Cisco Systems and Brooklyn-based startup Qunnect have completed a metro-scale quantum networking trial across New York City, transmitting entangled photons over nearly 18 kilometers of existing fiber linking Brooklyn and Manhattan. The companies say the demonstration shows that quantum networking can function reliably outside laboratory conditions, using commercial telecom equipment suited for deployment in real-world data centers.
The test ran over Qunnect’s GothamQ network, which spans 17.6 kilometers of deployed fiber and passes through a major data center at 60 Hudson Street. By combining Qunnect’s quantum hardware with Cisco’s orchestration software, the partners achieved high-rate entanglement swapping, a key process needs to extend quantum links across multiple nodes.
In local testing, the system generated roughly 1.7 million entangled photon pairs per hour. Across the full metropolitan fiber route, it sustained several thousand entangled pairs per hour, while maintaining polarization fidelity (which measures how well a system preserves the polarization state of light) above 99%.
According to the companies, those rates significantly exceed previous results using comparable independent-source systems on deployed fiber.
Hurdles and Obstacles Remain
Entanglement swapping enables two distant nodes to share a quantum state even if they have never interacted directly. That capability is considered foundational for a future quantum internet, in which geographically separated quantum processors could exchange information with new levels of security.
Environmental instability remains a hurdle for quantum networking. Fiber in dense cities is subject to temperature changes, vibration and complex routing through patch panels and switching equipment. Qunnect addressed this challenge with automated polarization control technology designed to continuously compensate for drift in the fiber, preserving the fragile quantum states as they travel through the local network.
Cryogenic cooling was another obstacle the companies dealt with. Many quantum systems require extremely low temperatures, which adds cost and complexity to real world use cases. For the New York City trial, cryogenic hardware was centralized at a hub location, while endpoint nodes operated with room-temperature detectors. That design reduces infrastructure demands at the network edge and supports a more scalable model for citywide deployment.
The trial also moved away from the traditional approach of linking quantum nodes through a shared master laser. Instead, Qunnect used independent atomic entanglement sources, allowing nodes to operate without being physically tethered to a common laser reference. This decoupling supports a hub-based set up in which additional nodes can be added without extensive reconfiguration.
Cisco’s Support
Cisco contributed a unified software stack that coordinated the entanglement sources and managed synchronization across the network. The company views orchestration as essential to scaling quantum systems beyond small research setups. By automating configuration and control, Cisco aims to apply lessons from traditional networking to quantum infrastructure.
The project is an early but important step toward linking multiple quantum processors within a data center and eventually connecting separate quantum data centers. The longer-term goal is to enable distributed quantum computing, where tasks could be shared among specialized quantum machines.
In the nearer term, quantum networking could support applications that demand ultra-low latency coordination. Financial trading systems, for example, might benefit from entanglement-based techniques that reduce timing constraints between geographically separated computing systems.
Integrating these networking capabilities with operational quantum computers, across multiple hardware environments, is the next major challenge. Cisco has signaled interest in ensuring its networking approach can interface with a range of quantum technologies, from superconducting qubits to photonic systems. As a good first step, the New York demonstration provides evidence that quantum networking can move beyond controlled laboratory conditions.
