Figure 5. Optical linewidth and coherence properties of SiV.

(a) Cryogenic spectra (<18 K) of a single SiV (red circles) and an ensemble (black circles). The four SiV transitions (Fig. 1) as well as the phonon sideband are each fitted with a Gaussian function. The single SiV linewidths are spectrometer-limited (FWHM=∼34 GHz). For the ensemble, we determine an inhomogeneous broadening as low as ∼51 GHz (FWHM). The wavelength values are slightly blue-shifted because of an offset relative to an absolute wavelength reference by ∼0.1 nm. (b) Cryogenic (4 K) photoluminescence excitation measurement of the narrowest observed single SiV transition with a linewidth of 126±13 MHz (FWHM, error estimation: 95% confidence interval) determined with a Lorentzian fit function. This linewidth of an implanted SiV is equal, within error, to the narrowest natural SiV linewidth measured to date.