  We report the observation of ultralong coherence times in the purely
electronic zero-phonon line emission of single terrylenediimide molecules at
1.4 K. Vibronic excitation and spectrally resolved detection with a scanning
Fabry-Perot spectrum analyzer were used to measure a linewidth of 65 MHz. This
is within a factor of 1.6 of the transform limit. It therefore indicates that
single molecule emission may be suited for applications in linear optics
quantum computation. Additionally it is shown that high resolution spectra
taken with the spectrum analyzer allow for the investigation of fast spectral
dynamics in the emission of a single molecule.
