Achieving 5 % $^{13}$C nuclear spin hyperpolarization in high-purity diamond at room temperature and low field

TL;DR

This study demonstrates a method to achieve 5% $^{13}$C nuclear spin hyperpolarization in high-purity diamond at room temperature and low magnetic fields, significantly enhancing nuclear spin polarization for potential quantum applications.

Contribution

The paper introduces a novel approach combining optimized magnetic field, MW sweep parameters, and diamond purity to attain high $^{13}$C polarization at room temperature and low field.

Findings

Achieved 5% $^{13}$C polarization at below 10 mT.

Long $^{13}$C spin storage time exceeding 100 minutes.

Polarization transfer primarily occurs via the integrated solid effect and spin diffusion.

Abstract

Optically polarizable nitrogen-vacancy (NV) center in diamond enables the hyperpolarization of $^{13}$C nuclear spins at low magnetic field and room temperature. However, achieving a high level of polarization comparable to conventional dynamic nuclear polarization has remained challenging. Here we demonstrate that, at below 10 mT, a $^{13}$C polarization of 5 % can be obtained, equivalent to an enhancement ratio over $7 \times 10^6$. We used high-purity diamond with a low initial nitrogen concentration ($<$ 1 ppm), which also results in a long storage time exceeding 100 minutes. By aligning the magnetic field along [100], the number of NV spins participating in polarization transfer increases fourfold. We conducted a comprehensive optimization of field intensity and microwave (MW) frequency-sweep parameters for this field orientation. The optimum MW sweep width suggests that polarization transfer occurs primarily to bulk $^{13}$C spins through the integrated solid effect followed by nuclear spin diffusion.