The retina is a light-sensitive layer is structured at the plane outer segments of an array of millions of individual nano-antennas. Apparently, the retina is one of the best known quantum detectors with rod cells able to respond to a single photon. It seems, the retina is an excellent photon counter and quantum processing of information occurs within the retina and subsequent processing of information at the level of neural membranes decrease the quantum efficiency. In this article we review on some evidences of quantum processing in the retina and finally propose some proposal experiments and ideas to detect quantum superposition in the retina.
The retina is a light-sensitive layer is structured at the plane outer segments of an array of millions of individual nano-antennas. Apparently, the retina is one of the best known quantum detectors with rod cells able to respond to a single photon. It seems, the retina is an excellent photon counter and quantum processing of information occurs within the retina and subsequent processing of information at the level of neural membranes decrease the quantum efficiency. In this article we review on some evidences of quantum processing in the retina and finally propose some proposal experiments and ideas to detect quantum superposition in the retina.
While looking for evidence of quantum coherent states within the brain, many quantum mind advocates proposed experiments based on the assumption that the coherent state of a photon entering the visual system could somehow be preserved through the neural processing, or in other words they suppose that photons collapse not in the retina, but in the brain cortex. In this paper we show that photons do collapse within the retina and subsequent processing of information at the level of neural membranes proceeds. Moreover, we explicitly stress on the fact that due to existent amplification of the signal produced by each photon, a basic quantum mechanical theorem forbids the photon state to be teleported from the retina to the brain cortex. The changes of the membrane potential of the neurons in the primary visual cortex are shown to be relevant to inputting visual sensory information that is already processed and is not identical to the visual image entering in the retina. A striking evidence for the existent processing of the incoming visual information by the retina is provided by visual illusions resulting from the lateral inhibition mechanism.
The two striking components of retina, i.e., the light sensitive neural layer in the eye, by which it responds to light are (the three types of) color sensitive Cones and color insensitive Rods (which outnumber the cones 20:1). The interaction between electromagnetic radiation and these photoreceptors (causing transitions between cis- and trans- states of rhodopsin molecules in the latter) offers a prime example of physical processes at the nano-bio interface. After a brief review of the basic facts about vision, we propose a quantum mechanical model (paralleling the Jaynes-Cummings model (JCM) of interaction of light with matter) of early vision describing the interaction of light with the two states of rhodopsin mentioned above. Here we model the early essential steps in vision incorporating, separately, the two well-known features of retinal transduction (converting light to neural signals): small numbers of cones respond to bright light (large number of photons) and large numbers of rods respond to faint light (small number of photons) with an amplification scheme. An outline of the method of solution of these respective models based on quantum density matrix is also indicated. This includes a brief overview of the theory, based on JCM, of signal amplification required for the perception of faint light. We envision this methodology, which brings a novel quantum approach to modeling neural activity, to be a useful paradigm in developing a better understanding of key visual processes than is possible with currently available models that completely ignore quantum effects at the relevant neural level.
The human eye contains millions of rod photoreceptor cells, and each one is a single-photon detector. Whether people can actually see a single photon|which requires the rod signal to propagate through the rest of the noisy visual system and be perceived in the brain|has been the subject of research for nearly 100 years. Early experiments hinted that people could see just a few photons, but classical light sources are poor tools for answering these questions. Single-photon sources have opened up a new area of vision research, providing the best evidence yet that humans can indeed see single photons, and could even be used to test quantum effects through the visual system. We discuss our program to study the lower limits of human vision with a heralded single-photon source based on spontaneous parametric downconversion, and present two proposed experiments to explore quantum effects through the visual system: testing the perception of superposition states, and using a human observer as a detector in a Bell test.
It was recently proposed to use the human visual system’s ability to perform efficient photon counting in order to devise a new biometric authentication methodology. The relevant “fingerprint” is represented by the optical losses light suffers along different paths from the cornea to the retina. The “fingerprint” is accessed by interrogating a subject on perceiving or not weak light flashes, containing few tens of photons, thus probing the subject’s visual system at the threshold of perception, at which regime optical losses play a significant role. The name “quantum biometrics” derives from the fact that the photon statistics of the illuminating light, as well as the quantum efficiency at the light detection level of rod cells, are central to the method. Here we elaborate further on this methodology, addressing several aspects like aging effects of the method’s “fingerprint,” as well as its inter-subject variability. We then review recent progress towards the experimental realization of the method. Finally, we summarize a recent proposal to use quantum light sources, in particular a single photon source, in order to enhance the performance of the authentication process. This further corroborates the “quantum” character of the methodology and alludes to the emerging field of quantum vision.
The rod photoreceptors in the retina are known to be sensitive to single photons, but it has long been debated whether these single-photon signals propagate through the rest of the visual system and lead to perception. Recently, single-photon sources developed in the field of quantum optics have enabled direct tests of single-photon vision that were not possible with classical light sources. Using a heralded source based on spontaneous parametric downconversion to generate single photons which were sent to an observer at either an early or late time, Tinsley and Molodtsov et al. (2016) had observers judge when the photon was seen. Based on the above-chance accuracy in both a subset of high-confidence trials and in all post-selected trials, they claimed to show that humans can see single photons. However, we argue that this work suffers from three major issues: self-contradicting results, inappropriate statistical analyses, and a critical lack of statistical power. As a result, we cannot conclude that humans can see single photons based on the data of this study. We present a careful examination of the statistical analyses and the internal consistency of the data, which indicated that none of the key evidence holds.
New tools and approaches of quantum optics offer a unique opportunity to generate light pulses carrying a precise number of photons. Accurate control over the light pulses helps to improve the characterization of photo-induced processes. Here, we interface a specialized light source which provides flashes containing just one photon, with retinal rod cells of Xenopus laevis toads. We provide unambiguous proof of single photon sensitivity of rod cells without relying on the statistical modeling. We determined their quantum efficiencies without the use of any pre-calibrated detectors, and obtained the value of 29+-4.7 %. Our approach provides the path for future studies and applications of quantum properties of light in phototransduction, vision, and photosynthesis.