  The nitrogen-vacancy (NV) centers (NCVSi) - in 4H silicon carbide (SiC)
constitute an ensemble of spin S = 1 solid state qubits interacting with the
surrounding 14N and 29Si nuclei. As quantum applications based on a
polarization transfer from the electron spin to the nuclei require the
knowledge of the electron-nuclear interaction parameters, we have used
high-frequency (94 GHz) electron-nuclear double resonance spectroscopy combined
with first-principles density functional theory to investigate the hyperfine
and nuclear quadrupole interactions of the basal and axial NV centers. We
observed that the four inequivalent NV configurations (hk, kh, hh, and kk)
exhibit different electron-nuclear interaction parameters, suggesting that each
NV center may act as a separate optically addressable qubit. Finally, we
rationalized the observed differences in terms of distinctions in the local
atomic structures of the NV configurations. Thus, our results provide the basic
knowledge for an extension of quantum protocols involving the 14N nuclear spin.
