Recently, several schemes centered around the negatively charged Nitrogen Vacancy(NV^-) color center in diamond as means to hyperpolarize nuclei have been realized^1–2. Here we theoretically consider the case of the NV and the substitutional nitrogen (P1) centers in diamond to show that outside protons spin-polarize efficiently upon a magnetic field sweep across the NV–P1 level anti-crossing. In particular, the nuclear polarization buildup during the low-to-high and high-to-low stages of the sweep cycle adds constructively regardless the relative sweep velocities. The system dynamics can be interpreted in terms of an NV–P1 spin ratchet whose sign depends on the relative timing of an accompanying optical excitation pulse. Our calculations indicate that the polarization transfer process is insensitive to the NV axis orientation, and efficient over a broad range of electron-electron and electron-nuclear spin couplings, even if the proxy spins suffers from short relaxation times.

1. Ajoy, A. et al. Orientation-independent room temperature optical13C hyperpolarization in powdered diamond. Sci. Adv. 4, 1–8 (2018).
2. Pagliero, D. et al. Multispin-Assisted optical pumping of bulk C 13 nuclear spin polarization in diamond. Phys. Rev. B 97, 024422 (2018).