In a new experiment by the National Institute of Standards and Technology (NIST), entangled photons successfully traveled about 38.5 miles through commercial fiber between Gaithersburg and College Park, Maryland. The project demonstrated that the fragile quantum connection can survive the noise and physical stresses of real-world communications infrastructure.
Albert Einstein famously described quantum entanglement as “spooky action at a distance,” a reference to the strange connection between particles that can remain linked even when separated. Nearly a century later, NIST researchers have taken steps to turn that strange phenomenon into working technology.
The NIST project is an important test for quantum networking because entanglement is difficult to preserve outside controlled laboratory conditions. Quantum networks could eventually connect quantum computers and communications systems, but they first need a reliable way to move entangled photons over long distances.
Using Existing Commercial Fiber
The NIST experiment used commercial fiber, much of it suspended from utility poles and exposed to wind and temperature changes. Those conditions create serious problems for quantum signals.
Traditional data networks are mostly tolerant of changes in the fiber because information is carried through variations in light intensity. Quantum networking often depends instead on photon polarization, which can be altered as fiber shifts, expands or contracts. If the polarization changes too much, the entangled state can be lost.
To deal with the real-world conditions, the research team used a real-time stabilization system developed by Qunnect. The system sent reference light through the network to detect changes in polarization and then made compensating adjustments to the quantum signals.
The approach worked. The researchers distributed about 1,500 entangled photons per second across the 62-kilometer link and recorded a 92.8% successful distribution rate. The stabilization system needed to correct polarization problems 7.2% of the time. Testing confirmed that the photons remained entangled after traveling across the network.
The experiment was recently documented in the Journal of Optical Communications and Networking.
Other researchers have sent entangled photons over longer distances. A European team previously demonstrated entanglement across 248 kilometers of underground fiber. But the NIST test was designed around a different problem: whether quantum networking could work over fiber exposed to the conditions found in ordinary telecom infrastructure.
That distinction matters economically as well as technically. Building entirely separate fiber networks for quantum applications would add substantial costs. If quantum networking can operate over existing commercial fiber, operators may be able to use infrastructure that is already in place.
The potential applications extend well beyond communications. Networks of quantum computers could allow multiple systems to work together on calculations too difficult for a single quantum machine. Researchers believe that could eventually support fields such as drug development and materials research.
