On the Same Fiber Carrying 400G Data Center Traffic
Researchers at Duke University and the University of Maryland have demonstrated that quantum networking signals can coexist on the same physical fiber as live data center-grade traffic, according to a report from SDxCentral and a corresponding technical paper. The team distributed ion-photon entanglement over a 1.7-mile deployed fiber loop on Duke’s campus while that same fiber simultaneously carried Ethernet traffic at 400 gigabits per second and an analog 5G radio signal.
The experiment matters for networking infrastructure planning because quantum networks have historically required dedicated “dark fiber” — unused optical fiber with no other traffic running through it — to avoid interference between fragile quantum signals and the powerful light pulses used for conventional data transmission. If quantum and classical traffic can reliably share the same strand, it would remove a significant cost and deployment barrier as quantum networking moves from the lab toward real-world use.
How the experiment worked
The researchers used wavelength-division multiplexing — a standard technique in fiber optic networking that sends multiple signals down one fiber on different wavelengths of light — to combine the quantum and classical signals on the same underground loop. A trapped strontium ion was entangled with a photon transmitted at 1,092 nanometers, a wavelength deliberately chosen to sit outside the telecom bands used by the Ethernet and 5G signals, allowing researchers to filter out unwanted light before it reached their single-photon detectors.
Critically, the 400 Gb/s Ethernet channel used coherent optics representative of an actual data center interconnect, while the second classical channel emulated a 5G connection between a central office and a base station — meaning the test conditions closely mirrored the kind of live, mixed traffic found on real telecom and data center fiber routes rather than a sanitized lab setup.
The results
Over nearly 14 hours of continuous operation, the system recorded 32,500 photon detection events, corresponding to an entanglement generation rate of roughly 39.3 events per minute, according to SDxCentral’s reporting on the study. The researchers characterized the result as the first demonstration of memory-based quantum entanglement — the kind needed to eventually link quantum processors, memories and sensors — successfully coexisting with standard telecom traffic on a single fiber, a milestone distinct from earlier experiments that used purely photonic (rather than memory-based) entanglement schemes.
What this means for data center networking
For an industry racing to build out fiber capacity for AI workloads, the implications extend beyond quantum computing research. Hyperscalers are already deploying enormous volumes of new fiber for data center interconnect, and dark fiber availability is a persistent constraint as AI campuses multiply. A demonstrated path for quantum signals to ride alongside production Ethernet and 5G traffic, rather than demanding their own dedicated strands, could meaningfully reduce future infrastructure costs as quantum networking capabilities mature and organisations look to link quantum processors across metro and campus distances, much as today’s data center interconnect links GPU clusters across buildings.
The experiment adds to a broader body of recent work on quantum-classical fiber coexistence, including NIST-led demonstrations earlier this year that successfully distributed entangled photons over tens of kilometres of aerial and commercial fiber. Together, these results suggest the fiber infrastructure being built today for AI-driven data center growth may ultimately do double duty, carrying both classical and quantum traffic on the same glass.
