Optical dynamic nuclear polarization of $^{13}$C spins in diamond at a low field with multi-tone microwave irradiation

TL;DR

This study demonstrates optical hyperpolarization of $^{13}$C nuclei in diamond at low magnetic fields and ambient temperature using multi-tone microwave irradiation, achieving significant polarization enhancement without cryogenics.

Contribution

It introduces a novel low-field, room-temperature DNP method utilizing multi-tone microwave irradiation to efficiently polarize $^{13}$C in diamond.

Findings

Achieved $^{13}$C polarization of 0.113% at low magnetic field.

Realized a polarization enhancement of approximately 90,000 times over thermal polarization.

Demonstrated the effectiveness of multi-tone microwave irradiation for DNP at ambient conditions.

Abstract

Most of dynamic nuclear polarization (DNP) has been requiring helium cryogenics and strong magnetic fields for a high degree of polarization. In this work, we instead demonstrate an optical hyperpolarization of naturally abundant $^{13}$C nuclei in a diamond crystal at a low magnetic field and an ambient temperature. It exploits continuous irradiations of pump laser for polarizing electron spins of nitrogen vacancy centers and microwave for transferring the induced polarization to $^{13}$C nuclear spins. Triplet structures corresponding to $^{14}$N hyperfine splitting were clearly observed in the spectrum of $^{13}$C polarization. The powers of microwave irradiation and pump laser were optimized. By simultaneously irradiating three microwave frequencies matching to the peaks of the triplet, we achieved a $^{13}$C bulk polarization of 0.113 %, leading to an enhancement of about a factor of 90,000 over the thermal polarization at 17.6 mT. We believe that the multi-tone irradiation can be universally adopted to further enhance the $^{13}$C polarization at a low magnetic field.