Diamond photonics platform based on silicon vacancy centers in a single-crystal diamond membrane and a fiber cavity

We realize a potential platform for an efficient spin-photon interface, namely negatively-charged silicon-vacancy centers in a diamond membrane coupled to the mode of a fully-tunable, fiber-based, optical resonator. We demonstrate that introducing the thin ($\sim 200\text{nm}$), single crystal diamond membrane into the mode of the resonator does not change the cavity properties, which is one of the crucial points for an efficient spin-photon interface. In particular, we observe constantly high Finesse values of up to 3000 and a linear dispersion in the presence of the membrane. We observe cavity-coupled fluorescence from an ensemble of ${\mathrm{SiV}}^{-}$ centers with an enhancement factor of $\sim 1.9$. Furthermore from our investigations we extract the ensemble absorption and extrapolate an absorption cross section of $(2.9\pm 2)\times {10}^{-12}{\text{cm}}^2$ for a single ${\mathrm{SiV}}^{-}$ center, much higher than previously reported.

Figure 1

(a) Schematic sketch of the setup for the cavity measurements. The fiber mirror is mounted on a large damping block to reach high passive stability. We use a piezoelectric shear actuator to tune the cavity length. The flat mirror with the thin diamond membrane is mounted on a two-axis piezopositioning stage to allow lateral positioning. We use a $\text{NA}=0.7$ microscope air objective to excite color centers through the flat mirror and collect the outcoupled cavity mode. We analyze the cavity properties by measuring transmission of a $713\text{nm}$ laser with a photodiode and CCD camera. Fluorescence is measured with a single photon counting module (SPCM) and spectrometer. (b) Confocal image with red rectangle indicating the diamond membrane. The position of the ${\mathrm{SiV}}^{-}$ ensemble is marked as a green circle in the inset. (c) Photoluminescence (PL) spectrum of the ${\mathrm{SiV}}^{-}$ ensemble. A Lorentzian fit of the ZPL at $738\text{nm}$ yielding a FWHM linewidth of $8.83\text{nm}$.

Figure 2

Modification of cavity modes as a function of diamond layer thickness: (a)–(c) Simulation of resonance wavelengths for $t_d=(0.2,1,10)\mu \text{m}$ with an air layer between $t_a=0–5\mu \text{m}$ using equation (3). (d) Resonance wavelengths measured (dots) and theory (black curves) of the $0.2\mu \text{m}$ diamond membrane for $L=36–40\mu \text{m}$ cavities. (e) Theoretical distribution of the fundamental mode frequencies of a $10\mu \text{m}$ thick membrane for similar cavity lengths calculated using equation (3).

Figure 3

Extracting the Finesse of the setups: Measured cavity transmission as a function of the cavity length for an empty cavity (a) and with a $\approx 200\text{nm}$ thick diamond membrane inside the cavity (b). We normalized the intensities to the maximum transmitted intensity in the ${\mathrm{TEM}}_{00}$ mode, respectively. The corresponding Finesse values are ${\mathcal{F}}_e=2830$ for the empty cavity and ${\mathcal{F}}_d=2560$ for the diamond membrane cavity system.

Figure 4

(a) Cavity transmission measurement of the $713\text{nm}$ laser at the position of the ${\mathrm{SiV}}^{-}$ center ensemble resulting in a Finesse of ${\mathcal{F}}_{SiV}=401$. (b) PL spectrum of the ZPL of the ${\mathrm{SiV}}^{-}$ ensemble coupled to the cavity mode of a $L\approx 39\mu \text{m}$ cavity. Gaussian fits of the resonance peaks of the fundamental modes (red curves) yielding a linewidth of $264\text{GHz}$. Length jitter and absorption of the defect centers lead to broadening of the resonances. Coupling to higher order transverse modes leads to background and imperfect filtering of the cavity. (c) Mirrored PL spectrum of the ${\mathrm{SiV}}^{-}$ ensemble to illustrate expected absorption of the defect center. The inset shows a 2D confocal image of the ${\mathrm{SiV}}^{-}$ ensemble which has a lateral size (Gaussian FWHM) of $0.68\mu \text{m}$ ($0.64\mu \text{m}$). The red circle indicates the cavity mode waist for comparison.