Global Navigation Satellite Systems (GNSSs), such as GPS and Galileo, provide precise time and space coordinates globally and constitute part of the critical infrastructure of modern society. To reliably operate GNSS, a highly accurate and stable system time is required, such as the one provided by several independent clocks hosted in Precise Timing Facilities (PTFs) around the world. The relative clock offset between PTFs is periodically measured to have a fallback system to synchronize the GNSS satellite clocks. The security and integrity of the communication between PTFs is of paramount importance: if compromised, it could lead to disruptions to the GNSS service. Therefore, securing the communication between PTFs is a compelling use-case for protection via Quantum Key Distribution (QKD), since this technology provides information-theoretic security. We have performed a field trial demonstration of such a use-case by sharing encrypted time synchronization information between two PTFs, one located in Oberpfaffenhofen (Germany) and one in Matera (Italy)—more than 900 km apart. To bridge this large distance, a satellite-QKD system is required, plus a “last-mile” terrestrial link to connect the optical ground station (OGS) to the actual location of the PTF. In our demonstration, we have deployed two full QKD systems to protect the last-mile connection at both locations and have shown via simulation that upcoming QKD satellites will be able to distribute keys between Oberpfaffenhofen and Matera, exploiting already existing OGSs.

全球导航卫星系统 (GNSS)，例如 GPS 和伽利略，在全球范围内提供精确的时间和空间坐标，构成现代社会关键基础设施的一部分。为了可靠地运行 GNSS，需要高度准确和稳定的系统时间，例如由世界各地精密授时设施 (PTF) 中托管的多个独立时钟提供的时间。定期测量 PTF 之间的相对时钟偏移，以便有一个后备系统来同步 GNSS 卫星时钟。PTF 之间通信的安全性和完整性至关重要：如果受到损害，可能会导致 GNSS 服务中断。因此，确保 PTF 之间的通信安全是通过量子密钥分发 (QKD) 进行保护的一个引人注目的用例，因为该技术提供了信息论安全性。我们通过在两个 PTF 之间共享加密的时间同步信息，对此类用例进行了现场试验演示，其中一个位于 Oberpfaffenhofen（德国），一个位于马泰拉（意大利），相距 900 多公里。为了弥合如此长的距离，需要卫星 QKD 系统，以及将光学地面站 (OGS) 连接到 PTF 实际位置的“最后一英里”地面链路。在我们的演示中，我们部署了两个完整的 QKD 系统来保护两个地点的最后一英里连接，并通过模拟表明即将推出的 QKD 卫星将能够利用现有的 OGS 在 Oberpfaffenhofen 和马泰拉之间分发密钥。