A New Lighthouse on Long Island
There is a new lighthouse on Long Island, but it does not guide ships. Perched atop a seven-story building at the U.S. Department of Energy's Brookhaven National Laboratory, the "Quantum Lighthouse" transmits and receives particles of light carrying quantum information. It is a key pillar of a free-space optical (FSO) link spanning Brookhaven Lab, Stony Brook University, and Yale University.
Justine Haupt, Brookhaven Lab's lead scientist on the cross-institutional FSO link project, explained its significance: "An FSO link is analogous to the wireless technology that allowed today's classical internet to expand beyond wired connections to orbiting satellites, as well as our cellphones. It's one of the key technologies needed to make a quantum internet truly useful."
The First Permanent Link of Its Kind
This FSO link—described as the first permanent one of its kind—adds a wireless component to the nation's longest quantum network. That network spans 161 miles (259 kilometers) across Long Island and the New York metropolitan area. Through it, researchers transmit entangled photons: pairs of light particles linked by quantum mechanics, even over distances. Measuring one instantly reveals information about its counterpart, a unique property with potential for ultrasecure communications, advanced quantum sensing, and networked quantum computing.
With the FSO link operational, researchers can send entangled photons 13 miles (21 kilometers) through the air between the Quantum Lighthouse in Upton and Stony Brook University's Quantum Watchtower in Stony Brook. A third identical facility at Yale University in New Haven, Connecticut, will soon begin operations, enabling transmission of entangled photons 30 miles (48 kilometers) across the Long Island Sound.
Engineering Against Turbulence
Transmitting quantum information through open air poses challenges, primarily atmospheric turbulence and ground-level heat. To counter this, the researchers use adaptive optics technology that corrects for turbulence in real time. Thin mirrors, warped thousands of times per second, "uncrinkle" the light as it travels. The technique expands the beam from 5 microns to 25 inches in diameter before it traverses, ensuring photons reach their destination intact—visible from the seven-story building at Brookhaven.
"These are incredible engineering feats," said Eden Figueroa, a researcher involved in the project, lauding the innovative approach. "By expanding the beam, we can compensate for distortions over long distances." Gabriella Carini, another team member, added that this is "the first permanent free-space link to be incorporated into a quantum network, allowing us to test real-world applications."
Looking Ahead
Currently, operations run at night, when atmospheric conditions are more stable. The team has set its sights on enabling all-weather transmission, which would make the system more robust. Plans also include incorporating a satellite into the network in the future, further extending quantum connectivity.
The new FSO link represents a step toward a practical quantum internet—an infrastructure that could leverage quantum properties for ultrasecure data transmission. As Haupt noted, this is one of the key technologies needed to make a quantum internet truly useful.
A United Effort
Three institutions are involved: Brookhaven National Laboratory (DOE), Stony Brook University, and Yale University. The collaboration underscores the regional scope of the effort, with each node contributing to the network's capacity.
--