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QUANTUM IS IN THE EYE OF THE BEHOLDER
Figure 1. Quantum technologies may usher in a new way of performing measurements of the eye while ensuring secure transmission. Light controlled at its ultimate quantum level can be prepared in a state showing entanglement, i. e. a connection among its constituents beyond what is possible by purely classical means. These correlations can be so strong that, while the overall state is specified, each partition carries limited information. This is only retrieved when access is granted to the whole state. Measurement performed remotely by Alice on Bob’ s eye can thus be made secure by the use of entangled photons since verifying the integrity of their correlations provides a way to certify the integrity of the measurement itself using protocols of quantum cryptography. Light can thus serve as the means to observe and encrypt at the same time.
RETINA AS A DETECTOR
The eye can be considered as a detector with its entrance focussing elements( the cornea and the crystalline lens) and an active layer. This is composed of receptor cells containing rhodopsin or iodopsin molecules that undergo activation upon absorption of light by a phototransductive mechanism. This signal is conveyed to the brain via the optical nerve, but it passes first through a network of specialized neural cells. Different kinds of photoreceptors have a distinct spectral response and their density changes with the relative position to the central region of the fovea. limited available time, an accurate reconstruction can be achieved. It could be interesting to extend those considerations also to the spatial domain, envisaging techniques to infer the spatial distribution of lowlight sensitivity in individuals. Many ocular pathologies, especially those affecting the retina and the optical nerve, become manifest as alterations of vision with the appearance of blind spots. Typically, the disease at its onset exhibits a distinct spatial profile of the alteration. Tests at very low illumination levels that have access to the spatial resolution on the retina may uncover such pathologies at an earlier stage.
Loulakis and coworkers have introduced the intriguing idea of using quantum parameter estimation as a tool for biometric recognition [ 9 ]. Their original idea concerned the estimation of the transmissivity of the ocular medium as a marker based on“ the photon-counting principles of human rod vision” [ 10 ]. This concept can also be extended to other ocular structures, such as the corneal surface or specific spatial characteristics of the pupillary frill and the optic nerve on the retina. Differently from the usual setting in quantum sensing, however, this valid proposal is faced with the challenge of taking into account the natural variability of those parameters. For instance, the opacity of the eye media is influenced by hydration. A good balance should be found between the required accuracy and precision demanded by biometry on the one side and the tolerance demanded by physiology.
The appeal of quantum light in such applications not only resides in its sensing power but also in the fact that it may become possible to combine the recognition protocol with secure data transmission. Controlling the quantum state of light is the key aspect that permits improved performance for precision measurement, but also what ensures security in quantum cryptography. Combining the two tasks in one system taking up
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