Dynamic Stabilization of the Optical Resonances of Single Nitrogen-Vacancy Centers in Diamond

We report electrical tuning by the Stark effect of the excited-state structure of single nitrogen-vacancy (NV) centers located $\lesssim 100\mathrm{nm}$ from the diamond surface. The zero-phonon line (ZPL) emission frequency is controllably varied over a range of 300 GHz. Using high-resolution emission spectroscopy, we observe electrical tuning of the strengths of both cycling and spin-altering transitions. Under resonant excitation, we apply dynamic feedback to stabilize the ZPL frequency. The transition is locked over several minutes and drifts of the peak position on timescales $\gtrsim 100\mathrm{ms}$ are reduced to a fraction of the single-scan linewidth, with standard deviation as low as 16 MHz (obtained for an NV in bulk, ultrapure diamond). These techniques should improve the entanglement success probability in quantum communications protocols.

Figure 1

(a) NV level structure at high transverse field ($d_{\perp }{F}_{\perp }\equiv {\delta }_{\perp }>15\mathrm{GHz}$). Dashed lines indicate the spin-selective decay path responsible for optical pumping. (b) Effect of longitudinal and (c) transverse electric fields on the excited state levels. (d) Fluorescence micrograph of the electrode structure. NV1 was illuminated by 532 nm light and appears white, while the position of NV2 is denoted with an asterisk. Metal electrodes appear as shadows.

Figure 2

(a) Stark emission spectroscopy. $V_a$ was slowly scanned ($1\mathrm{V}/\min$) and emission spectra were obtained in one-minute intervals. A dark exposure frame was taken every 8th frame (cyan vertical stripes). Emission frequencies are relative to 470.45 THz (637.25 nm). Low-field data are inset. (b) Emission spectrum for $V_a=1\mathrm{V}$ with expected peak positions labeled. The $|E_{x,y}⟩\to |0⟩$ emission line is fit with a Gaussian profile. (c) Low-field peak positions from (a) and global fit based on Eq. (1). Lorentzian fit uncertainty is smaller than the plotted symbols. (d) Total ZPL emission versus ${\delta }_{\perp }$. The emission rate was calculated by subtracting the mean background and summing counts over a range of $\sim 3$ FWHM linewidths centered at each peak. Error bars are based on Poissonian noise. (e) Relative intensity of the $|{\mathcal{E}}_y⟩\to |\pm 1⟩$ emission line along with fit (see text).

Figure 3

(a) PLE spectra versus applied voltage for NV1. A 532 nm repump pulse ($2.5\mu \mathrm{W}$, 1 s duration) was applied every 60 s. (b) Fitted transition frequencies from (a) and global fit based on Eq. (1), with transitions labeled. (c) PLE spectra for a single NV in the Ural sample ($|0⟩\to |E_x⟩$) at $V_a=-4\mathrm{V}$. Green arrows indicate when the repump was applied. (d) PLE spectra for the same NV with voltage feedback applied. (e) Fitted peak positions for scans in (c) [upper panel] and (d) [lower panel]. The recovery under feedback after two separate repump pulses are inset. (f) Histogram of the peak positions in (e). (g) 100 s segment of PLE spectra on NV2 obtained by rapidly scanning a voltage, $V_{\mathrm{ac}}$, with feedback applied to $V_{\mathrm{dc}}$.