  We demonstrate coherent control of the optical transition of single
Nitrogen-Vacancy defect centers in diamond. On applying short resonant laser
pulses, we observe optical Rabi oscillations with a half-period as short as 1
nanosecond, an order of magnitude shorter than the spontaneous emission time.
By studying the decay of Rabi oscillations, we find that the decoherence is
dominated by laser-induced spectral jumps. By using a low-power probe pulse as
a detuning sensor and applying post-selection, we demonstrate that spectral
diffusion can be overcome in this system to generate coherent photons.
