Fig. 4. Hyperpolarization applications with NV centers in diamonds.

(A) Illustration of shallow NV polarization setup, where NV centers implanted ~3-nm-deep polarize-diffusing molecules in a solution outside of the diamond and (B) nanodiamonds with randomly oriented NV centers, where the polarization of ¹³C spins (orange) allows for the usage as MRI contrast agents. (C) Polarization transfer from near-surface NV centers to a bath of 1200 nuclear spin bath, using the same Rabi and Larmor frequency and sequence as in Fig. 2C averaged over NV centers with transition frequencies drawn from a Gaussian distribution with a (2π)20-MHz width. The simulation uses matrix product states (39) and a diffusion coefficient of D = 1.4/2.8 × 10⁻¹²m²/s (blue dotted/red dashed curve), resulting in different correlation times and efficiencies. The inset shows that the NV linewidth is well within the working range of the PulsePol protocol [Ω = (2π)50MHz]. More details of the simulation are included in the Supplementary Materials. (D) On the basis of the resilience to detunings |Δ| < (2π)30MHz for a Rabi frequency of Ω = (2π)50MHz, more than 11% of the NV orientations in nanodiamonds (azimuthal angle between 90° ± 6.5°, as shown on the sphere) contribute to polarization transfer.