Speaker
Description
Emerging photo-detection applications, including ‘light-shining-through-walls’ experiments to search for new particles and interplanetary optical communications, require photodetection with extremely low dark counts and strong background rejection. Here background rejection means filtering to prevent unwanted light (back- ground light) from reaching the photon counting devices. For many contemporary applications, background light comes mainly from the sun: either directly because the photodetector is exposed to sunlight, or indirectly as in the photodetector does not look directly at the sun but is exposed to skylight, which is sunlight scattered from Earth’s atmosphere. In [1], we demonstrated a narrowband quantum jump photodetector (QJPD) to detect single-photons based on a single cold atom and quantified its experimental quantum efficiency and dark count rate. Here, we present the performance of the QJPD in the presence of strong broadband background [2].
The photon counting capabilities of the QJPD under direct and indirect broadband excitation are tested, by measuring quantum jump rates when the atom is illuminated with direct sunlight, and with light scattered by the atmosphere (skylight). A rate equation model is developed to describe QJ probabilities in the presence of both intense broadband background and weak resonant probe light. This model is used to interpret
experiments in which a weak signal beam competes with strong broadband background and validated using sunlight, demonstrating a reliable method to extract probe photon numbers even in the presence of background. Measurements where the atom is illuminated with skylight show no observable background-induced QJs.
