NIST is developing a calibration protocol known as correlated photon radiometry to establish highly accurate measurement standards for quantum sensors and light detectors. Instead of relying on imperfect reference light sources, the method uses pairs of linked photons to independently verify detector accuracy. By tracking both individual detections and simultaneous events, researchers can calculate absolute efficiency measurements tied directly to fundamental physical constants. Initial testing has achieved 0.5% accuracy for visible-light detectors, with active improvements underway to reach 0.1%. This protocol is currently under validation, with streamlined versions already implemented in laboratory settings.
Alongside detector calibration, NIST is refining a multiplexed single-photon source protocol designed to reliably produce exactly one photon at a time—a critical requirement for quantum computing and secure communication networks. Traditional sources often struggle with producing multiple photons by mistake, but this new approach uses parallel light generators and optical routing to boost reliability while suppressing errors. A simplified version of the system is already in use, making it easier to verify true single-photon output. While no fixed rollout dates have been set, these standards are expected to gradually integrate into broader quantum measurement frameworks as testing continues, ultimately improving the precision, calibration consistency, and real-world reliability of emerging quantum technologies.
Source: https://www.nist.gov/pml/quantum-measurement-division/quantum-optics/correlated-photon-radiometry
Keywords: photon counting, quantum efficiency, parametric down-conversion