

中文翻译：

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带有实用马赫-曾德干涉仪的差分相移 QKD


差分相移（DPS）量子密钥分发由于其简单的实现而成为一种有前途的协议，可以通过一系列相干脉冲和无源测量单元来实现。为了实现DPS协议，建立包含用户设备实际缺陷的安全证明至关重要，然而，现有的安全证明对使用马赫-曾德干涉仪的测量单元做出了不切实际的假设。在本文中，我们通过引入测量单元中的一个主要缺陷来增强DPS协议的实现安全性。具体来说，我们的证明使我们能够使用具有已知透射率范围的实用分束器，而不是像现有安全证明中假设的那样，使用恰好 50% 的分束器。我们的数值模拟表明，即使透射率与理想值相差 ±0.5%，关键速率也仅下降 0.57 倍。这一结果凸显了 DPS 协议在实际测量设置中的可行性。