Vibronic Resonances Facilitate Excited-State Coherence in Light-Harvesting Proteins at Room Temperature
2015-12-17T10:46:41Z (GMT)
by
Until recently it was believed that
photosynthesis, a fundamental
process for life on earth, could be fully understood with semiclassical
models. However, puzzling quantum phenomena have been observed in
several photosynthetic pigment–protein complexes, prompting
questions regarding the nature and role of these effects. Recent attention
has focused on discrete vibrational modes that are resonant or quasi-resonant
with excitonic energy splittings and strongly coupled to these excitonic
states. Here we unambiguously identify excited state coherent superpositions
in photosynthetic light-harvesting complexes using a new experimental
approach. Decoherence on the time scale of the excited state lifetime
allows low energy (56 cm<sup>–1</sup>) oscillations on the
signal intensity to be observed. In conjunction with an appropriate
model, these oscillations provide clear and direct experimental evidence
that the persistent coherences observed originate from quantum superpositions
among vibronic excited states.