Twin-field quantum key distribution can overcome the secret key capacity of repeaterless quantum key distribution via single-photon interference. However, to compensate for the channel fluctuations and lock the laser fluctuations, the techniques of phase tracking and phase locking are indispensable in experiment, which drastically increase experimental complexity and hinder free-space realization. We herein present an asynchronous measurement-device-independent quantum key distribution protocol that can surpass the secret key capacity even without phase tracking and phase locking. Leveraging the concept of time multiplexing, asynchronous two-photon Bell-state measurement is realized by postmatching two interference detection events. For a 1 GHz system, the new protocol reaches a transmission distance of 450 km without phase tracking. After further removing phase locking, our protocol is still capable of breaking the capacity at 270 km. Intriguingly, when using the same experimental techniques, our protocol has a higher key rate than the phase-matching-type twin-field protocol. In the presence of imperfect intensity modulation, it also has a significant advantage in terms of the transmission distance over the sending-or-not-sending-type twin-field protocol. With high key rates and accessible technology, our work provides a promising candidate for practical scalable quantum communication networks.

中文翻译：

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用异步双光子干涉打破量子密钥分配的速率损失界限

双场量子密钥分发可以通过单光子干扰克服无中继量子密钥分发的密钥容量。然而，为了补偿通道波动和锁定激光波动，相位跟踪和锁相技术在实验中是必不可少的，这大大增加了实验的复杂性，阻碍了自由空间的实现。我们在此提出了一种独立于异步测量设备的量子密钥分发协议，即使没有相位跟踪和锁相，它也可以超过密钥容量。利用时间复用的概念，异步双光子贝尔态测量是通过后匹配两个干扰检测事件来实现的。对于 1 GHz 系统，新协议无需相位跟踪即可达到 450 km 的传输距离。在进一步去除锁相后，我们的协议仍然能够在 270 公里处突破容量。有趣的是，当使用相同的实验技术时，我们的协议比相位匹配型双场协议具有更高的密钥速率。在存在不完善的强度调制的情况下，它在传输距离方面也比发送或不发送型双场协议具有显着优势。凭借高密钥速率和可访问的技术，我们的工作为实用的可扩展量子通信网络提供了一个有希望的候选者。它在传输距离方面也比发送或不发送型双场协议具有显着优势。凭借高密钥速率和可访问的技术，我们的工作为实用的可扩展量子通信网络提供了一个有希望的候选者。它在传输距离方面也比发送或不发送型双场协议具有显着优势。凭借高密钥速率和可访问的技术，我们的工作为实用的可扩展量子通信网络提供了一个有希望的候选者。