Quantum jump photodetector picks out single photon signals amidst sunlight

Detecting weak optical signals against the overwhelming light of the sun is necessary for daytime use of LIDAR and free-space optical communications. Historically, these applications have been limited to nighttime uses as the detection of such signals relied on narrow filters and was extremely difficult.

But that’s changing with a quantum jump photodetector tested by Zarraoa et al. Continuing their previous work developing the device, the authors tested the photodetector in daylight and found it could pick out a single photon signal amidst billions of solar photons.

The photodetector uses a single rubidium-87 atom trapped in an optical tweezer. When a signal photon reaches the atom, the atom absorbs the photon, which triggers a strong fluorescence signal that is picked up by four lenses surrounding the atom. The rubidium atom was chosen because its internal transition occurs at 780 nanometers, matching the infrared range that LIDAR and free-space communications typically use for signaling.

To test the detection, the researchers used a telescope to gather sunlight, which was then fed into a lab with fiber optic cables. The signal light was combined with the sunlight in a beam splitter before being shined at the photodetector. The results showed the signal was detected even when embedded in tens of nanowatts of sunlight. A rate-equation model for the atom confirmed the experimental results.

“In a period where many quantum technologies emerge, our work demonstrates that current technology using single atoms trapped in optical tweezers could benefit demanding applications such as low-light detection in daylight,” said author Romain Veyron. “We hope that our demonstration will motivate the development and the use of atomic photodetectors.”

Source: “Detection of photon-level signals embedded in sunlight with an atomic photodetector,” by Laura Zarraoa, Tomas Lamich, Sondos Elsehimy, Morgan W. Mitchell, and Romain Veyron, AVS Quantum Science (2026). The article can be accessed at https://doi.org/10.1116/5.0314886 .