Photosynthetic proteins have evolved over billions of years so as to undergo optimal energy transfer to the sites of charge separation. On the basis of spectroscopically detected quantum coherences, it has been suggested that this energy transfer is partially wavelike. This conclusion depends critically on the assignment of the coherences to the evolution of excitonic superpositions. We demonstrate that, for a bacterial reaction center protein, long-lived coherent spectroscopic oscillations, which bear canonical signatures of excitonic superpositions, are essentially vibrational excited-state coherences shifted to the ground state of the chromophores. We show that the appearance of these coherences arises from a release of electronic energy during energy transfer. Our results establish how energy migrates on vibrationally hot chromophores in the reaction center, and they call for a reexamination of claims of quantum energy transfer in photosynthesis.

Department of Chemical Physics Charles University Ke Karlovu 3 CZ 121 16 Praha 2 Czech Republic

Department of Chemical Physics Lund University Box 124 SE 22100 Lund Sweden

Department of Chemistry and Molecular Biology University of Gothenburg Box 462 SE 40530 Gothenburg Sweden

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