Two-electron-spin ratchets as a platform for microwave-free dynamic nuclear polarization of arbitrary material targets

TL;DR

This paper proposes a theoretical method using two-electron-spin ratchets in diamond to achieve microwave-free dynamic nuclear polarization of various materials at room temperature, overcoming orientation and defect-related challenges.

Contribution

It introduces a novel NV-P1 spin ratchet mechanism for efficient nuclear polarization transfer, robust to misalignments and relaxation effects, enabling ambient-condition polarization of arbitrary targets.

Findings

Efficient proton polarization via magnetic field sweep across NV-P1 anti-crossing.

Polarization sign depends on optical pulse timing.

Robust polarization transfer despite spin misalignment and relaxation.

Abstract

Optically-pumped color centers in semiconductor powders can potentially induce high levels of nuclear spin polarization in surrounding solids or fluids at or near ambient conditions, but complications stemming from the random orientation of the particles and the presence of unpolarized paramagnetic defects hinder the flow of polarization beyond the defect's host material. Here, we theoretically study the spin dynamics of interacting nitrogen-vacancy (NV) and 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. The process can be interpreted in terms of an NV-P1 spin ratchet, whose handedness - and hence the sign of the resulting nuclear polarization - depends on the relative timing of the optical excitation pulse. Further, we find that the polarization transfer mechanism is robust to NV misalignment relative to the external magnetic field, and efficient over a broad range of electron-electron and electron-nuclear spin couplings, even if proxy spins feature short coherence or spin-lattice relaxation times. Therefore, these results pave the route towards the dynamic nuclear polarization of arbitrary spin targets brought in proximity with a diamond powder under ambient conditions.