Ultralong coherence times in the purely electronic zero-phonon line emission of single molecules

We report the observation of ultralong coherence times in the purely electronic zero-phonon line emission of single terrylenediimide molecules at $1.4\mathrm{K}$ . Vibronic excitation and spectrally resolved detection with a scanning Fabry–Perot spectrum analyzer were used to measure a linewidth of $65\mathrm{MHz}$ . 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.