Cisco, Qunnect claim quantum first with datacentre connectivity | Computer Weekly

Qunnect and Cisco have unveiled what they say is the first entanglement-swapping demonstration of its kind over deployed metro-scale fibre using a commercial quantum networking system.

The demonstration combined Qunnect’s room-temperature quantum hardware with Cisco’s quantum networking software stack. The net result of the project is regarded by the partners as being able to bring practical quantum networks closer to scalable deployment, validating a spoke-and-hub model for scaling quantum networks through commercial datacentres.

The companies see these techniques as being able to underpin future ultra-secure links, quantum-safe architectures, and the ability to connect distributed quantum processors and datacentres.

Qunnect believes that one of the challenges in scaling real-world quantum networks is the practical realisation of protocols to route entanglement between network nodes. To achieve that, it says, requires entanglement “swapping”.

That is, the operation that extends entanglement from two nodes to multiple ones through an intermediate hub. Swapping itself is already established in quantum science, but the tech firms stress that performing it on telecom-compatible infrastructure under real-world constraints has remained rare in the industry. Loss, noise and hardware complexity make it far more challenging outside of controlled laboratory settings.

In addition, current quantum networks can be constrained by a complex physical “tether”, relying on a shared master laser to connect all nodes. By using Qunnect’s independent atomic sources, the experiment looked to remove the need for nodes to be physically “tethered” by shared lasers.

To validate their model, Cisco and Qunnect conducted a demonstration on the latter’s GothamQ testbed, which runs throughout New York City in a network that spans 17.6km of deployed telecom fibre connecting Brooklyn and Manhattan through QTD Systems’ datacentre at 60 Hudson Street.

At the centre of this integration is Qunnect’s turnkey Carina system, a technology capable of generating an entangled photon pair. To maintain signal integrity, Qunnect’s automatic polarisation controllers (APCs) continuously compensate for polarisation drift – a persistent challenge in deployed fibre that has historically limited real-world networking.

These technologies were integrated with Cisco’s unified quantum networking software stack, functioning as a “digital air traffic controller” for the city-wide network. The software autonomously coordinates Qunnect’s turnkey Carina hardware across geographically separated nodes.

The collaboration is said to have generated record swapping rates of over 1.7 million pairs/hour locally and 5,400 pairs/hour over deployed fibre. This is said to be nearly 10,000 times better than previous benchmarks using similar platforms. As the first demonstration of polarisation entanglement swapping over deployed fibre, the system maintained over 99% polarisation fidelity.

End nodes used room-temperature detectors, concentrating cryogenic equipment solely at the central hub to significantly reduce the cost of network scaling. Using independent entanglement sources meant no shared lasers, allowing for modular network expansion.

Cisco and Qunnect regard the results from the trial as demonstrating the integrated system can operate reliably in one of the world’s most demanding urban environments, providing a deployable blueprint for distributed quantum computing and secure metro-scale quantum networks.

This decoupling of nodes allowed for a scalable hub-and-spoke architecture for quantum networking, enabling new endpoint nodes to be added without dedicated synchronisation links to all other nodes. The two firms say this achievement serves as a first proof point in a journey towards practical, entanglement-based quantum networks, laying the foundation for distributed quantum computing.

“Entanglement swapping is a fundamental operation in the quantum internet,” said Mehdi Namazi, co-founder and chief science officer for Qunnect. “Today, we not only broke the record for rate and scalability, we did so in New York City using some of the noisiest, most chaotic fibre on earth. This is a milestone the field has been waiting for.”

Reza Nejabati, head of quantum research at Cisco, added: “This milestone accelerates our quantum networking vision. Our orchestration software enabled field-ready entanglement distribution and swapping – foundational capabilities for distributed quantum computing and the global quantum grid.”