Photonic aspects of networks: from long-distance quantum networks to the brain

Abstract

Photons, the fundamental quanta of the electromagnetic field, travel at the fastest possible speed, and interact relatively weakly with the environment. These features make them ideal for several practical applications, particularly in the transport of both classical and quantum information. One could also wonder whether nature itself realized the usefulness of these unique entities and through evolution made living beings rely on them for some physiological functions. In my thesis, I cover an example for each of these roles a photon can take. As the first example, I describe our theoretical work pertaining to an important practical application where photons can carry quantum information and mediate entanglement between distant quantum computing nodes. We designed a novel quantum repeater architecture using superconducting processors and optical links, which we believe is the first concrete proposal towards this goal. We compared our repeater’s performance with a few other promising approaches and showed that ours could yield higher entanglement distribution rates with good fidelities in appropriate regimes. Such an architecture could be pertinent to envision a quantum internet in the future, something that would be analogous to, but much more secure and powerful in certain aspects than today’s classical internet. As the second example, I describe our theoretical work where we speculate on the potential role of photons observed in mammalian brains. Could we be using these photons as information carriers in addition to the well-known electrochemical signals? We show, based on detailed theoretical modelling, that myelinated axons could serve as good optical waveguides in the brain, which can answer this question in the affirmative. Ours is the first proposal identifying myelinated axons as potential optical waveguides. There is indirect experimental evidence to support this hypothesis, and we propose precise experiments to test the waveguide capabilities directly. Since these photons can also in principle carry quantum information, we further speculate on the existence of quantum networks in the brain. Our work could help develop a better understanding of some of the biggest unsolved problems in neuroscience, possibly including the generation of our subjective conscious experience.