Field Demonstration of Trusted-Node QKD over Deployed Single-Mode and Multi-Core Fiber Infrastructure

A collaborative research team involving Linköping University, KTH Royal Institute of Technology, Stockholm University, and Chalmers University of Technology has successfully demonstrated a long-haul, trusted-node Quantum Key Distribution (QKD) system integrated into a dynamic telecommunications network. The field trial covered a total distance of 303 km in southeastern Sweden, effectively bridging a laboratory in Linköping with a national quantum hub in Stockholm. The architecture utilized a combination of deployed dark fiber and a multi-core fiber access segment, showcasing the viability of quantum communication over heterogeneous, real-world infrastructure.

To overcome significant signal attenuation, the team modified commercial ThinkQuantum systems, integrating Superconducting Nanowire Single-Photon Detectors (SNSPDs) to achieve high detection efficiency and low dark count rates. This upgrade improved the Secret Key Rate (SKR) performance. The network successfully maintained secure key generation while simultaneously transmitting classical 10 Gbps Ethernet data, with an added layer of optical noise to simulate crosstalk. The experiment operated continuously for 92 hours, utilizing Key Management Systems (KMS) to handle fluctuations in key generation rates between the network spans.

Furthermore, the team validated the system by using the generated keys for One-Time Pad (OTP) encrypted image transmission. Comparing traditional JPEG 2000 compression with deep-learning-based JPEG AI, the researchers demonstrated that under constrained key budgets, the AI-driven codec provided superior perceptual quality and efficient bit allocation. The full study details the hardware configuration, crosstalk modeling, and encryption parameters, providing a roadmap for future quantum-secure communication deployments.

Source: quantumcomputingreport.com
Publication date: 09.06.2026
Author: Mohamed Abdel-Kareem