Quantum-dot-based single-photon sources are key assets for quantum information technology, supplying on-demand scalable quantum resources for computing and communication. However, long-lasting issues such as limited long-term stability and source brightness have traditionally impeded their adoption in real-world applications. Here, we realize a quantum key distribution field trial using true single photons across an 18-km-long dark fibre, located in the Copenhagen metropolitan area, using an optimized, state-of-the-art, quantum-dot single-photon source frequency-converted to the telecom wavelength. A secret key generation rate of > 2 kbits/s realized over a 9.6 dB channel loss is achieved with a polarization-encoded BB84 scheme, showing remarkable stability for more than 24 hours of continuous operation. Our results highlight the maturity of deterministic single-photon source technology while paving the way for advanced single-photon-based communication protocols, including fully device-independent quantum key distribution, towards the goal of a quantum internet.

基于量子点的单光子源是量子信息技术的关键资产，为计算和通信提供按需可扩展的量子资源。然而，长期稳定性和光源亮度有限等长期存在的问题传统上阻碍了它们在实际应用中的采用。在这里，我们使用优化的最先进的量子点单光子源，在位于哥本哈根大都市区的 18 公里长的暗光纤上实现了量子密钥分发现场试验频率转换为电信波长。通过偏振编码 BB84 方案，在 9.6 dB 信道损耗下实现了 > 2 kbits/s 的密钥生成速率，在超过 24 小时的连续运行中表现出卓越的稳定性。我们的结果凸显了确定性单光子源技术的成熟，同时为先进的基于单光子的通信协议（包括完全独立于设备的量子密钥分发）铺平了道路，以实现量子互联网的目标。