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Excitation Dynamics

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Photosynthetic organisms fuel their energy needs by harvesting sunlight. Photosynthetic bacteria called purple bacteria live in the darkest places in ponds and lakes and as a result, every photon of sunlight that they receive must be efficiently collected and converted into chemical energy for the cell. Incoming photons are absorbed by proteins that contain many molecules of chlorophyll (see the October 2007 highlight on Life's Solar Battery). The chlorophylls capture light energy and transfer that energy between them. Such transfer, a quantum mechanical process, happens multiple times before the energy is converted to chemical energy and is governed by thermal interactions between chlorophylls and protein. A recent report showed that the surrounds thermalize, i.e., randomize, the light excitation migration within one picosecond (0.000000000001 second), after which the typically coherent quantum process looks incoherent. The finding explains the great success of earlier simpler descriptions suggested sixty years ago by the US physicist Robert Oppenheimer and German chemist Theodor Förster who postulated the now established incoherence. More here.