Reference-frame-independent quantum key distribution network with directly-modulated sources
Phys. Rev. A 113, 052422 – Published 11 May, 2026
DOI: https://doi.org/10.1103/szbp-b3ny
Abstract
Quantum key distribution (QKD) provides an information-theoretic secure method for communication, guaranteeing long-term security against future computational advances. However, as the implementation evolves towards multi-user networks, a significant operational challenge arises: actively compensating for the continuous reference frame drifts between distant nodes. Luckily, reference-frame-independent QKD (RFI-QKD) can circumvent this requirement, offering a practical pathway to scalable quantum communication. Here, we demonstrate a three-node RFI-QKD network built around a central, frequency-configurable, directly-modulated source. The long-term stability of the RFI QKD system is confirmed over a 53 km installed metropolitan fiber link, achieving 24 hours of continuous, recalibration-free operation at a 625 MHz repetition rate. We further show its network reconfigurability by demonstrating on-demand switching between the 52 km user and a second user on a 100 km link, applying user-specific repetition rates to highlight the source's flexibility in a multi-user environment. Our results establish the synergy between the RFI protocol and cost-effective direct-modulation sources as a robust architecture for building low-maintenance, scalable quantum access networks.
