LAUSR

Significance We use ultrafast two-dimensional optical spectroscopy to study the primary steps in the energy transport in photosynthesis using the Fenna–Matthews–Olson complex as a model. By varying temperature to modify the intensity of decohering fluctuations, we determine the onset of quantum coherence effects at an ultralow temperature of 20 K. A theoretical analysis shows that this electronic quantum coherence can be separated from the pronounced vibrational coherences accompanying energy transport. We provide a complete picture of the lifetimes of electronic and vibrational quantum coherences and show that energy transport occurs under strong system–bath interactions. Electronic coherence can in principle sustain energy transfer at 20 K but rapidly fades away with increasing temperatures, becoming irrelevant under physiological conditions.