Stony Brook, Brookhaven Lab Researchers Demonstrate ‘Wireless’ Capability for Quantum Network

From left: Stony Brook University Professor Eden Figueroa with senior project manager Dimitrios Katramatos and PhD student Rishikesh Gokhale at Stony Brook's new Quantum Watchtower, a 375-square-foot facility atop the Health Sciences Center designed to advance wireless quantum networking. Photos by John Griffin.

First-of-its-kind free-space optical link begins quantum entanglement experiments

Researchers at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory and the State University of New York at Stony Brook (Stony Brook University) have successfully transmitted light particles containing quantum information through open air between the two institutions.

This is the first demonstration of its kind in the United States and a key milestone toward extending the nation's longest quantum network - already connecting eight nodes across several institutions - beyond the limits of fiber-optic cables.

"The future of quantum information science will depend not only on what individual quantum computers and devices can do but on our ability to connect them," said DOE Under Secretary for Science Darío Gil. "As DOE advances its Genesis Mission, we are building toward an interconnected research ecosystem where advanced computing, artificial intelligence and quantum technologies can work together to tackle some of our most complex scientific challenges. The capabilities demonstrated by Brookhaven Lab and Stony Brook University today are an important step toward making that vision possible."

During a daytime demonstration on August 21, researchers used a laser to generate quantum states of light, each containing just a few individual photons, in Stony Brook University's state-of-the-art Quantum Watchtower. From the Watchtower, located on the roof of Stony Brook's Health Sciences Center in Stony Brook, New York, the photons exited the core of an optical fiber only about five microns in diameter - less than one-tenth the width of a human hair - and traversed 13 miles (21 kilometers) to Brookhaven's Quantum Lighthouse in Upton, New York.

In the Lighthouse, Gil cut a ribbon blocking the receiving aperture, allowing the photons to reach the detector. Researchers and distinguished guests gathered in the Quantum Lighthouse - built on top of the only Brookhaven Lab building with a clear line of sight to Stony Brook University - to watch as an ultrafast camera marked the photons' arrival in an equally small optical fiber.

The daytime demonstration showcased the extraordinary precision of this free-space optical (FSO) link between the two institutions, with researchers transmitting photons between fiber-optic cables that are only a fraction of a millimeter in diameter and separated by several miles. But the team has already progressed to the next phase of experimentation using entangled photons - pairs of light particles that are intrinsically linked by the laws of quantum mechanics.

During nighttime tests, when there are lower levels of background light, the researchers successfully sent entangled photons from the Stony Brook physics laboratory to the Quantum Watchtower via fiber, then distributed them across the new FSO link, and successfully received and measured them at the Quantum Lighthouse. This is a key advance toward achieving sustained "wireless" exchange of quantum information between the two institutions, and eventually beyond.

A map shows Brookhaven National Laboratory, Stony Brook University, and Yale University - the three institutions hosting facilities that form the free-space optical (FSO) link. The FSO link, used to transmit particles of light containing quantum information between institutions, adds a wireless component to the nation's longest quantum network. (Jennifer Abramowitz/Brookhaven National Laboratory)

The FSO link - which includes the Quantum Lighthouse and Quantum Watchtower, along with a third facility under development at Yale University in New Haven, Connecticut - adds a wireless component to the record-setting quantum network currently spanning 161 miles and several institutions across Long Island and the New York metropolitan area.

Using this network, pioneered by Stony Brook and Brookhaven Lab, researchers can transmit entangled photons through commercial fiber. Because the particles remain entangled even when separated by long distances, measuring one photon instantly reveals information about its counterpart. This property, often referred to as "spooky action at a distance," is key for the future of ultra-secure communications, advanced quantum sensing, and networked quantum computing.

"In our long-distance fiber network, we routinely transmit entangled pairs of photons. However, such fiber networks are limited to the use of telecom wavelengths. In our new quantum wireless links, we are exploring the use of infrared wavelengths that are native to quantum processors and related technologies," said Eden Figueroa, director of Stony Brook's Quantum Institute, endowed presidential professor of physics in the Department of Physics and Astronomy in the College of Arts and Sciences, and a joint appointee at Brookhaven Lab. "This will provide a direct route to create entangled atomic systems across long distances."

From left: Guodong Cui, postdoctoral associate; Samet Demircan, PhD candidate; and Rishikesh Gokhale, PhD student building the FSO telescope at Stony Brook.

"Extending our quantum communication network to include a wireless link is a major leap forward in our development of the Quantum Internet of Things," said Stony Brook University President Andrea Goldsmith. "I'm thrilled that our brilliant Stony Brook researchers, together with our partners at Brookhaven National Laboratory, have demonstrated impressive progress in overcoming the significant challenges of sending quantum information wirelessly via entangled photons. By unlocking wireless quantum connectivity and incorporating it into the world's only metropolitan-area network that supports quantum communication via entanglement, we are transforming secure data transmission while igniting Long Island as an innovation hub. We are profoundly grateful to our elected officials, Governor Hochul, Senator Schumer, Senator Gillibrand, and Rep. LaLota for their generous support and for securing investments in Long Island's quantum research. Ultimately, this places New York State at the forefront of quantum information science and its application to secure communication for finance, healthcare, and cybersecurity."

Building the FSO link

In some ways, the classical internet's evolution from wired connections to a complex network of wired and wireless technologies provides a roadmap for reaching milestones toward a global quantum network. But the researchers also needed to draw on expertise from a seemingly unrelated field: astronomy.

Today's classical wireless technologies, including cell phones and orbiting satellites, use radio frequencies to transmit information without a physical connection. But radio frequencies are far too noisy to preserve fragile quantum information. Instead, the researchers turned to optical light for sending quantum signals through open air.

"People think of telescopes as tools for looking up into space, but the same technologies that allow astronomers to precisely collect and control light are essential for these quantum experiments," said Justine Haupt, Brookhaven Lab's lead scientist on the cross-institutional FSO link project.

Video: At 12:26 a.m. ET on Wednesday, Aug. 19, researchers at Brookhaven Lab's Quantum Lighthouse detected entangled photons arriving from Stony Brook's Quantum Watchtower. The graph's uptick on the far right around 0:37, coinciding with the "Entanglement Source ON" text, marks the arrival of entangled photons. (Brookhaven National Laboratory)

Haupt and her colleagues at Brookhaven are experts when it comes to telescopes, having built key components for several high-profile astronomy projects. But because there is more turbulent atmosphere between Brookhaven Lab and Stony Brook University than there is between Earth and the stars, the scientists needed to develop technology sophisticated enough to ensure the photons could travel between institutions without becoming distorted or losing their fragile quantum information. But that was only one piece of a much larger puzzle.

"Both Brookhaven and Stony Brook needed to build specialized rooftop facilities for the telescope systems that were optimized for quantum experiments," Haupt said. "We needed to integrate the optics, controls, communications, quantum sources, and detectors so equipment 21 kilometers apart could operate as one experiment. Bringing all those pieces together - and then adding the quantum layer - is what makes this capability unique."

"New York State is committed to investing in cutting-edge research and innovation in emerging fields that move our society forward," said New York Governor Kathy Hochul. "The partnership between the State University of New York at Stony Brook and Brookhaven National Laboratory serves as an excellent example of how collaboration can advance discovery and create transformative technologies."

Looking ahead

Yale's facility - the third leg of the FSO link - was recently completed, and the researchers will soon begin establishing the Stony Brook-Yale connection so they can also transmit entangled photons 30 miles (48 kilometers) across the Long Island Sound.

"While completing this longer leg, the team is simultaneously moving toward one of our ultimate goals: transmitting quantum information through Earth's atmosphere to orbiting satellites," said Brookhaven Lab Associate Laboratory Director for Discovery Technologies Gabriella Carini. "Incorporating satellites into the network could help bring secure quantum communications to rural or remote locations with minimal ground-based telecommunications infrastructure, transforming the quantum network from a regional one to a global one."

Expanding beyond the limits of fiber also opens the door to new kinds of quantum experiments by enabling researchers to use photons with wavelengths, or "colors," different from the telecommunications wavelengths optimized for commercial fibers. Many quantum technologies naturally operate at these other wavelengths, making free-space links a promising path toward linking quantum devices across long distances. Researchers ultimately envision using the FSO link to connect quantum computers at Brookhaven and Stony Brook - and beyond - enabling them to work together and tackle some of the nation's most pressing scientific challenges.

"Brookhaven has long been at the forefront of quantum information science, and this achievement represents another important step in that journey," said Brookhaven Lab Director John Hill. "This free-space link is a key milestone in its own right, but it is also part of a much larger roadmap leading to distributed quantum systems. We will continue advancing the network's capabilities so that researchers can connect increasingly sophisticated quantum systems together to address a range of problems, from computation to communication to sensing, in ways that just aren't possible today."

"Under Secretary Gil's return to Brookhaven National Lab is another reminder that some of the world's most important scientific work is happening right here in Suffolk County," said U.S. Rep. Nick LaLota. "Quantum research will play a major role in shaping the technologies we rely on every day, while strengthening our national security and ensuring America remains at the forefront of scientific innovation. At a time when Washington must spend taxpayer dollars wisely, I'm focused on prioritizing smart, targeted investments in projects and partnerships at Brookhaven and Stony Brook that support good-paying Long Island jobs, advance groundbreaking research, and keep America leading the world in innovation."

"Long Island has long been home to some of the world's most important scientific institutions, and today's milestone demonstrates what is possible when those institutions work together," said Empire State Development Board Chairman and Stony Brook Council Chair Kevin Law. "The partnership between Stony Brook University and Brookhaven National Laboratory is helping establish Long Island as a leader in quantum technology and positioning the region to attract talent, investment, and future economic growth for years to come."

The work at Brookhaven Lab is primarily supported by the DOE Office of Science. At Stony Brook University, the work is supported by the National Science Foundation and New York's Empire State Development.