We report high time-resolution measurements of photon statistics from pairs
of dye molecules coupled by fluorescence resonance energy transfer (FRET). In
addition to quantum-optical photon antibunching, we observe photon bunching on
a timescale of several nanoseconds. We show by numerical simulation that
configuration fluctuations in the coupled fluorophore system could account for
minor deviations of our data from predictions of basic Forster theory. With
further characterization we believe that FRET photon statistics could provide a
unique tool for studying DNA mechanics on timescales from 10^-9 to 10^-3 s.Comment: 4 pages, 4 figures, submitted to Physical Review Letter
