Telecommunications-Band Quantum Local Area Networks Support Heterogeneous Quantum Networking Research

The pursuit of secure communication and enhanced sensing drives rapid advances in quantum networking, and researchers are now building practical quantum networks to test these technologies. Erin Sheridan, Nicholas J. Barton, Richard Birrittella, and colleagues at the U. S. Air Force Research Laboratory and collaborating institutions have developed and deployed Quantum Local Area Networks (QLANs) operating at telecommunications wavelengths. These multi-node networks, incorporating both optical fiber and free-space links, connect controlled laboratory settings with challenging outdoor environments, offering a versatile platform for testing quantum communication protocols. The team demonstrates high-fidelity entanglement distribution across deployed fiber in a wooded area, achieving a violation of the Clauser-Horne-Shimony-Holt inequality that nears theoretical limits, and these results highlight the growing feasibility of robust, field-deployable quantum infrastructure capable of connecting diverse quantum systems.

Validating Performance in Emerging Quantum Networks

These deployments require robust methods for characterising and validating quantum network performance, ensuring the reliable operation of emerging quantum systems. The QLANs are designed to be compatible with a variety of quantum technologies, paving the way for heterogeneous networks that can connect different types of quantum systems. The team characterised the performance of these networks by distributing entangled photons across the deployed fibre, even in challenging outdoor environments like wooded areas.

Measurements confirm a high quality of entanglement, with a violation of a key quantum inequality reaching 2.700, very close to the theoretical maximum of 2.828. This result highlights the networks’ ability to maintain delicate quantum states over significant distances, a crucial requirement for future quantum applications. These networks, utilising both optical fibre and free-space links, demonstrate the practical viability of field-deployable quantum network infrastructure capable of operating in diverse conditions. The comprehensive data gathered from these multi-purpose testbeds, including environmental monitoring and signal quality assessments, will be valuable for designing stabilisation solutions, informing quantum network simulations, and improving the prediction of network behaviour. Future work will focus on expanding QLAN functionality to connect different types of matter-based quantum systems, such as superconducting qubits and trapped ions, to achieve interoperability. This research represents a significant step towards building robust and versatile quantum networks capable of supporting a range of applications, from distributed quantum computing to secure communications.