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Physics Today

Physical Limits to the Performance of Imaging Systems

Albert Rose, PAUL K. WEIMER

Published Sep 1, 1989• 32 citations
Publisher

Abstract

Our visual system provides our principal contact with the world around us. This system, thanks to millions of years of natural development, achieved a high degree of perfection long before humans arrived on the scene. To attain such perfection, these evolutionary processes had to recognize the quantum nature of light—a remarkable accomplishment.

DOI
10.1063/1.881180

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Our visual system provides our principal contact with the world around us. This system, thanks to millions of years of natural development, achieved a high degree of perfection long before humans arrived on the scene. To attain such perfection, these evolutionary processes had to recognize the quantum nature of light—a remarkable accomplishment.
A study published in Nature Communications demonstrated for the first time that humans can consciously detect a single light particle by directing a single photon, controlled by quantum optical technology (SPDC), onto the cornea of human subjects. Breaking the conventional wisdom regarding the necessity of multiple photons for perception, the study showed that subjects directly perceived a single photon with a probability significantly above statistical chance. The study discovered a priming process where the probability of detecting a second single photon is significantly enhanced for several seconds after detecting an initial single photon, proving that the human visual neural network is a marvelous system capable of filtering information at the absolute quantum limit. [Quantum Biology Society] How fine a physical stimulus can human senses detect? In particular, whether our vision, through which we see the world, can perceive the most fundamental physical limit—a single particle of light (single photon)—has been a major subject of debate in the scientific community for over 70 years. While it was known that a single photoreceptor (rod cell) in the retina responds to individual photons , it was conventionally believed that to consciously perceive light, at least a few photons must arrive simultaneously to overcome noise. However, a phenomenal study has been published proving that the human eye and brain can break through this absolute quantum mechanical limit. The paper titled "Direct detection of a single photon by humans," published as an open-access article in the international journal Nature Communications, provides an answer to this fundamental question. A research team led by Professor Alipasha Vaziri and Jonathan N. Tinsley from the University of Vienna, the Research Institute of Molecular Pathology (IMP) in Austria, and The Rockefeller University in the USA, successfully spearheaded this groundbreaking experiment. ■ A Single Shot of Light Created with Quantum Optical Technology To overcome the limitations of conventional light sources, the research team utilized a quantum optical technology called spontaneous parametric down-conversion (SPDC). Through this, they built a perfectly controlled heralded single-photon source and performed over 30,000 rigorous psychophysics-based experimental trials, shooting this single photon into the corneas of subjects inside a pitch-black dark chamber. ■ The Human Brain Performs Quantum Noise Canceling The results were astounding. The subjects accurately identified when a single photon was emitted with a probability significantly above statistical chance. Even though only a minuscule amount of quantum energy struck the retina, the human visual system and neural networks in the brain filtered this absolute minimum unit of information out of macroscopic noise and visually perceived it. ■ A Light Seen Once is Seen Better: The Priming Effect of the Visual System Even more interestingly, the researchers discovered that the probability of detecting a second single photon was temporarily and significantly enhanced within a time window of a few seconds immediately after a subject detected an initial single photon. The researchers analyzed this as a priming process where the presence of an earlier photon temporarily enhances the effective gain of the visual system. This study proves that a living organism's sensory organs are not merely chemical sensors but sophisticated biophysical systems that interact directly with the quantum world, the smallest unit in the natural world. This discovery provides a new understanding of the signal processing mechanisms of brain neural networks and is expected to open the door to entirely new research exploring human vision and the brain using quantum states of light. https://www.nature.com/articles/ncomms12172
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