New free-space optical link adds a wireless component to the nation's longest quantum network
There's a new lighthouse on Long Island. But instead of shining light to guide ships through waterways, this one transmits and receives particles of light that carry quantum information. Perched atop a seven-story building at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory, the "Quantum Lighthouse" is a key pillar of the free-space optical (FSO) link spanning Brookhaven Lab,…
A groundbreaking free-space optical (FSO) link has been added to the nation's longest quantum network, spanning 161 miles (259 kilometers) across Long Island and the New York metropolitan area. This wireless component, installed at the U.S. Department of Energy's Brookhaven National Laboratory, enables researchers to transmit entangled photons over 13 miles (21 kilometers) through the air between Brookhaven's Quantum Lighthouse and Stony Brook University's Quantum Watchtower.
Quantum entanglement is a unique property of quantum mechanics, where measuring one photon instantly reveals information about its counterpart, even when separated by long distances. This could enable applications such as ultrasecure communications, advanced quantum sensing, and networked quantum computing.
The Quantum Lighthouse, perched atop a seven-story building, is a key component of the FSO link. Researchers generate entangled photons at network nodes by shining a laser into a specially designed crystal or optical device. Once these particles reach FSO link nodes, telescopes are used to transmit the light, as fiber cannot be relied upon for such long distances.
Adaptive optics technology, originally developed for ground-based telescopes, is employed to correct for atmospheric distortions that crinkle the light's plane as it travels through the turbulent ground layer. This technology involves rapidly changing mirrors to uncrinkle the light, producing a clear final image. The adaptive optics system must make even more sophisticated corrections for the FSO link, considering the greater turbulence in the ground layer compared to the relatively calm space between Earth and celestial objects.
This new FSO link marks a shift from developing quantum devices in the laboratory to actively engineering large quantum systems. Researchers are now bridging their labs with deployed fiber and free-space optical quantum links, bringing Einstein's thought experiments of "spooky action at a distance" closer to reality, while establishing secure quantum networks and training the next generation of quantum professionals.
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