We report on the coupling of a single nitrogen-vacancy (NV) center in a nanodiamond to a fiber-based microcavity at room temperature. Investigating the very same NV center inside the cavity and in free space allows us to systematically explore a regime of phonon-assisted cavity feeding. Making use of the NV center's strongly broadened emission, we realize a widely tunable, narrow band single photon source. A master equation model well reproduces our experimental results and predicts a transition into a Purcell-enhanced emission regime at low temperatures.

Single photon sources are an integral part of various quantum technologies, and solid state quantum emitters at room temperature appear as a promising implementation. We couple the fluorescence of individual silicon vacancy centers in nanodiamonds to a tunable optical microcavity to demonstrate a single photon source with high efficiency, increased emission rate, and improved spectral purity compared to the intrinsic emitter properties. We use a fiber-based microcavity with a mode volume as small as 3.4 λ 3 and a quality factor of 1.9 × 10 4 and observe an effective Purcell factor of up to 9.2. We furthermore study modifications of the internal rate dynamics and propose a rate model that closely agrees with the measurements. We observe lifetime changes of up to 31%, limited by the finite quantum efficiency of the emitters studied here. With improved materials, our achieved parameters predict single photon rates beyond 1 GHz.

The silicon-vacancy (SiV) color center in diamond is a solid-state single photon emitter and spin quantum bit suited as a component in quantum devices. Here, we show that SiV centers in nanodiamonds exhibit a strongly inhomogeneous distribution with regard to the center wavelengths and linewidths of the zero-phonon-line (ZPL) emission at room temperature. We find that the SiV centers separate in two clusters: one group exhibits ZPLs with center wavelengths within a narrow range ≈730-742 nm and broad linewidths between 5 and 17 nm, whereas the second group comprises a very broad distribution of center wavelengths between 715 and 835 nm, but narrow linewidths from below 1 up to 4 nm. Supported by ab initio Kohn-Sham density functional theory calculations we show that the ZPL shifts of the first group are consistently explained by strain in the diamond lattice. Further, we suggest, that the second group showing the strongly inhomogeneous distribution of center wavelengths might be comprised of a new class of silicon-related defects. Whereas single photon emission is demonstrated for defect centers of both clusters, we show that emitters from different clusters show different spectroscopic features such as variations of the phonon sideband spectra and different blinking dynamics.

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In recent years, mono-layers and multi-layers of hexagonal boron nitride (hBN) have been demonstrated as host materials for localized atomic defects that can be used as emitters for ultra-bright, non-classical light. The origin of the emission, however, is still subject to debate. Based on measurements of photon statistics, lifetime and polarization on selected emitters we find that these atomic defects do not act as pure single photon emitters. Our results strongly and consistently indicate that each zero phonon line of individual emitters is comprised of two independent electronic transitions. These results give new insights into the nature of the observed emission and hint at a double defect nature of emitters in multi-layer hBN.