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Multi-node quantum key distribution network using existing underground optical fibre infrastructure

Mariella Minder, Andreas Siakolas, Stephanos Yerolatsitis, Konstantinos Katzis, Kyriacos Kalli

TL;DR

The paper tackles the challenge of securing communications against quantum-enabled attacks by showing that quantum key distribution can be deployed over existing underground optical fibre. It presents a four-node, ring-shaped QKD network in Nicosia that uses bidirectional transmission and wavelength multiplexing to minimize dark fibre usage while maintaining performance. The authors integrate a full stack—quantum layer, key management service, and application-layer encryption—and demonstrate stable key generation with an average SKR of about 2.4 kbps across links, in agreement with theoretical models, and without measurable leakage from live traffic. This work demonstrates the practicality of leveraging existing telecom infrastructure for quantum-secured networks, supporting scalable, cost-effective deployment for critical infrastructure security and paving the way for broader adoption of quantum networks.

Abstract

Quantum key distribution (QKD) offers unconditional information security by allowing two distant users to establish a common encryption key resilient to hacking. Resultingly, QKD networks interconnecting critical infrastructure and enabling the secure exchange of classified information, can provide a solution to the increasing number of successful cyberattacks. To efficiently deploy quantum networks, the technology must be integrated over existing communication infrastructure, such as optical fibre links. Yet, QKD poses stringent requirements on the conditions of the network over which it is deployed. This work demonstrates the first quantum communication network in Cyprus via the deployment of a multi-node quantum network, exploiting existing commercial underground optical fibre. The network employs bidirectional occupation of fibres and wavelength multiplexing in a ring architecture to achieve, with minimal use of dark fibres, high-rate QKD. Results obtained reveal consistent key generation rates across all nodes, confirming reliable operation in a real-world environment. This deployment highlights the feasibility of leveraging existing telecom infrastructure for quantum-secured communication, marking a significant step toward scalable and cost-effective quantum networks suited for critical applications.

Multi-node quantum key distribution network using existing underground optical fibre infrastructure

TL;DR

The paper tackles the challenge of securing communications against quantum-enabled attacks by showing that quantum key distribution can be deployed over existing underground optical fibre. It presents a four-node, ring-shaped QKD network in Nicosia that uses bidirectional transmission and wavelength multiplexing to minimize dark fibre usage while maintaining performance. The authors integrate a full stack—quantum layer, key management service, and application-layer encryption—and demonstrate stable key generation with an average SKR of about 2.4 kbps across links, in agreement with theoretical models, and without measurable leakage from live traffic. This work demonstrates the practicality of leveraging existing telecom infrastructure for quantum-secured networks, supporting scalable, cost-effective deployment for critical infrastructure security and paving the way for broader adoption of quantum networks.

Abstract

Quantum key distribution (QKD) offers unconditional information security by allowing two distant users to establish a common encryption key resilient to hacking. Resultingly, QKD networks interconnecting critical infrastructure and enabling the secure exchange of classified information, can provide a solution to the increasing number of successful cyberattacks. To efficiently deploy quantum networks, the technology must be integrated over existing communication infrastructure, such as optical fibre links. Yet, QKD poses stringent requirements on the conditions of the network over which it is deployed. This work demonstrates the first quantum communication network in Cyprus via the deployment of a multi-node quantum network, exploiting existing commercial underground optical fibre. The network employs bidirectional occupation of fibres and wavelength multiplexing in a ring architecture to achieve, with minimal use of dark fibres, high-rate QKD. Results obtained reveal consistent key generation rates across all nodes, confirming reliable operation in a real-world environment. This deployment highlights the feasibility of leveraging existing telecom infrastructure for quantum-secured communication, marking a significant step toward scalable and cost-effective quantum networks suited for critical applications.

Paper Structure

This paper contains 4 sections, 3 figures.

Table of Contents

  1. Introduction
  2. Network details
  3. Results
  4. Conclusion

Figures (3)

  • Figure 1: a. Map of the four-node (N1-N4) quantum network in Nicosia. The available fibre infrastructure interconnects the nodes via optical distribution frames (ODFs). Each link segment (green line) consists of two dark fibres which vary in length. b. Architecture of the quantum channels. A single fibre per segment carries all quantum signals. Circulators at the nodes direct the light from the transmitters, AN, to the channel and then to the receivers, BN. A circulator at an ODF directs the signals from N4-N1.
  • Figure 2: a. End-user setup: Each node includes two QKD devices, a KMS unit, and a layer 1 encryptor (L1 ENC). Classical signals are multiplexed via DWDM and sent over one fibre; quantum signals use a separate fibre. b. ODF 3 design: Encryption and clock signals follow a ring topology using DWDMs and a circulator, while the KMS layer maintains mesh connectivity.
  • Figure 3: a. Secret key rates acquired over all links for the duration of 5 days. b. Average secret key rate (circles) and QBER (diamonds) per link compared with the theoretically expected lines (SKR sim, QBER sim).