Cavity-Enhanced Single-Photon Source Based on the Silicon-Vacancy Center in Diamond

Single-photon sources are an integral part of various quantum technologies, and solid-state quantum emitters at room temperature appear to be 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 $3.4{\lambda }^3$ and a quality factor of $1.9\times 10^4$ and observe an effective Purcell factor of up to 9.2. Furthermore, we 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.

Figure 1

(a) Schematic of a cavity and a SiV center in diamond lattice (the vertical axis is in the [111] direction). (b) Interferometric measurement of fiber profile. (c) Cavity transmission spectra for different cavity lengths, starting at $d=5\lambda /2$ (the lowest curve), in steps of one free spectral range. Different resonance heights are due to the source spectrum and finite spectrometer resolution.

Figure 2

(a) Free-space fluorescence spectra of single SiV centers studied for cavity coupling. (b) Cavity fluorescence spectra of ND5 for different geometric cavity lengths (air gap), logarithmic color scale (cps: counts per second). (Top panel) Linear-scale spectrum for $d=0.875\mathrm{nm}$, where maximal enhancement occurs. (Left panel) Linear-scale plot of count rate for different lengths at the emission wavelength $\lambda =752.4\mathrm{nm}$.

Figure 3

(a) Lifetime measurement for ND3; data points and fit (the solid line) with an exponential function starting at $t=0$ convoluted with the system response function. Blue, free space; orange, cavity ($q=5$); green, cavity ($q=6$). (b) Cavity saturation measurement of ND4 (blue, data; red, fit).

Figure 4

(a) Free space $g^{(2)}$ measurement of ND1 using pulsed excitation (50-ps pulse duration, 20-MHz repetition rate, 690-nm wavelength). Red curve, data; blue histogram, integrated over each peak (background subtracted). (b) Free space $g^{(2)}$ measurement (cw excitation at 690 nm) of ND1 for selected excitation powers. (Inset) Enlargement of $0.17P_{\mathrm{sat}}$ data. Black solid lines, fit with $g^{(2)}$ function convoluted with system response function; orange solid line, $g^{(2)}$ function without convolution. (c) Fit parameters as a function of power and fit with power-dependent deshelving model (the solid lines). Dashed lines, fit with model from Ref. [34].

Figure 5

(a) Computed mirror transmission of (yellow) the fiber and (blue) the planar mirror. (b) Computed finesse assuming the above mirror transmissions and 40-ppm absorption losses.

Figure 6

(a) Confocal fluorescence map showing the count rate in megahertz. The marked spot is a narrow-line emitter. (b) Cavity transmission scan of the same area (with the transmission normalized to 1) for a cavity length of about $10\mu \mathrm{m}$. The marked spot is the same location as in (a).

Figure 7

(a) Free-space saturation measurement of ND4. Blue, data; red, fit. (b) Cavity measurement of ND4.

Figure 8

Correction factor for the Purcell factor attributable to the emitter’s position relative to the electric-field maximum. The red line represents the color center residing in the middle of a 100-nm large diamond. The shaded area indicates the uncertainty of the correction factor resulting from the unknown position of the emitter.

Figure 9

(a) Proposed level scheme. Green arrows represent constant rates. Red arrows indicate linearly power dependent rates. (b) Equivalent three-level system. The blue arrow shows a rate with a linear and constant term.

Figure 10

Fluorescence time trace (count rate on detector) of a single emitter featuring blinking.