Daylight demonstration of low-light-level communication system using correlated photon pairs

Abstract
The authors demonstrate optical communication in free space at light levels much lower than that of ambient light. The method uses the highly time correlated nature of the photon pairs produced by non-degenerate parametric downconversion. Information was transmitted a distance of 200 m in daylight when the received signal intensity was only 0.14% of the detected background light level.