Microwave-free imaging magnetometry with nitrogen-vacancy centers in nanodiamonds at near-zero field

TL;DR

This work addresses the challenge of NV-based magnetometry requiring microwaves by demonstrating a microwave-free, near-zero-field imaging approach using NV centers in nanodiamonds. The authors exploit zero-field cross-relaxation to map magnetic fields with a wide-field setup, extracting center shift $\Delta B$, contrast $C$, and width $w$ of the zero-field feature via per-pixel Gaussian fits. They validate the method experimentally on a current-carrying cross-pattern, and corroborate the findings with Magpylib Biot–Savart simulations, achieving a per-pixel sensitivity of about $4.5~\mu T/\sqrt{Hz}$ and showing linear current dependence in relevant ranges. The results highlight the potential for microwave-free, all-optical wide-field magnetometry on nanodiamond coatings, enabling applications in biology and on irregular surfaces with real-time field imaging.

Abstract

Magnetometry using Nitrogen-Vacancy (NV) color centers in diamond predominantly relies on microwave spectroscopy. However, microwaves may hinder certain studies involving biological systems or thin conductive samples. This work demonstrates a wide-field, microwave-free imaging magnetometer utilizing NV centers in nanodiamonds by exploiting the cross-relaxation feature near zero magnetic fields under ambient conditions without applying microwaves. For this purpose, we measure the center shift, contrast, and linewidth of the zero-field cross-relaxation in 140 nm nanodiamonds drop-cast on a current-carrying conductive pattern while scanning a background magnetic field, achieving a sensitivity of 4.5 $\mathrm{μT/\sqrt{Hz}}$. Our work allows for applying the NV zero-field feature in nanodiamonds for magnetic field sensing in the zero and low-field regimes and highlights the potential for microwave-free all-optical wide-field magnetometry based on nanodiamonds.

Figures (5)

• Figure 1: (a) schematic of the wide-field magnetic imaging setup, (b) the conductive cross pattern embedded in a transparent substrate attached to a PCB with NDs deposited at the interjunction, (c) a single-shot microscopic fluorescence image of NV centers with the cross pattern in the background, (d) timing of the measurement and imaging protocol, (e) near-zero-field fluorescence spectra of the nanodiamonds.
• Figure 2: Maps of the shift $\Delta B$, contrast C, and width w of zero-field spectra for two current paths in the cross pattern with varying current intensities of 0 A, 0.3 A, and 0.5 A. (a)The current path is from point 3 to 4; (b) The current path is from point 1 to 4.The plots to the right of the maps are the single-pixel zero-field spectra extracted from the binned image data. The pixel locations are colored in the width maps.
• Figure 3: The first row shows maps of the center shift $\Delta B$, contrast C, and width w of the zero-field feature for I = 0.5 A. The second row shows the $z$ component of the magnetic field, contrast, and width as a function of distance from the cross for a specific row of pixels marked by a black horizontal line in the upper row images.
• Figure 4: Change in the Gaussian fit parameters as a function of applied current (shift and width correspond to the left scale, Contrast to the right scale).
• Figure 5: Numerical simulation of the B-field distribution at a distance of 0.11 mm from the surface of the cross pattern with an applied current of 0.5 A in two specific directions (a) path 3 to 4 and (b) path 1 to 4. The plots adjacent to the maps show the components of the B-field along the black line.