A quantum signal has completed a difficult journey through 62 kilometers of aerial fiber in the Maryland suburbs, surviving the vibrations, temperature changes and movement that normally make overhead telecommunications lines hostile to delicate quantum information. The achievement, reported by researchers at the National Institute of Standards and Technology (NIST), the Joint Quantum Institute and quantum technology company Qunnect, is being viewed as an important real-world test of a technology that could eventually connect quantum computers, sensors and secure communication systems into a global network.
Quantum networks rely on entanglement, one of the most counterintuitive features of quantum mechanics. When two particles become entangled, they share a single quantum state and cannot be fully described as independent objects, even after being separated by long distances. Measuring one particle establishes the corresponding outcome for the other. Although entanglement does not allow information to travel faster than light, it provides correlations that have no classical equivalent and could become the foundation of future quantum communication and distributed computing.
The potential applications are enormous. Entangled telescopes separated by thousands of kilometers could one day combine their observations of distant stars and planets, creating images with far greater resolution than a single telescope could produce. Networks of entangled sensors might detect minute disturbances caused by earthquakes, volcanic activity or underground movement. Quantum computers linked together could share computational tasks that exceed the capacity of any individual machine, opening new possibilities for simulating chemical reactions, designing materials and identifying promising drug candidates.
Before any of those applications become practical, however, researchers must solve a basic problem: quantum states are extraordinarily fragile. The Maryland experiment focused on photons, particles of light whose quantum information was encoded in polarization—the direction in which the electric field oscillates. In a conventional fiber-optic network, small mechanical disturbances are usually insignificant because classical data is transmitted by changing the intensity or power of the light. Quantum information encoded in polarization is much more vulnerable to physical changes in the fiber.
The researchers deliberately used fiber suspended from utility poles, rather than a carefully shielded cable buried underground. During the day, the fiber expands as it warms; at night, it contracts. Wind causes the cable to sway, while birds and other environmental influences add further disturbances. These changes can twist the fiber and transform the polarization of photons traveling through it. If the transformation is not corrected, the relationship between entangled photons can become scrambled, destroying the quantum correlations needed by the network.
“It’s about as bad a connection as you can possibly have,” said NIST physicist Oliver Slattery, one of the study’s authors. The exposed route effectively turned the experiment into a stress test for quantum networking. Instead of building a specialized quantum network from scratch, the team asked whether existing infrastructure—much of it designed for ordinary internet traffic—could be adapted to carry entangled states without requiring constant manual adjustment.
The experiment began with a commercial device that generated pairs of entangled photons. One photon from each pair remained in a NIST laboratory, where its polarization was measured. The other photon traveled through approximately 62 kilometers, or 38.5 miles, of fiber to a second laboratory at the University of Maryland in College Park. The two photons began with linked polarization states, so measurements made at the two locations could later be compared to determine whether their entanglement had survived the journey.
To compensate for the changing fiber, the researchers used a pair of polarization-stabilization devices developed by Qunnect. These systems sent reference light through the same fiber path as the quantum signals. At the receiving end, the devices measured how the fiber had altered the reference light’s polarization. The system then calculated the inverse of that transformation and applied the correction to the quantum photons in real time. In effect, the equipment continuously tracked the fiber’s behavior and attempted to undo its effects before the fragile quantum correlations were lost.
The system transmitted about 1,500 entangled photons per second. Over a 24-hour period, entangled photons were successfully distributed 92.8% of the time, while polarization corrections were required during the remaining 7.2%. Statistical testing confirmed that the photons detected at the two ends retained correlations consistent with entanglement. The result did not surpass the 248-kilometer record set by a European team using underground fiber in 2022, but it addressed a different and highly practical challenge: whether quantum networking can function on infrastructure exposed to the everyday forces of the environment.
Yicheng Shi, the NIST physicist who led the study, described the experiment as an extreme test of quantum networking protocols. The successful transmission suggests that future quantum networks may not require entirely separate fiber systems, potentially reducing the cost and complexity of deployment. The researchers emphasize that major hurdles remain, including improving transmission rates, extending distances, reducing losses and developing quantum repeaters capable of preserving entanglement across much larger networks. Even so, the demonstration shows that the road to a quantum internet may run not through pristine laboratory equipment, but along the same aerial cables already carrying the world’s digital traffic.
Subject of Research: Quantum entanglement and quantum networking
Article Title: Entanglement Distribution Over a Polarization-Stabilized Aerial Fiber
Web References: https://doi.org/10.1364/JOCN.592521
References: Yicheng Shi, Jing Su, Anouar Rahmouni, Pranish Shrestha, Mheni Merzouki, Gabriel Bello Portmann, Anne Lazenby, Mael Flament, Mehdi Namazi, Abdella Battou, Oliver Slattery and Thomas Gerrits, “Entanglement Distribution Over a Polarization-Stabilized Aerial Fiber,” Journal of Optical Communications and Networking, published online July 15, 2026. DOI: 10.1364/JOCN.592521
Image Credits: N. Hanacek/NIST
Keywords
Quantum entanglement, quantum networking, quantum internet, quantum optics, polarization stabilization, entangled photons, aerial fiber, quantum communication, NIST, quantum computing
