Twin-field (TF) quantum key distribution (QKD) was conjectured to beat the private capacity of a point-to-point QKD link by using single-photon interference in a central measuring station. This remarkable conjecture has recently triggered an intense research activity to prove its security. Here, we introduce a TF-type QKD protocol which is conceptually simpler than the original proposal. It relies on the pre-selection of a global phase, instead of the post-selection of a global phase, which significantly simplifies its security analysis and is arguably less demanding experimentally. We demonstrate that the secure key rate of our protocol has a square-root improvement over the point-to-point private capacity, as conjectured by the original TF QKD.

通过在中央测量站中使用单光子干扰，推测双场（TF）量子密钥分配（QKD）会击败点对点QKD链路的专用容量。这个惊人的猜想最近引发了激烈的研究活动，以证明其安全性。在这里，我们介绍一种TF型QKD协议，该协议在概念上比原始建议要简单。它依赖于全局阶段的预选择，而不是全局阶段的后选择，这大大简化了其安全性分析并且可以说对实验的要求更低。正如原始TF QKD所推测的那样，我们证明了我们协议的安全密钥速率在点对点私有容量方面具有平方根改进。