  We experimentally demonstrate high degree of polarization of 13C nuclear
spins weakly interacting with nitrogen-vacancy (NV) centers in diamond. We
combine coherent microwave excitation pulses with optical illumination to
provide controlled relaxation and achieve a polarity-tunable, fast nuclear
polarization of degree higher than 85% at room temperature for remote 13C
nuclear spins exhibiting hyperfine interaction strength with NV centers of the
order of 600 kHz. We show with the aid of numerical simulation that the
anisotropic hyperfine tensor components naturally provide a route to control
spin mixing parameter so that highly efficient nuclear polarization is enabled
through careful tuning of nuclear quantization axis by external magnetic field.
We further discuss spin dynamics and wide applicability of this method to
various target 13C nuclear spins around the NV center electron spin. The
proposed control method demonstrates an efficient and versatile route to
realize, for example, high-fidelity spin register initialization and quantum
metrology using nuclear spin resources in solids.
