Due to the single-photon interference at a third untrusted party, the twin-field quantum key distribution (TF-QKD) protocol and its variants can beat the well-known rate-loss bound without quantum repeaters and related experiments have recently been implemented. In general, quantum states in these schemes should be randomly switched between the code mode and the test mode. To adopt the standard decoy-state method, the phases of coherent-state sources in the test mode are assumed to be continuously randomized. However, such a crucial assumption cannot be satisfied well in experimental implementations. In this paper, to bridge the gap between theory and practice, we propose a TF-QKD variant with discrete-phase-randomized sources both in the code mode and the test mode and prove its security against collective attacks. Our simulation results indicate that, with only a small number of discrete phases, the performance of discrete-phase-randomized sources can overcome the rate-loss bound and approach that of continuous-phase-randomized sources.

中文翻译：

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具有离散相随机源的双场量子密钥分配

由于在不受信任的第三方受到单光子干扰，因此双场量子密钥分配（TF-QKD）协议及其变体可以克服众所周知的速率损失范围，而无需量子中继器，并且最近已实施了相关实验。通常，这些方案中的量子态应在编码模式和测试模式之间随机切换。为了采用标准的诱饵态方法，假设测试模式下相干态源的相位是连续随机的。然而，在实验实施中不能很好地满足这样的关键假设。在本文中，为了弥合理论与实践之间的鸿沟，我们提出了一种TF-QKD变体，该变体在代码模式和测试模式下均具有离散相随机源，并证明了其抵抗集体攻击的安全性。