Non-reciprocal Light-harvesting Nanoantennae Made by Nature

Abstract: Most of our current understanding of mechanisms of photosynthesis comes from spectroscopy. However, classical definition of radio-antenna can be extended to optical regime to discuss the function of light-harvesting antennae. Further to our previously proposed model of a loop antenna we provide several more physical explanations on considering the non-reciprocal properties of the light harvesters of bacteria. We explained the function of the non-heme iron at the reaction center, and presented reasons for each module of the light harvester being composed of one carotenoid, two short $\alpha$-helical polypeptides and three bacteriochlorophylls; we explained also the toroidal shape of the light harvester, the upper bound of the characteristic length of the light harvester, the functional role played by the long-lasting spectrometric signal observed, and the photon anti-bunching observed. Based on these analyses, two mechanisms might be used by radiation-durable bacteria, {\it Deinococcus radiodurans}; and the non-reciprocity of an archaeon, {\it Haloquadratum walsbyi}, are analyzed. The physical lessons involved are useful for designing artificial light harvesters, optical sensors, wireless power chargers, passive super-Planckian heat radiators, photocatalytic hydrogen generators, and radiation protective cloaks. In particular it can predict what kind of particles should be used to separate sunlight into a photovoltaically and thermally useful range to enhance the efficiency of solar cells.