Electronic Structure of the Silicon Vacancy Color Center in Diamond

The negatively charged silicon vacancy (SiV) color center in diamond has recently proven its suitability for bright and stable single photon emission. However, its electronic structure so far has remained elusive. We here explore the electronic structure by exposing single SiV defects to a magnetic field where the Zeeman effect lifts the degeneracy of magnetic sublevels. The similar responses of single centers and a SiV ensemble in a low strain reference sample prove our ability to fabricate almost perfect single SiVs, revealing the true nature of the defect’s electronic properties. We model the electronic states using a group-theoretical approach yielding a good agreement with the experimental observations. Furthermore, the model correctly predicts polarization measurements on single SiV centers and explains recently discovered spin selective excitation of SiV defects.

Figure 1

Spectral fine structure of (a) an ensemble of ${\mathrm{SiV}}^{-}$ centers at 4 K and (c) single emitter SIL1 under a solid immersion lens at 18 K. The inset (b) shows the polarization of each single fine structure line. Black dots are measurements, red solid lines are simulations.

Figure 2

Spectral fine structure splitting of (a) a ${\mathrm{SiV}}^{-}$ ensemble (contour plot, color coding indicates peak intensity in logarithmic a.u.) and (b) single ${\mathrm{SiV}}^{-}$ defect under a SIL (SIL2) vs applied magnetic field [in the (001) direction]. White solid lines are calculated transitions based on the model mentioned in the text. The labeling of transitions is in accordance with Fig. 3. Panel (c) displays a simulation of the fine structure lines intensity assuming dipolar transitions.

Figure 3

Calculated splitting of electronic levels (with symmetry $E_g$, $E_u$) for zero magnetic field (a) and for increasing magnetic field (b). Ground and excited state labeled according to the letters and numbers at the right of the panel. Optical transitions between all levels indicated by black arrows and correspond to the white solid lines in Fig. 2. The expected polarizations in (a) reflect a simplified model neglecting JT interaction [14].

Figure 4

Tomography of the excited states at $B=4\mathrm{T}$ using the model parameters, which lead to the level splitting shown in Fig. 3. Basis states given in the eigenstates of the $L_{\mathrm{z}}$ operator $|e_{\pm }⟩=-(|e_{\mathrm{x}}⟩\pm i|e_{\mathrm{y}}⟩)$ and the $S_{\mathrm{z}}$ operator $|\uparrow ⟩$, $|\downarrow ⟩$.