Recent observations of excitonic
coherences within photosynthetic complexes suggest that quantum coherences
could enhance biological light harvesting efficiencies. Here, we employ
optical pump–probe spectroscopy with few-femtosecond pulses
to observe an excitonic quantum coherence in CdSe nanocrystals, a
prototypical artificial light harvesting system. This coherence, which
encodes the high-speed migration of charge over nanometer length scales,
is also found to markedly alter the displacement amplitudes of phonons,
signaling dynamics in the non-Born–Oppenheimer regime