Continuous-variable quantum passive optical network for multi-user quantum key distribution

Quantum key distribution (QKD) is the quantum technology aimed at distributing secret keys with the provable security, based on the principles of quantum physics. After having been implemented in the point-to-point scenarios between two trusted parties, QKD shall be extended to multi-user networks to increase its efficiency and scalability. The existing solutions for quantum networking rely on probabilistic or time-sharing strategies. We propose continuous-variable quantum passive-optical-network (CV-QPON) based on quadrature modulation, passive optical network and homodyne detection of coherent states, enabling deterministic and simultaneous secret key generation among all network users. We demonstrate key generation between 8 users, each with an 11 km span of access link. Depending on the trust assumptions about users, we report up to 2.1 Mbits/s of total network key generation. The proposed CV-QPON protocols offer a pathway toward low-cost, high-rate, and scalable quantum access networks using standard telecom techniques.