High-precision time synchronization for remote clocks plays an important role in fundamental science^1,2,3 and real-life applications^4,5. However, current time synchronization techniques^6,7 have been shown to be vulnerable to sophisticated adversaries⁸. There is a compelling need for fundamentally new methods to distribute high-precision time information securely. Here, we propose a satellite-based quantum-secure time transfer (QSTT) scheme based on two-way quantum key distribution in free space and experimentally verify the key technologies of the scheme via the Micius quantum satellite. In QSTT, a quantum signal (for example, a single photon) is used as the carrier for both the time transfer and the secret-key generation, offering quantum-enhanced security for transferring the time signal and time information. We perform a satellite-to-ground time synchronization using single-photon-level signals and achieve a quantum bit error rate of less than 1%, a time data rate of 9 kHz and a time-transfer precision of 30 ps. These results offer possibilities towards an enhanced infrastructure for a time-transfer network, whose security stems from quantum physics.

远程时钟的高精度时间同步在基础科学^1,2,3和实际应用^4,5中起着重要作用。但是，目前的时间同步技术^6,7已显示出容易受到复杂对手的攻击⁸。迫切需要一种基本的新方法来安全地分发高精度时间信息。在此，我们提出了一种基于自由空间中双向量子密钥分配的基于卫星的量子安全时间转移（QSTT）方案，并通过Micius量子卫星通过实验验证了该方案的关键技术。在QSTT中，量子信号（例如，单个光子）被用作时间传输和密钥生成的载体，从而为传输时间信号和时间信息提供了量子增强的安全性。我们使用单光子级信号执行卫星到地面的时间同步，并实现小于1％的量子误码率，9 kHz的时间数据率和30 ps的时间传递精度。