Human eye can detect individual photons

Scientific American (July 19) -- People can detect flashes of light as feeble as a single photon, an experiment has demonstrated—a finding that seems to conclude a 70-year quest to test the limits of human vision. A new study, published in Nature Communications, “finally answers a long-standing question about whether humans can see single photons — they can!” says Paul Kwiat, a quantum optics researcher at Illinois who was not involved in the study. The techniques used in the study also open up ways of testing how quantum properties—such as the ability of photons to be in two places at the same time—affect biology, he adds. Also: Nature (July 19).