Influence of photoexcitation conditions on the spin polarization of nitrogen-vacancy centers in isotopically enriched silicon carbide $6$H-$^{28}$SiC

Spin defects in semiconductors are attracting interest as a material basis for quantum information and computing technologies. In this work, the spin properties of negatively charged nitrogen-vacancy ($NV^{-}$) centers in a $6$H-SiC silicon carbide crystal enriched with the $^{28}$Si isotope were studied by high-frequency ($94$ GHz) electron paramagnetic resonance (EPR) methods. Due to an optical excitation channel at the $NV^{-}$ centers, it was possible to initialize the electron spin of the defect using a laser source, which led to a significant increase in the intensity of the recorded EPR signal. The dependences of the observed spin polarization were analyzed at different optical excitation wavelengths ($\lambda = 640$ – $1064$ nm), output power ($0$ – $500$ mW), and temperature ($50$ – $300$ K) of the crystal. The results obtained reveal the optimal experimental conditions for maximizing the efficiency of optical quantum energy transfer to the spin system. This opens up new possibilities for using $NV^{-}$ centers in $6$H-SiC to create multi-qubit spin-photon interfaces operating in the infrared region.