Photosynthetic light harvesting in vivo displays near unit quantum efficiency under ultra-weak illumination conditions. A new generation of experimental and theoretical studies using quantum light sources and coincidence counting now allows explicit study of the absorption of individual photons. First generation experiments reveal a cycle of single photon absorption and single photon fluorescent emission that validates the microscopic interpretation of conventional bulk measurements of quantum efficiency. I shall discuss how these techniques and related theoretical studies can probe the spatiotemporal dynamics of photosynthesis in a new and fundamental manner.
Using a photon-counting quantum light spectroscopy that probes photosynthetic light harvesting with a single photon at a time, we experimentally demonstrated that photosynthesis begins and proceeds with a single quantum of energy. We report the observation of individual single-photon absorption and emission events in spatially distinct regions in photosynthetic systems. The experiments were carried out on an ensemble of pigment-protein complexes light-harvesting 2 from purple bacteria Rhodobacter sphaeroides under ambient conditions in vitro.
We propose a metasurface-based shadow tomography protocol to measure the properties of quantum states efficiently. We design Si nano-disks based metagratings that act as efficient polarizing beam splitters and can distinguish orthogonal polarizations. This allows for the measurement of all necessary quantum state observables in parallel, reducing the time needed to characterize quantum states of photonic qubits and minimizes the impact of decoherence. We validate our protocol by performing numerical simulations of a two-qubit system with metasurface as quantum detectors. We show that the protocol can accurately estimate properties of quantum states with few measurements and without reconfiguring optical setups.
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