Seeing subatomic particles with the naked eye

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Human vision can detect single photons or single particles of light, according to a new study showing it is possible for the naked eye to see a particle that is smaller than an atom. The Austrian and US researchers carried out over 30,000 particle-seeking tests on three participants, who either looked at a completely dark source or one that had just a single photon of light. The scientists found that although the participants didn't spot the photon every time, they did perform better than if it was just random chance.

Journal/conference: Nature Communications

Organisation/s: Rockefeller University, USA

Media Release

From: Springer Nature

Humans can detect single photons

Human vision can detect single photons with a probability above chance, reports a study published online this week in Nature Communications. This result provides new insights into the detection limits of the human eye.

Studies in the 1940s have established that human subjects are capable of reporting light signals as low as a few (five to seven) photons. However, whether humans can perceive a single photon has remained an open question, partly because of experimental constraints connected to the light source used to generate photons in previous experiments.

Alipasha Vaziri and colleagues designed a single-photon light source using quantum-optic technologies and test the detection limits of human vision in three participants. The light source system is capable of generating a correlated pair of photons: one photon was sent to the participant’s eye, and the other towards a highly-sensitive camera. During each trial, participants were presented with two light stimuli, one of which contained a single photon and the other was blank (in other words, it contained no light). Participants were asked to state which of the two stimuli contained a light signal. Based on the performance of the individuals across a total of 30,767 trials, the authors found that the averaged probability of the individuals correctly identifying a small flash of light containing a single photon from a blank is above chance.

The authors note that the retinal and brain-circuitry mechanisms underlying their findings are the scope of future work.


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