Microwave-assisted cross-polarization of nuclear spin ensembles from optically-pumped nitrogen-vacancy centers in diamond

TL;DR

This paper demonstrates microwave-assisted cross-polarization transfer from NV centers in diamond to protons in a fluid, revealing insights into molecular diffusion near solid-liquid interfaces.

Contribution

It introduces a method for efficient polarization transfer from NV centers to external nuclear spins using microwave excitation, advancing hyperpolarization techniques.

Findings

Successful polarization transfer to protons in a viscous fluid

Observation of slower molecular diffusion near the diamond surface

Variable magnetic field and microwave conditions optimize transfer efficiency

Abstract

The ability to optically initialize the electronic spin of the nitrogen-vacancy (NV) center in diamond has long been considered a valuable resource to enhance the polarization of neighboring nuclei, but efficient polarization transfer to spin species outside the diamond crystal has proven challenging. Here we demonstrate variable-magnetic-field, microwave-enabled cross-polarization from the NV electronic spin to protons in a model viscous fluid in contact with the diamond surface. Slight changes in the cross-relaxation rate as a function of the wait time between successive repetitions of the transfer protocol suggest slower molecular diffusion near the diamond surface compared to that in bulk, an observation consistent with present models of the microscopic structure of a fluid close to a solid interface.