The greatest networking challenges are not solved in pristine labs—they are solved in the real, messy world. Actual operating conditions, with all their noise and unpredictability, are the ultimate test for any new technology aiming for practical use.  

Recently, we took a monumental step in proving the viability of quantum networking by moving it out of the controlled environment and onto standard fiber that runs alongside other telecom traffic  beneath the streets of Manhattan, Brooklyn, and the Hudson River, including traversing the historic and storied carrier hotel at 60 Hudson.   

Just as Cisco helped build the networking fabric for the classical internet, we have been building the foundation for the quantum era through our Cisco Quantum Labs, our quantum network entanglement chip, and the quantum networking software stack we’ve developed over the past several years.  

This experiment is the latest milestone in that journey, and it proved that our approach works with real fiber, in a live metropolitan environment , on infrastructure that already exists, bringing us closer to use cases such as distributed quantum computing, quantum-secured communication, globally synchronized databases with perfectly synced clocks, and networks where eavesdropping is detectable by physics..  

For enterprises, this matters because quantum networking is moving from fragile laboratory work to infrastructure that can be deployed and scaled on the same fiber already running their networks today. 

In a landmark collaboration with our partners Qunnect, New York University, and QTD Systems, we executed an industry-first demonstration. We validated an entanglement-based quantum network across 17.6 kilometers of standard telecom fiber, connecting three nodes between Brooklyn and Manhattan. This successful test validates a core part of Cisco’s strategy: building the practical, horizontally distributed foundation for a scalable quantum internet. 

A breakthrough in real-world scalability 

The results were transformative, and they demonstrated that this technology is ready to move beyond the lab. We achieved entanglement swapping rates (the equivalent of packet operations) of over 5,400 pairs per hour deployed, and 1.7 million pairs per hour locally – figures that are roughly 3 and 4 orders of magnitude better than previous attempts even in lab environments. The system maintained a polarization fidelity above 99%, confirming the high quality and stability of the quantum connection even amidst the noise of a dense urban environment. These are the kind of performance benchmarks that move quantum networking from research milestone toward commercially viable infrastructure. 

The numbers are impressive. The environment is real. But the results were significant for another breakthrough—we broke the physical tether that has limited the scale of quantum experiments for years. 

Traditional quantum networking research often relies on a shared laser to physically link and synchronize nodes. This approach is effective for a handful of nodes in a lab but is fundamentally unscalable. It is like requiring every computer on the internet to be connected to the same power cord. A global quantum internet cannot be built on an architecture that demands every new node be hardwired to its neighbor’s laser. Our results proved there is a better way, paving the way for distributed quantum infrastructure. 

The architecture of success: control and hardware separation 

To validate this first step towards an interoperable distributed quantum internet, we used well-understood software-hardware separation design patterns of software defined networking by deploying hardware from Qunnect and protocol and control plane software from Cisco.  

The Cisco protocol, control and orchestration layer automated the complex entanglement distribution  and measurement coordination across the three geographically separate nodes.  It captured the measurement of millions of photon detection events, synchronizing everything with picosecond-level accuracy using the White Rabbit timing protocol.  

When photons from independent sources miles apart are traveling toward a central hub, they must arrive within a window of a few hundred picoseconds. If the timing is off by even a fraction of a nanosecond, the quantum handshake fails and the connection is lost. Our software ensured this delicate timing was maintained flawlessly. 

Furthermore, the software automated the complex calibration workflows that would otherwise require teams of physicists to travel between nodes for manual adjustments—a process that is not only time-consuming but impossible to scale. 

A blueprint for the Quantum Internet 

This demonstration validates a hub-and-spoke architecture that is both scalable and practical. By placing specialized, cryogenic equipment at central hub and deploying cost-effective, room-temperature hardware at the network edges, we can dramatically reduce the cost and complexity of expansion. New nodes can be added without rebuilding the core synchronization infrastructure. 

The successful use of existing telecom fiber is another critical takeaway. It shows that we can build the quantum internet on the fiber infrastructure we already have, accelerating deployment and reducing barriers to adoption.  

Qunnect’s hardware generated the raw entanglement while Cisco’s software that made it possible to sustain and scale that performance in a dynamic, real-world setting. Together they showed that this internet can be built in an interoperable manner, with best-in-class compontents from different vendors working in a unified system.  

For a deeper technical dive into the methodology, architecture, and full results, check out the blog from our research team at Cisco Quantum Labs and ArXiv research paper.  

In the interest of full transparency, Cisco is an investor in Qunnect.