  In this work, we demonstrate initialization and readout of nuclear spins via
a negatively charged silicon-vacancy (SiV) electron spin qubit. Under
Hartmann-Hahn conditions the electron spin polarization is coherently
transferred to the nuclear spin. The readout of the nuclear polarization is
observed via the fluorescence of the SiV. We also show that the coherence time
of the nuclear spin (6 ms) is limited by the electron spin-lattice relaxation
due to the hyperfine coupling to the electron spin. This work paves the way
towards realization of building blocks of quantum hardware with an efficient
spin-photon interface based on the SiV color center coupled to a long lasting
nuclear memory.
