  Spectral diffusion is the phenomenon of random jumps in the emission
wavelength of narrow lines. This phenomenon is a major hurdle for applications
of solid state quantum emitters like quantum dots, molecules or diamond defect
centers in an integrated quantum optical technology. Here, we provide further
insight into the underlying processes of spectral diffusion of the zero phonon
line of single nitrogen vacancy centers in nanodiamonds by using a novel method
based on photon correlation interferometry. The method works although the
spectral diffusion rate is several orders of magnitude higher than the photon
detection rate and thereby improves the time resolution of previous experiments
with nanodiamonds by six orders of magnitude. We study the dependency of the
spectral diffusion rate on the excitation power, temperature, and excitation
wavelength under off-resonant excitation. Our results suggest a strategy to
increase the number of spectrally indistinguishable photons emitted by diamond
nanocrystals.
