Parallel accelerated electron paramagnetic resonance spectroscopy using diamond sensors

TL;DR

This paper introduces a zero-field, amplitude-modulated control technique for NV center-based EPR spectroscopy, enabling robust, efficient, and real-time measurements of free radicals using diamond sensors with large NV ensembles.

Contribution

It presents a novel cross-relaxation EPR method at zero field that overcomes inhomogeneity issues, improving sensitivity and enabling real-time radical monitoring.

Findings

Successful EPR spectra acquisition of free radicals.

Robust detection despite sensor and target inhomogeneities.

Real-time monitoring of radical dynamics.

Abstract

The nitrogen-vacancy (NV) center can serve as a magnetic sensor for electron paramagnetic resonance (EPR) measurements. Benefiting from its atomic size, the diamond chip can integrate a tremendous amount of NV centers to improve the magnetic-field sensitivity. However, EPR spectroscopy using NV ensembles is less efficient due to inhomogeneities in both sensors and targets. Spectral line broadening induced by ensemble averaging is even detrimental to spectroscopy. Here we show a kind of cross-relaxation EPR spectroscopy at zero field, where the sensor is tuned by an amplitude-modulated control field to match the target. The modulation makes detection robust to the sensor's inhomogeneity, while zero-field EPR is naturally robust to the target's inhomogeneity. We demonstrate an efficient EPR measurement on an ensemble of roughly 30000 NV centers. Our method shows the ability to not only acquire unambiguous EPR spectra of free radicals, but also monitor their spectroscopic dynamics in real time.