Monday, July 1, 2013

1306.6650 (E. K. Irish et al.)

Vibration-assisted resonance in photosynthetic excitation energy

E. K. Irish, R. Gómez-Bombarelli, B. W. Lovett
Coherent quantum energy transfer, as observed in photosynthetic pigment-protein complexes, is inhibited by energetic disorder. While this difficulty can be overcome to some extent by the addition of environmental noise, it has recently has begun to be appreciated that discrete intra- and/or intermolecular vibrational modes may play an important role in quantum dynamics. We present a microscopic mechanism by which intramolecular vibrational modes create resonant energy transfer pathways, enhancing the efficiency of both coherent and dephasing-assisted transfer. The principles of this vibration-assisted resonance are illustrated in a simple model based on one energy-transfer branch of the well-characterised Fenna-Matthews-Olson complex. Despite its simplicity, this model captures the interplay between strong electronic coupling that produces delocalised exciton states and resonance-enhanced weak coupling to local vibrational modes. Analytical and numerical results show that intramolecular vibrations can enhance energy transport efficiency and suggest that the vibration-assisted resonance mechanism can overcome some of the limitations of dephasing-assisted transport.
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