Cisco and Qunnect Demonstrate Entanglement Networking Across 17.6 km of Live New York Fiber

February 18, 2026 — Cisco and Qunnect today announced the successful demonstration of quantum entanglement swapping across 17.6 kilometers of standard telecom fiber running beneath New York City. The demonstration achieved entanglement swapping rates roughly 10,000 times better than previous benchmarks using similar platforms: 1.7 million entangled pairs per hour in local operations and 5,400 pairs per hour over the full deployed distance, while maintaining polarization fidelity above 99%.

The demonstration was conducted on Qunnect’s GothamQ testbed, connecting two nodes at Qunnect’s facility in the Brooklyn Navy Yard with a central hub at QTD Systems’ data center at 60 Hudson Street in Manhattan. The scientific results have been published on ArXiv (Craddock et al., 2026).

The bottom line: This is the first demonstration of polarization entanglement swapping over deployed metro-scale fiber, and it achieved rates that move quantum networking from proof-of-concept territory toward something approaching operational viability. For anyone tracking the path to distributed quantum computing, the fact that it worked on live infrastructure — not lab fiber — changes the deployment calculus.

Unlike traditional quantum networking experiments that require shared laser sources between nodes, this architecture separated the quantum hardware layer from the software control plane. Qunnect’s Carina system provided room-temperature entanglement sources at edge nodes with independent atomic sources — no shared master laser connecting the nodes. Cisco’s quantum networking software stack handled orchestration: entanglement distribution, measurement coordination, and picosecond-level timing synchronization across the geographically separated nodes using the White Rabbit timing protocol.

The hub-and-spoke topology concentrated expensive cryogenic equipment (superconducting nanowire single-photon detectors) at the central 60 Hudson Street hub, while the Brooklyn edge nodes used room-temperature single-photon avalanche diode (SPAD) detectors. This architecture reduces the cost of network expansion: adding a new endpoint requires only room-temperature hardware, not another cryogenic installation.

My Analysis

I’ve been tracking quantum networking demonstrations for years, and most stay trapped behind lab doors. This one feels different because it tackled the unglamorous but essential challenge: making quantum states survive the chaos of real urban infrastructure.

Why This Matters More Than the Numbers Suggest

The performance numbers grab attention first. Previous entanglement swapping demonstrations on deployed fiber struggled with rates orders of magnitude lower. But the more significant achievement is what the team didn’t need: pristine dedicated fiber, temperature-controlled environments at every node, or shared physical laser sources between endpoints. Each of those non-requirements represents years of engineering work to eliminate a scaling bottleneck.

The shared laser problem has been a fundamental constraint on quantum networking since its inception. Traditional approaches synchronize quantum states by having nodes literally share the same laser source. That works for two or three nodes in a lab. It becomes physically impossible at network scale. Qunnect’s independent atomic entanglement sources, coordinated by Cisco’s software rather than shared hardware, break this dependency. This shift from hardware-enforced to software-managed synchronization is what transforms quantum networking from a laboratory curiosity into potentially scalable infrastructure.

The 60 Hudson Street Test

Running quantum signals through 60 Hudson Street tells us something specific. This is one of the most densely packed telecommunications facilities in North America, where hundreds of carriers interconnect their networks. The electromagnetic noise, vibrations, and temperature fluctuations in that building represent a worst-case environment for quantum states. If entangled photons can survive passage through 60 Hudson, they can likely survive deployment in any commercial data center.

The analogy to the early internet is apt. The internet grew from ARPANET by proving it could work on existing telephone infrastructure. Quantum networking may follow a similar path, running on the dark fiber already buried beneath cities rather than requiring greenfield quantum-specific infrastructure. This demonstration, along with Cisco’s room-temperature entanglement chip and Universal Quantum Switch (use actual slug), reinforces that thesis.

Connecting to the Quantum Switch

An important detail that emerged after the initial announcement: Cisco’s blog post on the Universal Quantum Switch confirmed that the NYC fiber network was also used to test the switch’s entanglement swapping capabilities. This means the 17.6 km GothamQ testbed is serving as a real-world validation platform for Cisco’s entire quantum networking stack — from entanglement generation (the chip) through software orchestration (the compiler) to routing and switching (the Universal Quantum Switch). Each component is being tested not just in the lab but on live metropolitan fiber.

Reality Check

Before we get carried away: three nodes across 17.6 kilometers is not a quantum internet. Entanglement swapping at 5,400 pairs per hour is impressive relative to previous attempts, but orders of magnitude below what distributed quantum computing or large-scale quantum key distribution will demand. Current fiber carries terabits of classical data per second. Even 1.7 million quantum pairs per hour is a trickle by comparison.

The demonstration also doesn’t address several hard problems that remain open: quantum error correction across the network, routing around node failures, performance degradation with distance and additional nodes, and the integration of quantum repeaters for extending range beyond metropolitan distances. These aren’t oversights in the demonstration — they’re signs of how much work remains.

Strategic Implications

For organizations tracking quantum technology, this demonstration shifts quantum networking from “monitor casually” to “understand deeply” status. Not because deployment is imminent, but because the technical barriers that seemed insurmountable five years ago keep falling.

Consider the security implications. The quantum states coexisted with classical telecommunications traffic on the same fiber. That validates the premise that quantum networking can overlay existing infrastructure rather than requiring dedicated networks — a major economic and practical consideration for any future deployment of quantum key distribution or quantum-secured communications.

The timing matters too. This demonstration came just months after the IBM-Cisco announcement on networked fault-tolerant quantum computing, and just weeks before Cisco unveiled its Universal Quantum Switch. Cisco is systematically validating each layer of its quantum networking stack in real-world conditions. They’re not just publishing papers. They’re running fiber through Manhattan.

What the Engineering Story Tells Us

What impresses me most is the methodical engineering required to make this work. Synchronizing photon arrival times to picosecond precision across kilometers of fiber, through temperature variations and mechanical vibrations, while maintaining quantum coherence is not breakthrough physics. It’s grinding, systematic engineering work — the kind that turns laboratory demonstrations into deployable infrastructure.

The software-hardware separation catches my attention specifically. Quantum experiments traditionally tightly couple every component; adjusting one element requires recalibrating the entire system. Cisco’s approach suggests a more modular future where quantum networking components from different vendors interoperate through standardized interfaces. Qunnect provides the entanglement sources. Cisco provides the orchestration. QTD Systems provides the data center. That’s how classical networking achieved scale, and it’s the model that gives me the most confidence in quantum networking’s eventual deployment.

Implications for CRQC Timelines

This demonstration doesn’t directly change Q-Day predictions. A cryptographically relevant quantum computer requires capabilities across all the dimensions I track in my CRQC Quantum Capability Framework, and networking is just one piece of the puzzle.

But it does make the distributed path to CRQC more concrete. If you can network quantum processors at metropolitan scale with this level of performance, the step to data-center-scale distributed quantum computing becomes an engineering problem rather than a physics problem. As I’ve argued repeatedly, the deadlines for PQC migration are already set by regulators, insurers, and standards bodies. Demonstrations like this add data points suggesting the hardware trajectory toward useful quantum systems — including potentially cryptanalytically relevant ones — remains on track.

What Happens Next

Watch for the node count to expand from three to five, then ten. Watch for distance to stretch from metropolitan to regional. Watch for error rates to improve and throughput to increase. Each increment will reveal new challenges.

More immediately, watch for standardization efforts. As multiple vendors demonstrate quantum networking capabilities (Cisco with Qunnect, IonQ with its photonic interconnects, various university consortia), pressure will build for interoperability standards. The DARPA HARQ program, launched in April 2026 with 19 teams working on heterogeneous quantum interconnects, will accelerate this.

The investment landscape will shift too. Quantum networking has lived in quantum computing’s shadow, receiving a fraction of the funding. Demonstrations that prove the technology works on live infrastructure make near-term applications — distributed quantum computing, quantum-secured communications, synchronized timing networks — tangible enough to attract capital.

Cisco’s Manhattan demonstration marks quantum networking’s transition from laboratory novelty to urban prototype. The timeline remains long — I’d estimate a decade or more before production deployment at scale. But the path grows clearer with each demonstration. As we approach Q-Day for cryptography, we’re simultaneously building the quantum networking infrastructure that will define how quantum computers are accessed, connected, and ultimately secured. Cisco just proved that infrastructure can be built on the fiber already beneath our feet.