New study has found that the human eye can detect even the presence of a single photon. Previous research reported that humans are capable of sensing as few as three photons.
The capacity of a naked human eye cannot be underestimated.
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According to new research, the human eye is so sensitive to light that it can detect even a single photon – the smallest unit of light. This level of sensitivity is much higher than previously estimated. Even the most advanced technology designed to detect light fell short of reaching that level and requires noiseless controlled environment for doing so.
“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,” said lead researcher Alipasha Vaziri from Rockefeller University.
“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.”
Many experiments have been carried out to test the limit of human vision before. It was reported that human eye is capable of detecting light flashes containing as few as three photons. But these results lacked authenticity since no appropriate technology was available in the past to provide an accurate estimate.
To solve this problem, researchers have designed a special light source based on spontaneous parametric down-conversion or SPDC, which is a process often used in quantum optics. It produces two photons spontaneously. One of the photon was sent to human eye while the other was sent to a detector so scientists can estimate the time photon dispatched to an eye.
For the study, researchers involved three participants with excellent eyesight. They were asked to sit in total darkness for almost 40 minutes and to stare at an optical system. The experiment was started by pressing a button followed by two sounds with one separated by one second. Sometimes sound was accompanied by a photon while sometimes it was blank. Participants were asked to identify on which occasion they thought they saw a photon. Moreover, they had to rate how confident they were about their sighting on a scale of 1 to 3.
The participants got wrong in many cases but it was not unexpected. Researchers explained that almost 90% of photon could never reach the rod cells – the cells in the eye that detect light and were already absorbed or reflected by other parts of the eye. Still their guesses were more often right than not and confidence level was higher when they were right.
In more than 2,400 trials in which a photon was emitted, there were many instances when human eye was able to detect a single photon, providing strong statistical evidence of single-photon detection.
Next, researchers are planning to achieve the same feat in natural environment in the presence of noise.
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