Reliable hands-off entanglement-based QKD system for fiber networks

Quantum cryptography or more specifically quantum key distribution (QKD) is the most advanced quantum information protocol. We present here an entanglement-based QKD system designed to work at 1550 nm for optimal distribution in optical fibers using the BBM92 protocol. Our QKD system is realised as a compact device. The start-up and alignment is fully automated and stabilisation routines guarantee a hands-off and long-term operation. We show a reliable and stable key generation during a two-week demonstration over a 16km fiber. The results show the maturity reached in two-photon entanglement systems by automatically correcting for environmental changes. The high purity of the shared entangled state makes applications such as QKD possible and hopefully also stimulates the application of other quantum communication protocols in optical fibers.