  Photosynthesis powers life on our planet. The basic photosynthetic
architecture comprises antenna complexes to harvest solar energy and reaction
centers to convert the energy into a stable charge separated state. In oxygenic
photosynthesis, the initial charge separation event occurs in the photosystem
II reaction center; the only known natural enzyme that uses solar energy to
split water. Energy transfer and charge separation in photosynthesis are rapid
and have high quantum efficiencies. Recently, nonlinear spectroscopic
experiments have suggested that electronic coherence may play a role in energy
transfer efficiency in antenna complexes. Here we report the observation of
coherence in the photosystem II reaction center by two dimensional electronic
spectroscopy. The frequencies of the observed coherences match exciton
difference frequencies and/or known vibrational modes of the photosystem II
reaction center. These observations raise questions about the possible role of
electronic and/or vibrational coherence in the fundamental charge separation
process in oxygenic photosynthesis.
