Researchers at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Stony Brook University (SUNY) have demonstrated the first permanent free-space optical (FSO) quantum link in the United States. Operating between Stony Brook’s Quantum Watchtower and Brookhaven’s Quantum Lighthouse, the team transmitted single photons and entangled photon pairs through 13 miles (21 kilometers) of open atmosphere, adding a “wireless” leg to the nation’s longest metropolitan quantum network.
| [ Long Island Free-Space Quantum Network Architecture ] | ||
|---|---|---|
| Watchtower (SBU) | FSO Optical Link | Lighthouse (BNL) |
| • 5 µm Core Fiber Photon Emitter | • 13-Mile (21 km) Open-Air Path | • 0.6m Mirror Telescope Collector |
| • Entangled Photon Pair Source | • Real-Time Atmospheric De-Crinkling | • Ultra-Fast Single-Photon Camera |
| • Infrared Channels | • kHz Deformable Mirror Corrections | • Direct-Fiber Re-Focusing (5 µm core) |
Atmospheric Adaptive Optics and Entanglement Transmission
Transmitting unguided single photons across low-altitude, turbulent ground-layer atmosphere presents significant engineering challenges. Thermal variation, wind, and ground structures distort light wavefronts, causing loss of spatial coherence and single-photon coupling failures:
- Telescope & Adaptive Optics Integration: Developed by Brookhaven’s Instrumentation Department (drawing on astronomical telescope designs from the Vera C. Rubin Observatory), the system expands a 5-micron fiber core output to a 25-inch (0.6-meter) primary mirror beam. Deformable mirrors operating at kilohertz frequencies execute real-time adaptive optics corrections to counter atmospheric turbulence before focusing the light back into a 5-micron fiber core at the receiving end.
- Infrared Quantum Wavelengths: Unlike commercial optical fiber networks that mandate telecom-band wavelengths (∼1550 nm), free-space optical links can transmit infrared wavelengths native to atomic systems and physical quantum processors, establishing a direct channel to entangle remote atomic memories without wavelength conversion overhead.
- Daytime & Nighttime Entanglement Verification: On August 19, 2026, at 12:26 a.m. ET, the Lighthouse recorded the arrival of entangled photon pairs sent from the Watchtower across the FSO link. The team subsequently demonstrated daytime precision transmission, validating single-photon optical tracking and beam stabilization.
Expansion to Yale University and Orbital Satellites
The 13-mile Stony Brook–Brookhaven FSO link integrates directly into the existing 161-mile, eight-node Long Island fiber-optic quantum network. The milestone forms part of a broader infrastructure expansion:
- Stony Brook–Yale Node Connection: A third identical optical facility has been constructed at Yale University in New Haven, Connecticut. The team is preparing to establish a 30-mile (48-kilometer) free-space entanglement link across the Long Island Sound, bridging New York and Connecticut quantum nodes.
- Quantum Internet of Things & Satellites: Led by Stony Brook Quantum Institute Director Dr. Eden Figueroa and BNL Scientist Justine Haupt, the team will use the rooftop telescope infrastructure to track classical and quantum low-Earth orbit (LEO) satellites, laying ground-station groundwork for global satellite-based quantum key distribution (QKD) and distributed quantum computing.
Supported by the DOE Office of Science, the National Science Foundation (NSF), and New York’s Empire State Development (which funded the $300 million SUNY Stony Brook Quantum Innovation Hub), the accomplishment advances regional distributed quantum networks under the DOE Genesis Mission framework.
Review the joint announcement on the Brookhaven National Laboratory Newsroom here, read the feature on BNL QIST News here, explore state updates via SUNY Stony Brook News here, and examine policy details via Governor Hochul’s Press Office here.
August 21, 2026