Towards satellite-based quantum-secure time transfer

Transmitting the time signal and generating the secure key with the same carrier photon improves the security of a satellite-based quantum-secure time transfer protocol, which uses two-way quantum key distribution. High-precision time synchronization for remote clocks plays an important role in fundamental science(1-3) and real-life applications(4,5). However, current time synchronization techniques(6,7) have been shown to be vulnerable to sophisticated adversaries(8). 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.