Research by a team from Rockefeller University and the Research Institute of Molecular Pathology in Austria has recently shown that humans can detect the presence of a single photon, the smallest measurable unit of light. Previous studies had established that human subjects acclimated to the dark were capable only of reporting flashes of five to seven photons. The new work was led by Alipasha Vaziri, Ph.D., Associate Professor and Head of the Laboratory of Neurotechnology and Biophysics at Rockefeller and an adjunct investigator at the Research Institute of Molecular Pathology. The work was published online on July 19, 2016 in Nature Communications. The open-access article is titled “Direct Detection of a Single Photon by Humans.” “If you imagine this, it is remarkable: a photon, the smallest physical entity with quantum properties of which light consists, is interacting with a biological system consisting of billions of cells, all in a warm and wet environment,” says Dr. Vaziri. “The response that the photon generates survives all the way to the level of our awareness despite the ubiquitous background noise. Any man-made detector would need to be cooled and isolated from noise to behave the same way.” In addition to recording the ability of the human eye to register a single photon, the researchers found that the probability of doing so was enhanced when a second photon was flashed a few seconds earlier, as if one photon “primes” the system to register the next. Previous experiments designed to test the human eye’s sensitivity have suffered from a lack of appropriate technology, Dr. Vaziri says. “It is not trivial to design states of light that contain exactly one or any other number of photons,” he says. “This is because the number of photons in a classical light source such as that from a lamp or a laser follow certain statistical distributions.
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