NIST just proved quantum signals can survive 38 miles of ordinary, above-ground cable

[EventHorizon Crossing]

Researchers at the US National Institute of Standards and Technology successfully transmitted entangled photons across 62 kilometers. About 38.5 miles, of existing network cabling without breaking their delicate quantum entanglement, in what physicist Yicheng Shi calls a deliberate stress test of quantum networking systems under genuinely harsh real world conditions.

What makes this notable isn't the raw distance, which isn't actually a record, it's the setup. Much of the fiber optic cable involved ran above ground rather than buried, strung between street side poles connecting NIST and a nearby university, meaning the fragile quantum signals had to survive constant exposure to wind, temperature swings, and vibration from traffic and even passing birds, conditions Shi bluntly describes as about as bad a connection as you can possibly have.

Entangled particles exist in a quantum superposition that collapses the moment they're measured, and that fragile quantum state is easily distorted by exactly the kind of environmental interference above ground cabling constantly experiences, changes that scramble the photons' polarization, the specific property carrying the actual entanglement information. To work around that interference, the researchers used a reference laser light signal alongside the quantum data to help correct for environmental noise without disturbing the fragile entangled state itself.

This builds on a broader wave of real world quantum networking demonstrations reported this year. Northwestern University researchers separately sent entangled photons through a 24.4 kilometer fiber connecting Evanston and downtown Chicago while that same cable simultaneously carried live commercial internet traffic, preserving entanglement with more than 94% fidelity, and University of Pennsylvania researchers demonstrated quantum signals travelling over commercial Verizon fiber using the same Internet Protocol that runs the ordinary web.

Shi frames the actual significance plainly. This is a demonstration that quantum networking protocols can work in real world environments, not just in a controlled laboratory setting, which matters enormously for the practical question of whether a genuine future quantum internet could actually piggyback on infrastructure that already exists rather than requiring an entirely new dedicated physical network built from scratch

The Quantum Internet Just Passed Its Toughest Real-World Test Yet - Over 38 Miles of Ordinary Cablewww.sciencealert.com