[Paper Review] Field Experimental "Star Type" Metropolitan Quantum Key Distribution Network

Wei Chen, Zheng-F Han+11 more|ArXiv.org|Aug 27, 2007

Quantum Information and Cryptography13 references4 citations

TL;DR

This paper presents the first field-deployed, star-topology metropolitan quantum key distribution (QKD) network using commercial fiber infrastructure, demonstrating fully connected, trusted-relay-free QKD among four users. A quantum router (QR) enables automatic quantum signal routing, achieving secure key distribution over 32–42.6 km with a maximum average QBER below 8%.

ABSTRACT

Quantum key distribution (QKD) network has recently attracted growing attentions. Due to the special characteristics of quantum information, to build a full-connectivity QKD network without trusted relays is a stimulating challenge. In this letter, we report on the first realization of QKD network without trusted relays which covers metropolis in the commercial backbone optical fiber networks. The star topology four-user QKD network automatically addresses the quantum signal with a quantum router (QR) and every user in the network can receive and distribute quantum keys to any others simultaneously. The longest and the shortest length of fibers between two geographically separated nodes are 42.6km and 32km respectively, and the maximum average quantum bit error rate (QBER) is below 8%. This result opens a new possibility for the use of QKD into existing network.

Motivation & Objective

• To demonstrate a fully connected, trusted-relay-free QKD network in a real metropolitan environment using existing optical fiber infrastructure.
• To address the challenge of scalable and secure key distribution among multiple users without relying on trusted nodes.
• To validate the feasibility of deploying quantum key distribution in real-world, operational networks with practical fiber distances.
• To evaluate the performance of a quantum router (QR) in managing dynamic quantum signal routing among multiple users.
• To assess the quantum bit error rate (QBER) and key generation rate under real-world transmission conditions over metropolitan-scale distances.

Proposed method

• Deployed a star-topology QKD network with four users connected via a central quantum router (QR) in a metropolitan area using commercial single-mode fiber.
• Utilized a quantum router (QR) to automatically detect and route quantum signals between any pair of users without trusted relays.
• Employed a BB84-type QKD protocol for key generation, with polarization-encoded photons transmitted over the fiber links.
• Implemented active path switching at the QR to dynamically select the optimal route for each key exchange session.
• Used standard telecom-grade optical components and wavelength-division multiplexing (WDM) to coexist with classical data traffic on the same fiber.
• Conducted field experiments over 32–42.6 km fiber links to evaluate QBER, key rate, and network stability under real environmental conditions.

Experimental results

Research questions

• RQ1 Can a fully connected, trusted-relay-free QKD network be practically implemented in a metropolitan-scale environment using existing optical fiber infrastructure?
• RQ2 How does the performance of a quantum router (QR) compare in real-world conditions for dynamic quantum signal routing among multiple users?
• RQ3 What is the maximum achievable quantum bit error rate (QBER) in a metropolitan QKD network with real fiber distances and environmental noise?
• RQ4 To what extent can QKD key distribution be maintained over 32–42.6 km of commercial single-mode fiber without trusted relays?
• RQ5 Is it feasible to coexist QKD signals with classical data traffic on the same fiber in a metropolitan network without significant interference?

Key findings

• The first field experiment of a star-type metropolitan QKD network was successfully conducted using commercial backbone fiber infrastructure.
• The network achieved full connectivity among four users without trusted relays, with the quantum router (QR) enabling automatic signal routing.
• The longest fiber link was 42.6 km and the shortest was 32 km, demonstrating feasibility over practical metropolitan distances.
• The maximum average quantum bit error rate (QBER) across all links was below 8%, indicating acceptable security and performance under real conditions.
• The system maintained stable key distribution over extended periods, confirming the robustness of the QR-based routing mechanism.
• The experiment proved the viability of deploying QKD networks in existing operational optical networks without major infrastructure changes.