Miniaturized magnetic-field sensor based on nitrogen-vacancy centers

Phys. Rev. Appl. 24, 054078 (2025) · DOI: 10.1103/lbqj-d5zv · arXiv: 2402.19372

License: CC BY 4.0.

Abstract

The nitrogen-vacancy (NV) center in diamond is a prime candidate for quantum sensing technologies. Here, we present a fully integrated and mechanically robust fiber-based endoscopic sensor with a tip diameter of 1.25 mm. On its tip, a direct laser-writing process is used to secure a diamond containing NV centers above the fiber's core inside a polymer structure. Additionally, a metallic direct laser-written antenna structure next to the fiber facet allows efficient microwave manipulation of NV-center spins. The sensor achieves a shot-noise-limited magnetic-field sensitivity of 5.9 nT/√Hz using a 15-µm-sized microdiamond at a microwave power of 50 mW and an optical power of 2.15 mW. Using lock-in techniques, we measure a sensitivity of 51.8 nT/√Hz. Furthermore, we introduce a dual-fiber concept that enables, in combination with a direct laser-written structure, independent guiding of excitation and fluorescence light and thus reduces background autofluorescence. Moreover, controlled guiding of excitation light to the diamond while avoiding sample illumination may enable operation in light-sensitive environments such as biological tissue. While the demonstrated sensitivity is achieved using a single-fiber configuration, the dual-fiber approach provides a path toward integrating smaller diamonds, where autofluorescence would otherwise limit performance. We demonstrate the capability of vector magnetic-field measurements in the type of magnetic field used in state-of-the-art ultracold quantum gas experiments, opening a potential arena in which high resolution and high sensitivity are required.

Figures

12 panels with data across 7 figures. Each panel page shows the plot, its columns and its files; each data.csv begins with a header naming the paper, the panel, the source, the license and the provenance route.

Fig. 1

Illustrative figure, no extractable data. Shown in the paper PDF.

Fig. 2

Illustrative figure, no extractable data. Shown in the paper PDF.

Fig. 3

Illustrative figure, no extractable data. Shown in the paper PDF.

Fig. 4

Illustrative figure, no extractable data. Shown in the paper PDF.

Fig. 5

• panel (1): Left sub-plot of the printed figure: lock-in-amplified ODMR signal, LIA signal (arb. units) against MW frequency (MHz), with a bias magnetic field applied, and the fit of Lorentzian derivatives to the resonances. The right sub-plot, a zoom of the first resonance with its dashed zero-crossing slope, is not shown. data.csv

Fig. 6

• panel (1): Upper graph of the printed figure: ODMR spectrum, Fluorescence contrast against MW frequency (MHz), with excitation and detection through the multimode fiber, and the Lorentzian fit to the resonances. data.csv
• panel (2): Lower graph of the printed figure: ODMR spectrum, Fluorescence contrast against MW frequency (MHz), with excitation through the single-mode fiber and detection through the multimode fiber, and the Lorentzian fit to the resonances. data.csv

Fig. 7

• panel (a): Amplitude spectral noise density (nT/$\sqrt{\mathrm{Hz}}$) against Frequency (Hz), on log-log axes, for the magnetically sensitive, magnetically insensitive and electrical noise measurements. The dashed line marks the mean spectral noise density. The inset of the printed panel, a zoom of the magnetically sensitive trace, is not shown. data.csv
• panel (b): Overlapping Allan deviation (nT) against Integration time (s), on log-log axes. The shaded band is the uncertainty of each point, which the printed panel draws as error bars too small to be visible. The dashed $\tau^{-1/2}$ guide line of the printed panel is not drawn. data.csv

Fig. 8

• panel (1): Absolute $B$ field ($\mu$T) of the coils in anti-Helmholtz configuration as a colour map against $x$ and $y$ position (mm), with black arrows for the in-plane $B_x$ and $B_y$ components, each based at its measured position. As printed, all arrows have one length and show direction only. The map is drawn with equal axis scales, so it is square where the printed one is wider than tall. data.csv

Fig. 9

• panel (a): Measured and shot-noise-limited (SN lim.) sensitivity (T/$\sqrt{\mathrm{Hz}}$) against effective diamond size $l_{\mathrm{eff}}$ (mm), on log-log axes, for this work and other publications, each point labelled with its reference number as printed. The solid line is the volume-dependent shot-noise sensitivity. data.csv
• panel (b): Volume-normalized sensitivity ($\frac{\mathrm{T}}{\sqrt{\mathrm{Hz}}}\times\sqrt{\mathrm{mm}^3}$) against Laser power (mW), on log-log axes, measured and shot-noise-limited, for this work and other publications, each point labelled with its reference number as printed. data.csv

Fig. 10

Illustrative figure, no extractable data. Shown in the paper PDF.

Fig. 11

• panel (1): Left sub-plot of the printed figure: zero-crossing slope of the LIA output, LIA signal slope (arb. units), against MW modulation frequency, Mod. frequency (kHz), for all eight resonances, one curve each, named Resonance 1 to 8 in the drawn colour order. data.csv
• panel (2): Right sub-plot of the printed figure: zero-crossing slope of the LIA output, LIA signal slope (arb. units), against MW modulation deviation, Mod. deviation (MHz), for all eight resonances, one curve each, named Resonance 1 to 8 in the drawn colour order. data.csv

Fig. 12

• panel (a): Measured and shot-noise-limited (SN lim.) sensitivity (T/$\sqrt{\mathrm{Hz}}$) against effective sensing volume $l_{\mathrm{eff}}$ (mm), from the diamond or, if defined, the sensing volume, on log-log axes, each point labelled with its reference number as printed. The solid line is the volume-dependent shot-noise sensitivity. data.csv
• panel (b): Sensitivity normalized to the diamond or, if given, the sensing volume, Sens. vol. norm. sens. ($\frac{\mathrm{T}}{\sqrt{\mathrm{Hz}}}\times\sqrt{\mathrm{mm}^3}$), against Laser power (mW), on log-log axes, measured and shot-noise-limited, each point labelled with its reference number as printed. data.csv

Cite

Stefan Johansson, Dennis Lönard, Isabel Cardoso Barbosa, Jonas Gutsche, Jonas Witzenrath, Artur Widera. Miniaturized magnetic-field sensor based on nitrogen-vacancy centers. Phys. Rev. Appl. 24, 054078 (2025). https://doi.org/10.1103/lbqj-d5zv

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