NIST, the University of Maryland, and Qunnect published results on August 6, 2026, describing a 62-kilometer entanglement distribution experiment run over live commercial telecommunications fiber connecting NIST's Gaithersburg campus to UMD's College Park campus. The result that separates this from a typical lab demonstration is durability, not distance: the setup sustained a Bell inequality violation for more than 20 consecutive hours during a 24-hour continuous stress test, on fiber that was partially aerial and exposed to wind, traffic vibration, and temperature swings the whole time.
Why aerial commercial fiber is the harder problem
Most published entanglement distribution records come from dedicated, environmentally shielded fiber, often buried and purpose-built for the experiment. That is not what most real metropolitan networks look like. Commercial fiber includes aerial spans strung on poles, subject to wind sway and thermal expansion, both of which scramble the polarization state that carries the quantum information. A photon that survives 62 km of buried, temperature-stable fiber is a different achievement than one that survives 62 km of fiber swinging in the wind next to a road. This experiment ran on the second, harder kind.
The engineering that made it hold up
The team generated entangled signal and idler photon pairs at NIST Gaithersburg, sending the idler photon to a receiver and time-tagging unit at UMD while keeping a polarization analyzer for the signal photon at the source, with a parallel optical link for timing synchronization. The part responsible for the 20-hour stability is Qunnect's automated polarization compensation (APC) hardware, which multiplexes a reference light beam through the same fiber to continuously measure polarization drift and apply a correcting inverse transformation in real time. Without that active correction, aerial fiber's constant polarization drift would degrade entanglement fidelity well before 20 hours.
The numbers
The system distributed entangled photon pairs at approximately 1,500 pairs per second, with 92.8% operational uptime, meaning only 7.2% of the run went to active recalibration rather than photon transmission. The CHSH Bell inequality parameter measured S = 2.45 ± 0.08, comfortably above the classical threshold of S ≤ 2 that separates genuine quantum entanglement from anything a classical system reproduces, and that separation held for the entire 20-plus-hour window, not a brief peak measurement.
What this validates, and what it does not
The result is evidence that metropolitan-scale quantum networks, QKD channels, and distributed quantum computing interconnects are deployable on existing, unshielded commercial fiber, without requiring new underground infrastructure built specifically for quantum signals. That is a meaningfully different claim from showing entanglement is possible over 62 km in principle, which has been demonstrated before under more controlled conditions. It is not, on its own, a demonstration of a working QKD system or a distributed computing link. Entanglement distribution is the underlying primitive those applications need, not the finished application itself, similar to how Quantum Corridor, Ciena, and Toshiba's live PQC-plus-QKD trial demonstrated encryption at commercial speed on production fiber a day earlier without claiming to have solved every part of quantum-safe networking at once.
What to watch next
The test for this result is whether Qunnect's polarization-compensation approach gets deployed on a fiber route carrying live QKD or distributed quantum computing traffic, rather than staying a research demonstration between two university campuses. Our quantum networking piece covers how entanglement distribution, QKD, and distributed quantum computing interconnects fit together as separate but related pieces of the same infrastructure problem.