Direct evidence of quantum transport in photosynthetic light-harvesting complexes

• Published in: Proceedings of the National Academy of Sciences - PNAS 2011-12, Vol.108 (52), p.20908-20912
• Main Authors: Panitchayangkoon, Gitt, Voronine, Dmitri V, Abramavicius, Darius, Caram, Justin R, Lewis, Nicholas H. C, Mukamel, Shaul, Engel, Gregory S
• Format: Article
• Language: English
• Subjects: Antennas; Beat frequencies; Chlorobi - physiology; Chromophores; Electron spectroscopy; Electron transfer; Energy transfer; Energy Transfer - physiology; Excitons; Forced migration; light harvesting complex; Light-Harvesting Protein Complexes - physiology; Models, Chemical; Models, Molecular; Phase shift; Photosynthesis; Photosynthesis - genetics; Photosynthesis - physiology; Physical Sciences; Population dynamics; Proteins; Quantum Theory; Solar energy; Spectroscopy; Spectrum analysis; Spectrum Analysis - methods
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1105234108

The photosynthetic light-harvesting apparatus moves energy from absorbed photons to the reaction center with remarkable quantum efficiency. Recently, long-lived quantum coherence has been proposed to influence efficiency and robustness of photosynthetic energy transfer in light-harvesting antennae. The quantum aspect of these dynamics has generated great interest both because of the possibility for efficient long-range energy transfer and because biology is typically considered to operate entirely in the classical regime. Yet, experiments to date show only that coherence persists long enough that it can influence dynamics, but they have not directly shown that coherence does influence energy transfer. Here, we provide experimental evidence that interaction between the bacteriochlorophyll chromophores and the protein environment surrounding them not only prolongs quantum coherence, but also spawns reversible, oscillatory energy transfer among excited states. Using two-dimensional electronic spectroscopy, we observe oscillatory excited-state populations demonstrating that quantum transport of energy occurs in biological systems. The observed population oscillation suggests that these light-harvesting antennae trade energy reversibly between the protein and the chromophores. Resolving design principles evident in this biological antenna could provide inspiration for new solar energy applications.