Decoy-state quantum key distribution over long-distance optical fiber
Giulia Guarda, Domenico Ribezzo, Daniela Salvoni, Ciro Bruscino, Pasquale Ercolano, Mikkel Ejrnaes, L. Parlato, Cai Zhang, Hao Li, Lixing You, Ilaria Vagniluca, Claudia De Lazzari, Tommaso Occhipinti, Giovanni Piero Pepe, Alessandro Zavatta, Davide Bacco · 2024
Today’s society heavily relies on secure communications, which can be guaranteed by Quantum Key Distribution (QKD), the most mature quantum technology. However, achieving long-distance links without relying on trusted nodes is still challenging. An important limitation is the non-ideality of detection systems, where intrinsic dark counts can hinder key extraction. This work proposes using state-of-the-art superconducting nanowire singlephoton detectors (SNSPD) with ultra-low dark count rates (<1 Hz) to reduce the quantum bit error rate (QBER) and achieve a higher secret key rate. Together with a high-rate QKD transmitter and a self-stabilizing receiver, we enabled a key exchange over 55 dB, corresponding to 340 km over an ultra-low-loss optical fiber.