Quantum key distribution (QKD) based on entangled photon pairs holds the potential for repeater-based quantum networks connecting clients over long distance. We demonstrate long-distance entanglement distribution by means of polarisation-entangled photon pairs through two successive deployed 96 km-long telecommunications fibres in the same submarine cable. One photon of each pair was detected directly after the source, while the other travelled the fibre cable in both directions for a total distance of 192 km and attenuation of 48 dB. The observed two-photon Bell state exhibited a fidelity 85 ± 2% and was stable over several hours. We employed neither active stabilisation of the quantum state nor chromatic dispersion compensation for the fibre.

基于纠缠光子对的量子密钥分配（QKD）为基于中继器的量子网络连接长距离客户端提供了潜力。我们通过极化纠缠的光子对通过同一条海底光缆中的两个连续部署的96 km长的电信光纤演示了远距离纠缠分布。在光源之后直接检测到每对中的一个光子，而另一对光子在两个方向上沿光缆传输，总距离为192 km，衰减为48 dB。观察到的双光子钟形表现出保真度85±2％，并在数小时内保持稳定。我们既未对光纤进行量子态的主动稳定化也未采用色散补偿。