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.
The study, published in Nature Communications on July 19, “Finally answers a long-standing question about whether humans can see single photons – they can!” says Paul Kwiat, a quantum optics researcher at the University of Illinois at Urbana-Champaign.
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.
Experiments on cells from frogs have shown that sensitive light-detecting cells in vertebrate eyes, called rod cells, do fire in response to single photons. In June 2015, physicist Rebecca Holmes, who works with Kwiat, reported evidence that humans can sense light flashes containing as few as three photons. The three volunteers sat through a total of more than 2,400 trials in which a single photon was emitted.
Vaziri plans to test how the visual system responds to photons in various quantum states-in particular those that are in a ‘superposition’ of two simultaneous states.