NV金刚石传感器实现地磁场测量 OR μT级测量

In recent years, magnetic sensing based on the nitrogen-vacancy (NV) centers in diamonds has been considered to be a promising candidate for highly sensitive, spatial resolution solid-state quantum sensors. With the advancement of technology, scholars are committed to the introduction of miniaturized, highly integrated NV magnetometers. In this article, we integrate a focus system in the traditional laboratory into the sensor, propose a dual-focus magnetometer module (DFM), and design a signal-processing module (SPM) to perform current/voltage conversion–subtraction–amplification and filtering on the output signal of the DFM. Comparing the signal directly output by the DFM with the signal output after passing through the SPM the magnetic sensitivity and resolution are improved by 419 times and 256 times, respectively, and the magnetic resolution of the entire sensor reaches 24.6 nT in an area of 10.6 cm2. It has achieved a breakthrough in the resolution limit of integrated magnetometers in smaller volumes.

This paper provides a comprehensive review of quantum spin sensing with a focus on the nitrogen vacancy (NV) center in diamond. Beginning with the discovery of optically detected magnetic resonance in NV centers, we trace the evolution of this technology and its integration with complementary metal-oxide-semiconductor technology, marking a significant advancement in measurement science. The unique optical and spin properties of NV centers, operational at room temperature and under ambient conditions, have broadened their application spectrum, notably in magnetometry for nanoscale magnetic field detection. This work describes the transition from isolated NV centers to dense ensembles, highlighting the challenges and advancements in microfabrication and nanofabrication that have facilitated the integration of these centers with photonic structures and electronic devices. The efficient readout of NV spin states and the challenges in miniaturization are addressed, showcasing the development of compact, portable quantum sensors. We also discuss the potential impact of these sensors in various domains, including vehicle sensor systems and biomedical applications, underscoring the significance of environmental influences on magnetometric readings.

Quantum sensing based on NV-centers in diamonds has been demonstrated many times in multiple publications. The majority of publications use lasers in free space or lasers with fiber optics, expensive optical components such as dichroic mirrors, or beam splitters with dichroic filters and expensive detectors, such as Avalanche photodiodes or single photon detectors, overall, leading to custom and expensive setups. In order to provide an inexpensive NV-based magnetometer setup for educational use in schools, to teach the three topics, fluorescence, optically detected magnetic resonance, and Zeeman splitting, inexpensive, miniaturized, off-the-shelf components with high reliability have to be used. The cheaper such a setup, the more setups a school can afford. Hence, in this work, we investigated LEDs as light sources, considered different diamonds for our setup, tested different color filters, proposed an inexpensive microwave resonator, and used a cheap photodiode with an appropriate transimpedance amplifier as the basis for our quantum magnetometer. As a result, we identified cheap and functional components and present a setup and show that it can demonstrate the three topics mentioned at a hardware cost

… Diamond with negatively charged nitrogen-vacancy (NV – ) colour centers is a … for magnetometry. The sensing protocol leverages on optically detected magnetic resonance (ODMR) …

… The parameters of their ODMR spectra were analyzed and compared with those of treated … the NV – centers indicating the lower stress level in the crystals. We also found that the ODMR …

… ODMR technique was used for detecting the magnetic field. The sensitivity, η, of the cw ODMR based magnetometer … Ma et al., Portable diamond NV magnetometer head integrated with …

In recent years, there has been significant progress in the development of quantum precision measurement techniques. One particularly promising application is the use of the magnetometer based on diamond nitrogen vacancy (NV). However, to make this magnetometer more practical and flexible, it must be considered to avoid all the large instrumentation it involves and ensure a good magnetic sensitivity. In this article, we propose a high-precision portable application magnetometer (HPAM) that integrates all the equipment in the optical detection of magnetic resonance (ODMR) and limits the overall volume to about 190 cm3. We have also used a signal conditioning module (SCM) to process the fluorescence signal and enhance the sensitivity of the system. In addition, we separate the optical probe part from the back-end circuit part to well avoid interference between them; in the back-end part, we use 4G wireless data transmission and are equipped with a global positioning system (GPS) for remote magnetometry, which is a guideline for future practical integration design. Finally, we verified that the magnetic sensitivity of the system is about 4.22 nT/Hz $^{{1}/{2}}$ at 100 Hz and the total power consumption is 2.225 W. This new sensing system integrates all devices and has a good magnetic sensitivity.

Nitrogen vacancy (NV) center magnetometers offer theoretical advantages such as high sensitivity, wide dynamic range, and vector capability; however, achieving all these performance metrics simultaneously in a single device remains a significant challenge. Our study presents an NV-based vector magnetometry system optimized for high-sensitivity, wide-range magnetic field measurements to overcome this issue. Our approach utilizes a frequency-locking technique combined with frequency hopping, enabling robust tracking of resonance frequencies over a wide magnetic field range via a high-speed direct digital synthesizer. We achieve real-time vector field reconstruction with high temporal resolution by continuously monitoring the resonance frequency. The proposed system demonstrates significant improvements in dynamic range, sensitivity, and tracking speed, positioning it as an essential tool for a variety of quantum sensing applications.

Heteroepitaxial chemical vapor deposition is the most promising option to fabricate wafer-scale monocrystalline diamonds for quantum applications. Previously, we demonstrated the feasibility to manufacture functional micrometer-sized pyramids on as-grown heteroepitaxial diamond as well as their quantum optical characteristics. Due to high background signals and microfabrication challenges, these pyramids could not compete with homoepitaxially grown structures. In this study, we overcame these problems with a nominally undoped buffer layer between the heteroepitaxial substrate and the pyramidal microstructure to reduce the signal-to-noise ratio from the substrate on the spin measurements of the nitrogen-vacancy (NV) center. Moreover, the microfabrication was improved to reach a higher angle of the pyramidal side plane, corresponding to the {111} facets. These improvements lead to pyramids on which each facet contains almost purely only one of the four possible NV orientations as shown by optically detected magnetic resonance (ODMR). ODMR shows a very high contrast of 19% without an external magnet and of 13% for a single spin resonance in the presence of a magnetic field. The contrast is more than doubled compared to our previous study. The T2* dephasing time of the NV centers of the samples ranges from 0.02 to 0.16 μs. The P1 center is a single substitutional nitrogen center, and the P1 densities range from 1.8 to 5 ppm.

… , the ODMR signal … NV axes are degenerate, and the ODMR signal shows only one splitting in figurer 4b. When the magnetic field is not aligned with the crystallographic axis or an NV …

Integration of NV−-rich diamond with optical fibers enables guiding quantum information on the spin state of the NV− color center. Diamond-functionalized optical fiber sensors have been demonstrated with impressive sub-nanotesla magnetic field sensitivities over localized magnetic field sources, but their potential for distributed sensing remains unexplored. The volumetric incorporation of diamonds into the optical fiber core allows developing fibers sensitive to the magnetic field over their entire length. Theoretically, this makes distributed optical readout of small magnetic fields possible, but does not answer questions on the addressing of the spatial coordinate, i.e., the location of the field source, nor on the performance of a sensor where the NV− fluorescence is detected at one end, thereby integrating over color centers experiencing different field strength and microwave perturbation. Here, we demonstrate distributed magnetic field measurements using a step-index fiber with the optical core volumetrically functionalized with NV− diamonds. A microwave antenna on a translation stage is scanned along a 13 cm long section of a straight fiber. The NV− fluorescence is collected at the fiber's far end relative to the laser pump input end. Optically detected magnetic resonance spectra were recorded at the fiber output for every step of the antenna travel, revealing the magnetic field evolution along the fiber and indicating the magnetic field source location. The longitudinal distribution of the magnetic field along the fiber is detected with high accuracy. The simplicity of the demonstrated sensor would be useful for, e.g., magnetic-field mapping of photonics- and/or spintronics-based integrated circuits.

… magnetometers include fluxgate magnetometers, proton precession magnetometers, optically pumped magnetometers… wave (cw) ODMR studies on single or ensemble NV – centers at …

The nitrogen-vacancy (NV) center in diamond has become a widely used platform for quantum sensing. The four NV axes in monocrystalline diamond specifically allow for vector magnetometry, with magnetic-field sensitivities reaching down to <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>fT</a:mi> <a:mo>/</a:mo> <a:msqrt> <a:mi>Hz</a:mi> </a:msqrt> </a:mrow> </a:math> . The current literature primarily focuses on improving the precision of NV-based magnetometers. Here, we study the experimental accuracy of determining the magnetic field from measured spin-resonance frequencies via solving the NV Hamiltonian. We derive exact, analytical, and fast-to-compute formulas for calculating resonance frequencies from a known magnetic-field vector, and vice versa (formulas for calculating the magnetic-field vector from measured resonance frequencies). Additionally, the accuracy of often-used approximations is assessed. Finally, we promote using the Voigt profile as a fit model to determine the linewidth of measured resonances accurately. An open-source Python package accompanies our analysis.

Magnetometers based on nitrogen-vacancy (NV) centers in diamonds have promising applications in fields of living systems biology, condensed matter physics, and industry. This paper proposes a portable and flexible all-fiber NV center vector magnetometer by using fibers to substitute all conventional spatial optical elements, realizing laser excitation and fluorescence collection of micro-diamond with multi-mode fibers simultaneously and efficiently. An optical model is established to investigate multi-mode fiber interrogation of micro-diamond to estimate the optical performance of NV center system. A new analysis method is proposed to extract the magnitude and direction of the magnetic field, combining the morphology of the micro-diamond, thus realizing μm-scale vector magnetic field detection at the tip of the fiber probe. Experimental testing shows our fabricated magnetometer has a sensitivity of 0.73 nT/Hz1/2, demonstrating its feasibility and performance in comparison with conventional confocal NV center magnetometers. This research presents a robust and compact magnetic endoscopy and remote-magnetic measurement approach, which will substantially promote the practical application of magnetometers based on NV centers.

Nitrogen vacancy (NV) centers in diamond exhibit the advantages of high resolution, high sensitivity, and error-free sensing in the field of vector field detection, which bolsters the potential of NV center magnetometers for practical applications. However, most of the NV center magnetometers are still limited by the constraints imposed by bulky laboratory instruments, and the method of sweeping frequency points to detect resonance frequencies can also lead to slower detection of vector magnetic fields (MF). To address these limitations and enhance the portability of integrated vector magnetometers, we made an integrated vector magnetometer based on NV centers and proposed a microwave (MW) frequency-hopping method to realize vector MF triaxial real-time (400 ms) detection. The experimental results indicate that the magnetometer dynamic range is <inline-formula> <tex-math notation="LaTeX">$\pm 130 ~\mu \text{T}$ </tex-math></inline-formula> along the x-axis, <inline-formula> <tex-math notation="LaTeX">$\pm 110 ~\mu \text{T}$ </tex-math></inline-formula> along the y-axis, and <inline-formula> <tex-math notation="LaTeX">$\pm 260 ~\mu \text{T}$ </tex-math></inline-formula> along the z-axis, with the minimum standard deviation of vector MF measurements across all three axes being 1.84 nT. The frequency-hopping method is more than 87 times faster than the sweeping method and the size of the integrated NV magnetometer fits in the palm of the hand for portable usage. This proposal, which accomplishes vector MF rapidly measure using a self-made NV centers magnetometer, has potential applications in fields such as medical diagnosis, new energy battery testing, and geomagnetic detection.

… of the vector magnetometry based on nitrogen-vacancy (NV) … Here, we demonstrate a method of vector magnetometry in … reconstructed the magnetic field vector. The minimum magnetic …

… Negatively charged nitrogen-vacancy (NV − ) centers in diamond enable precise vector … However, noise is often direction-dependent and non-stationary during the vector measurement …

… , and can push forward the development for nitrogen-vacancy magnetometer in … the vector magnetic field sensing such as the nitrogen-vacancy (NV) center ensembles magnetometer [5]…

Nitrogen-vacancy (NV) centers in diamond are extremely promising solid-state spin quantum sensors for magnetic field in recent years. The rapid development of NV-ensemble magnetometry has put forward higher requirements for high-speed data acquisition, real-time signal processing and analyzing, etc. However, the existing commercial instruments are bulky and expensive, which brings extra complexity to the weak magnetic field detection experiment and hinders the practicality and miniaturization of NV-ensemble magnetometry. Here, we report on an integrated and scalable experimental system based on a field-programmable-gate-array (FPGA) chip assisted with high-speed peripherals for NV-ensemble magnetometry, which presents a compact and compatible design containing high-speed data acquisition, oscilloscopes, signal generator, spectrum analyzer, lock-in amplifier, proportional-integral-derivative feedback controller, etc. To verify its applicability and reliability in experiments, various applications, such as optical magnetic resonance detection, optical cavity locking, and lock-in NV magnetometry, are conducted. We further realize the pump-enhanced magnetometry based on NV center ensembles using the optical cavity. Through the flexible FPGA design approach, this self-developed device can also be conveniently extended into atomic magnetometer and other quantum systems.

Quantum sensing with solid-state spins offers the promise of high spatial resolution, bandwidth, and dynamic range at sensitivities comparable to more mature quantum sensing technologies, such as atomic vapor cells and superconducting devices. However, despite comparable theoretical sensitivity limits, the performance of bulk solid-state quantum sensors has so far lagged behind these more mature alternatives. A recent review~\cite{barry2020sensitivity} suggests several paths to improve performance of magnetometers employing nitrogen-vacancy defects in diamond, the most-studied solid-state quantum sensing platform. Implementing several suggested techniques, we demonstrate the most sensitive nitrogen-vacancy-based bulk magnetometer reported to date. Our approach combines tailored diamond growth to achieve low strain and long intrinsic dephasing times, the use of double-quantum Ramsey and Hahn echo magnetometry sequences for broadband and narrowband magnetometry respectively, and P1 driving to further extend dephasing time. Notably, the device does not include a flux concentrator, preserving the fixed response of the NVs to magnetic field. The magnetometer realizes a broadband \textcolor{mhsnew}{near-}DC sensitivity $\sim 460$~fT$\cdot$s$^{1/2}$ and a narrowband AC sensitivity $\sim 210$~fT$\cdot$s$^{1/2}$. We describe the experimental setup in detail and highlight potential paths for future improvement.

In this paper, we present a real-time vector magnetic field tracking method based on nitrogen vacancy (NV) centers magnetic detection technique. By combining optical detection magnetic resonance (ODMR) spectroscopy with multi-channel microwave frequency modulation (FM) technology, magnetic field information for each NV axis is extracted from the fluorescence signals captured by a single photodetector (PD), followed by real-time demodulation. The real-time vector magnetic field tracking method is more than 28 times faster than the frequency hopping method. Subsequently, multi-channel feedback control is introduced to track the resonance frequency of each NV axis in real-time, enabling real-time vector tracking measurements. The experimental results show that the dynamic range of the AC magnetic field is ±148.8 µT for the X, ± 151.2 µT for the Y, and ±152.5 µT for the Z. The sensitivities are 0.93nT/Hz, 0.76nT/Hz, 0.54nT/Hz respectively, which further validated the feasibility of the method. The method has potential applications in space exploration, medical diagnosis, navigation and other fields.

… We demonstrate a scalar magnetometry system capable of wide-range measurement from 2 … field resolution, vector measurement capability and so on. The nitrogen-vacancy (NV) …

The practical applications require the nitrogen-vacancy (NV) magnetometer to be transportable and highly sensitive. In this study, we have demonstrated a portable NV magnetometer consisting of a sensor head and miniaturized control system with a volume of <inline-formula> <tex-math notation="LaTeX">$22\times 19\times 12$ </tex-math></inline-formula> cm, which can operate outside the laboratory when connected to a computer. The sensor exhibited a sensitivity of 892.7 pT/Hz<inline-formula> <tex-math notation="LaTeX">$^{\text {1/2}}$ </tex-math></inline-formula>, achieved through the use of a fluorescence omni-directional reflection concentrator (FORC) and common mode laser noise rejection (CMR) technology. Notably, the FORC increased the fluorescence collection efficiency to 57% by allowing the collection of fluorescence emitted from all six facets of the diamond. Our work is expected to facilitate the transition of NV magnetometers from a laboratory platform to practical applications.

A customized control and readout device, which is developed to perform real-time measurement for vector magnetometers based on nitrogen-vacancy centers, is presented in this paper. A dual-channel analog-to-digital-converter chip, which has a 25 MSa/s sampling rate and a 16 bits amplitude resolution, is integrated for analog signal acquisition. The data processing and the system control are realized using a Xilinx Kirtex-7 field-programmable-gate-array chip. Eight independent lock-in modules, a four-channel proportional-integral-derivative controller, a reference generator, and a vector field reconstruction module are integrated with the Kirtex-7 device in order to perform the real-time vector magnetic field measurement. The device has a bright future to be applied in practical applications.

Since the introduction of Hall magnetometers, different types of magnetometers have been widely used. Among them, magnetometers based on nitrogen-vacancy (NV) centers in diamonds are promising room-temperature solid-state sensors. Their sensitivity to low-frequency (< 10 Hz) magnetic fields has been reported to be currently at the nanotesla level. Still, limitations in the detectable spatial range hinder their potential applications in medical imaging, earth sciences, and navigation. The most recent sensitivity enhancement technique involves using high-permeability flux concentrators with a unique magnetic field amplification structure that can cause the NV magnetometer to lose its vector detection capabilities. To address this limitation, we proposed a hybrid magnetometer based on a diamond-based hetero-NV center, which collects magnetic flux over a larger area and concentrates it in the diamond magnetometer, from which the magnetic field vector can be calculated by measuring the specific magnetic field direction vector. The low-frequency sensitivity of 90 pT $\cdot $ Hz $^{{(!{-}!){1}/{2}}}$ under conventional ambient conditions has been solved by inserting NV-doped diamond blocks between four permalloy concentrators in a triangular structure, which solves the vector deficiency problem of traditional magnetic concentrators. High-sensitivity real-time variation acquisition of the magnetic field signal has been achieved by applying an ac magnetic field in combination with modulation and demodulation methods.

Nitrogen-vacancy (NV) ensembles are viable magnetometers to be implemented on nanosatellites for monitoring geomagnetic fluctuations, which are credible precursors for predicting earthquakes at short notice. In this work, a Haar wavelet-based quantum sensing method is proposed to reconstruct the time-varying waveform of geomagnetic fluctuations in the very low frequency band. To collect different frequency components of fluctuations waveform at once, we propose a schematic to employ multiple NV ensembles (NVEs), with each controlled by an independent microwave source. Berry sequences are applied on one set of NVEs to extract the scaling coefficients from accumulated geometric phases to reconstruct near-dc components of a waveform. Spin-echo sequences are applied to another set of NVEs to extract the Haar wavelet coefficients from the dynamic phases to reconstruct high-frequency components. The efficacy of the proposed sensing protocol implemented on multiple NVEs is validated by reconstructing a waveform of geomagnetic fluctuations from a DEMETER satellite dataset through simulations. Each NVE is assumed to contain <inline-formula><tex-math notation="LaTeX">$N = 10^{8}$</tex-math></inline-formula> uncorrelated NV centers. The application of a Berry sequence to each NVE can achieve the maximum detectable magnetic field of over <inline-formula><tex-math notation="LaTeX">$460 \ \mu$</tex-math></inline-formula>T, resolving the issues of phase ambiguity and hyperfine-induced detuning if conventional Ramsey sequence were applied. The feasibility of the proposed simulation scenario considering spin-bath noise within an NVE is justified by simulations. The effects of wavelet scales, Rabi frequency in Berry sequence, and number of NV centers in each NVE are analyzed. The proposed NVE quantum sensors operated with the proposed sensing protocol can be installed on nanosatellites to monitor global geomagnetic fluctuations, with sub-<inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>s temporal resolution in the near future.

Diamond nitrogen vacancy (NV) color centers have high spatial resolution and long decoherence times at room temperature. Diamond NV magnetometer shows good application prospects as a quantum magnetometer field. In order to solve the problem of mobility regarding the larger and complex system equipment of diamond magnetometer, it is becoming increasingly important that each device in the diamond magnetometer system be miniaturized and integrated. In this article, we demonstrate a portable and highly integrated diamond magnetometer module (PHIDMM). The PHIDMM consists of a pump source and a magnetometer sensitive probe. The pump source consists of a stable laser diode with its heat sink and a focusing lens. Diamond sample, microwave antenna printed circuit plates (PCB), filters, photodetector (PD) and PD PCB, and other necessary fixed components are integrated together as diamond magnetometer sensitive probe. Magnetic flux concentrators (MFCs) are also integrated in the sensitive probe, which are used to gather flux in a small space and to enhance the sensitivity of the diamond magnetometer. Through actual tests and calculations, the magnetic field gain is increased by a factor of 17.02 with the assembly of MFCs. The portable and highly integrated magnetometer equipped with MFCs has a sensitivity of 0.54 nT/Hz $^{1/2}$ . The volume of the sensitive probe in the portable and highly integrated module is 8.8 cm3. In the designed PHIDMM, each component can be easily assembled together and the overall manufacturing cost is low, which provides new ideas for the industrial mass production of diamond magnetometers and the research of fully portable diamond magnetometers.

The nitrogen-vacancy (NV) centers ensemble has extensive application prospects in vector-magnetic-field measurement due to its accurate and fixed spatial orientations along the crystallographic axes of diamonds. However, to address signals of NV centers along all four axes, a large bias magnetic field sufficient to spectrally separate their resonances is typically inevitable, which may affect the magnetic substance under test and require multiple-frequency microwaves to interrogate signals of the four axes. Here, we demonstrate an NV-based simultaneous vector magnetometer that works at a bias field as low as just separating the resonant peaks of |ms=±1 states and utilizes a single-frequency microwave. By simultaneously detecting the fluorescence at specific optical polarization angles in three orthogonal directions and determining the transformation matrix in advance, all the Cartesian components of the magnetic field under test are distinguished. The experimentally achieved magnetic-field sensitivity is 63 nT/Hz, and the bias field is reduced to around 11 Gauss (still reducible by narrowing the linewidth) in ambient conditions. The proposed methods dramatically reduce the bias field for NV-based simultaneous vector magnetometers and potentially expand their applications in biological science, materials science, and industrial noninvasive detection.

… sensor that leverages NV centers for simultaneous sensing … in NV centers aligned along the four tetrahedral diamond axes. … the diurnal variations in geomagnetic field. This device marks …

Vector magnetometers provide lots of information for applications that require analysis of magnetic source ranging from bio-imaging to geophysical exploration. Magnetometer based on nitrogen-vacancy (NV) centers in diamond, as an unprecedented combination of spatial resolution and magnetic sensitivity, however, normally needs complex manipulation to distinguish the correspondence between field projections and NV axes, or is even unable to measure certain field directions. We developed an omnidirectional vector magnetometry that is not only intelligent and convenient, but also capable of measuring dead zones due to overlapping. With a conventional laboratory setup and commercial NV samples, we achieved an angular resolution around 0.02° in all direction of magnetic field and an angular error around 0.2°. The angular resolution is expected to reach arc seconds by optimization of experimental conditions. This method can improve the universality and practicality of NV magnetometers, and promote the development of NV toward industrial magnetometers.

… sensing technology based on diamond nitrogen vacancy (NV) centers has attracted the … based on diamond nitrogen vacancy centers, which integrates optical fiber, diamond, microwave …

Nitrogen-vacancy (NV) centers in diamonds are promising solid-state magnetic sensors with potential applications in power systems, geomagnetic navigation, and diamond NV color center current transformers, in which both high bandwidth and high magnetic field resolution are required. The wide bandwidth requirement often necessitates high laser power, but this induces significant laser fluctuation noise that affects the detection magnetic field resolution severely. Therefore, enhancement of the magnetic field resolution of wide-bandwidth NV center magnetic sensors is highly important because of the reciprocal effects of the bandwidth and magnetic field resolution. In this article, we develop a common mode rejection (CMR) model to eliminate the laser noise effectively. The simulation results show that the noise level of the light-detected magnetic resonance signal is significantly reduced by a factor of 6.2 after applying the CMR technique. After optimization of the laser power and modulation frequency parameters, the optimal system bandwidth was found to be 75 Hz. Simultaneously, the system’s detection magnetic field resolution was enhanced significantly, increasing from 4.49 nT/Hz1/2 to 790.8 pT/Hz1/2, which represents an improvement of nearly 5.7 times. This wide-bandwidth, high-magnetic field resolution NV color center magnetic sensor will have applications including power systems, geomagnetic navigation, and diamond NV color center current transformers.

High-dynamic-range integrated magnetometers demonstrate extensive potential applications in fields involving complex and changing magnetic fields. Among them, Diamond Nitrogen Vacancy Color Core Magnetometer has outstanding performance in wide-range and high-precision magnetic field measurement based on its inherent high spatial resolution, high sensitivity and other characteristics. Therefore, an innovative frequency-tracking scheme is proposed in this study, which continuously monitors the resonant frequency shift of the NV color center induced by a time-varying magnetic field and feeds it back to the microwave source. This scheme successfully expands the dynamic range to 6.4 mT, approximately 34 times the intrinsic dynamic range of the diamond nitrogen-vacancy (NV) center. Additionally, it achieves efficient detection of rapidly changing magnetic field signals at a rate of 0.038 T/s.

… a geomagnetic field environment reveal a measured standard deviation of 0.1 µT, which is 0.2% relative to the geomagnetic … structure of diamond provides NV center ensembles with …

… Diamond Nitrogen vacancy (NV) color center-based weak … The primary method of NV color center magnetic field measurement is the … At last, a diamond NV color center magnetometer is …

… which is reflected by the fluorescence of the N-V centers and can be detected through the optically detected magnetic resonance (ODMR) technique. The measurement strategy …

… provided magnetic field gradient measurement with a 35 mT dynamic range without the presence of microwaves. Specific applications, like the control of magnetic switching in …

… the ND ensemble enable detection of magnetic fields with arbitrary … ODMR with SP-STM by developing an STM stage equipped with a coplanar waveguide, enabling reliable microwave …

Integrated and fiber-packaged magnetic field sensors with a sensitivity sufficient to sense electric pulses propagating along nerves and a spatial resolution fine enough to resolve their propagation directions will trigger tremendous steps ahead in medical diagnostics and research. Nitrogen-vacancy centers in diamond are best suitable for such sensing tasks under ambient conditions. Current research on uniting a good sensitivity and high spatial resolution is facilitated by scanning or imaging techniques. However, these techniques employ moving parts or bulky microscopes. Both approaches cannot be miniaturized to build robust, adjustment-free, hand-held devices. In this work, we introduce concepts for spatially resolved magnetic field sensing and two-dimensional gradiometry with an integrated magnetic field camera. The camera utilizes infrared absorption optically detected magnetic resonance (IRA ODMR) mediated by perpendicularly intersecting infrared and pump laser beams forming a pixel matrix. We demonstrate our scalable 3×3 pixel sensor’s capability to reconstruct the position of an electromagnet. In a reference measurement, we show an IRA ODMR sensitivity of 44nTHz−1/2. Published by the American Physical Society 2025

Nitrogen vacancy (NV) centers in diamonds have been explored for a wide range of sensing applications in the last decade due to their unique quantum properties. In this work, we report a compact and portable magnetometer with an ensemble of NV centers, which we call the Quantum MagPI (Quantum Magnetometer with Proportional Integral control). Our fully integrated compact sensor assembly and control electronics fit inside a 10 × 10 × 7 cm3 box and a 30 × 25 × 5 cm3 rack-mountable box, respectively. We achieve a bandwidth normalized sensitivity of ∼10 nT/Hz. Using closed-loop feedback for locking to the resonance frequency, we extend the linear dynamic range to 200 μT (20× improvement compared to the intrinsic dynamic range) without compromising the sensitivity. We report a detailed performance analysis of the magnetometer through measurements of noise spectra, Allan deviation, and tracking of nT-level magnetic fields in real-time. In addition, we demonstrate the utility of such a magnetometer by real-time tracking of the movement of an elevator car and door opening events by measuring the projection of the magnetic field along one of the NV-axes under ambient temperature and humidity conditions.

Nitrogen-vacancy (NV) centers in diamond have become a powerful tool for wide-field magnetic field imaging. However, the conventional magnetic field imaging system based on NV centers relies on experimental platforms and is not mobile, resulting in limited working scenarios. In this article, we have designed a portable magnetic camera (PMC, volume: <inline-formula> <tex-math notation="LaTeX">$3.7~{\mathrm {dm}}^{3}$ </tex-math></inline-formula>) using NV centers and demonstrated its imaging of vector magnetic field at the bent portion of integrated circuit board wiring (width: <inline-formula> <tex-math notation="LaTeX">$200~{\mu }\mathrm {m}$ </tex-math></inline-formula>), which reduces footprint by more than 90% compared to magnetic imaging platforms built on top of optical platforms. In addition, a corresponding control box (volume: <inline-formula> <tex-math notation="LaTeX">$6.7~{\mathrm {dm}}^{3}$ </tex-math></inline-formula>) was designed to integrate the large equipment required for the experiment inside to improve portability. The PMC integrates the optical module and the data acquisition (DAQ) module. The control box integrates a microwave board to provide microwave signals to the PMC to control the NV centers quantum states and integrates a DAQ module to collect data. Our study shows that the experimental results are very similar to the theoretical simulation of the electromagnetic field (maximum error: 8%). The magnetic sensitivity of the PMC is about <inline-formula> <tex-math notation="LaTeX">$1.825~{\mu }\mathrm {T/Hz}^{1/2}$ </tex-math></inline-formula> with a spatial resolution of <inline-formula> <tex-math notation="LaTeX">$2.5~{\mu }\mathrm {m}$ </tex-math></inline-formula> and a temporal resolution of <inline-formula> <tex-math notation="LaTeX">$5.5~\mathbf {ms}$ </tex-math></inline-formula>. The device can be used immediately in industrial applications, where precise magnetic field imaging is required, providing a new direction in the practical application of NV centers magnetic field imaging system.

Magnetic imaging based on ensembles of diamond nitrogen‐vacancy quantum sensors has emerged as a useful technique for the spatial characterization of magnetic materials and current distributions. However, demonstrations have so far been restricted to laboratory‐based experiments using relatively bulky apparatus and requiring manual handling of the diamond sensing element, hampering broader adoption of the technique. Here a simple, compact device that can be deployed outside a laboratory environment and enables robust, simplified operation is presented. It relies on a specially designed sensor head that directly integrates the diamond sensor while incorporating a microwave antenna and all necessary optical components. This integrated sensor head is complemented by a small control unit and a laptop computer that displays the resulting magnetic image. The device is tested by imaging a magnetic sample, demonstrating a spatial resolution of 4 µm over a field of view exceeding 1 mm, and a best sensitivity of 45 µT Hz−1$\sqrt {\rm Hz}^{-1}$ per (5 µm)2 pixel. The portable magnetic imaging instrument may find use in situations where taking the sample to be measured to a specialist lab is impractical or undesirable.

In this study, we propose a compact, integrated vector magnetometer that can simultaneously measure the dynamic magnetic field at the nitrogen vacancy (NV) centers in diamond. The device is capable of converting the detected magnetic field into its respective components within a spatial coordinate system. The system employs a multi-channel phase-lock technique to retrieve magnetic field information along each NV axis from fluorescence signals captured by a single photodetector, enabling real-time vector measurements. The stability and dynamic range of the system is improved by adjusting the microwave frequency in real time.

In recent years, nitrogen-vacancy (NV) centers in diamonds have become promising solid-state magnetic sensors for applications due to their high sensitivity to magnetic fields and excellent spatial resolution at room temperature. However, the diamond magnetometer has a complex and large optical system and a microwave (MW) system, it is necessary to address the requirements of the measured environment for the small space and high sensitivity of the magnetometer in practical applications. In this article, we propose an integrated magnetometer module with magnetic flux concentrators (MFCs) shaped like the wings of an airplane. The fiber coupler, diamond, MW antenna, filters, photodetector (PD), and weak signal processing circuit are integrated into the integrated module. MFCs are also integrated to collect flux from a larger area and concentrate it into the center of the diamond magnetometer, which is used to improve the sensitivity of the diamond magnetometer. The volume of the integrated module is limited to 3.81 cm3 and achieves the actual magnetic sensitivity of sub-0.34 nT/Hz $^{\text {1/{2}}}$ . In the designed magnetometer module, the devices are assembled more easily and tightly, which provide a new degree of freedom for the production of the diamond magnetometer.

Quantum magnetometry based on optically detected magnetic resonance (ODMR) of nitrogen vacancy centers in nano- or micro-diamonds is a promising technology for precise magnetic-field sensors. Here, we propose a new, low-cost and stand-alone sensor setup that employs machine learning on an embedded device, so-called edge machine learning. We train an artificial neural network with data acquired from a continuous-wave ODMR setup and subsequently use this pre-trained network on the sensor device to deduce the magnitude of the magnetic field from recorded ODMR spectra. In our proposed sensor setup, a low-cost and low-power ESP32 microcontroller development board is employed to control data recording and perform inference of the network. In a proof-of-concept study, we show that the setup is capable of measuring magnetic fields with high precision and has the potential to enable robust and accessible sensor applications with a wide measuring range.

The fabrication of nitrogen-vacancy (NV) center magnetometers utilizing micro-electro-mechanical systems (MEMSs) has gained popularity due to the low cost, good consistency, and easy of system integration. This article presents the fabrication of an NV magnetometer using MEMS process, which integrates a silicon-based resonator for microwave transmission, a diamond waveguide for fluorescence emission, and a silicon-based reflector for fluorescence collection. The magnetometer operates on the principle of continuous-wave optically detected magnetic resonance (CW-ODMR) for magnetic field detection. The inhomogeneity of the silicon-based resonator in the <inline-formula> <tex-math notation="LaTeX">$1.9\times 1.9$ </tex-math></inline-formula> mm area of hole is 7.7%. The combined effect of the silicon-based reflector and diamond waveguide achieves a 2.82-fold enhancement in fluorescence collection efficiency. The silicon-silicon interface between the resonator and reflector components is fabricated via thermal compression bonding to form a groove for subsequent diamond waveguide integration. The processed components are placed within a ceramic tube shell and subsequently encapsulated in glass. The integrated magnetometer, with dimensions of <inline-formula> <tex-math notation="LaTeX">$14\times 14\times 12$ </tex-math></inline-formula> mm, achieves a sensitivity of 901.96 pT/Hz<inline-formula> <tex-math notation="LaTeX">${}^{1/2}$ </tex-math></inline-formula> within the 1–55 Hz, a photon shot noise limited sensitivity of 121 pT/Hz<inline-formula> <tex-math notation="LaTeX">${}^{1/2}$ </tex-math></inline-formula>, and a magnetic field detection range of <inline-formula> <tex-math notation="LaTeX">$\pm 168.2~\mu $ </tex-math></inline-formula>T.

The accurate detection of very weak biomagnetic signals with a sensitivity of fT levels and mapping nanoscale magnetic field variations are two of the most significant challenges for biosensing. Compared to the limited sensitivity and spatial resolution of traditional magnetic field sensors, quantum‐based magnetic field sensors are emerging as a promising solution. In this review, the latest developments of three representative quantum‐based magnetic field sensors, including superconducting quantum interference device (SQUID) magnetometers, spin exchange relaxation free (SERF) atomic magnetometers, and nitrogen‐vacancy centers in diamond, are summarized. Both virtues and limitations of these sensors are analyzed systematically, and typical applications in magnetocardiography, magnetoencephalography, detection of neuronal action potentials, magnetic imaging of living cells, biomedical diagnosis, etc., are presented. Furthermore, SQUIDs combined with microfluidics for magnetic immunoassay diagnostics, the chip‐scale SERF atomic magnetometers fabricated by microelectromechanical systems that offer wearable flexibility, and nanodiamonds functionalized with magnetic nanoparticles to improve the sensitivity of nanothermometers are discussed.

Thulium iron garnet (Tm3Fe5O12, TmIG) is a promising material for next-generation spintronic and quantum technologies owing to its high Curie temperature and strong perpendicular magnetic anisotropy. However, conventional magnetometry techniques are limited by insufficient spatial resolution and sensitivity to probe local magnetic phase transitions and critical spin dynamics in thin films. In this study, we present the first quantitative investigation of local magnetic field fluctuations near the Curie temperature in TmIG thin films using nitrogen-vacancy (NV) center-based quantum sensing. By integrating optically detected magnetic resonance (ODMR) and NV spin relaxometry (T1 measurements) with macroscopic techniques such as SQUID magnetometry and Hall effect measurements, we systematically characterize both the static magnetization and dynamic spin fluctuations across the magnetic phase transition. Our results reveal a pronounced enhancement in NV spin relaxation rates near 360 K, providing direct evidence of critical spin fluctuations at the nanoscale. This work highlights the unique advantages of NV quantum sensors for investigating dynamic critical phenomena in complex magnetic systems and establishes a versatile, multimodal framework for studying local phase transition kinetics in high-temperature magnetic insulators.

An integrated magnetic sensor is designed and tested that utilizes the negatively charged nitrogen vacancy centers (NVC) in diamond as a magnetic field‐sensitive quantum material, which is accessed and readout solely optically. The compact sensor device features a side length of 10 mm and includes a small HPHT diamond slab, light‐emitting diode (LED) for excitation, and integrated photodiodes. A microwave‐free approach is used. With the device, DC sensitivity to magnetic fields of 49 nA mT−1 in the range of 5–50 mT is achieved. The sensor device is also capable of detecting very small magnetic fields: Magnetic field dependencies at very low flux densities in the μT range (zero‐magnetic field) show a characteristic fluorescence behavior revealing a sensitivity of 4.8 pA μT−1. Additionally, a ray‐tracing model is applied, to identify loss mechanisms in the setup. Using this device, an ultracompact, reliable, and industry‐ready package is made available for sensor developments in industry and academia.

The localization and tracking of tiny magnetic source hold great potential for applications in the fields of medical and scientific research. However, cross-order-of-magnitude localization using millimeter sensor is an open problem. In this article, we proposed a precise localization method for the tiny magnetic source that breaks through the limited field-of-view of the optical quantum sensor imaging. The position of the magnetic source is uniquely resolved by the construction of a magnetic gradient tensor (MGT) based on the vector magnetic field (2.7 <inline-formula> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2.7 mm, pixel size: <inline-formula> <tex-math notation="LaTeX">$3.45~\mu \text{m}$ </tex-math></inline-formula>) obtained by nitrogen-vacancy (NV) color centers in a diamond. A 3 mm diameter magnetic source is accurately located within a spatial range of 5 cm with a mean error of 8%. In addition, the limitations and influencing factors of the NV-MGT localization method are theoretically discussed. The results provide insight into the localization of tiny magnetic sources and extend the application of quantum sensor.

Various techniques have been applied to visualize superconducting vortices, providing clues to their electromagnetic response. Here, we present a wide-field, quantitative imaging of the stray field of the vortices in a superconducting thin film using perfectly aligned diamond quantum sensors. Our analysis, which mitigates the influence of the sensor inhomogeneities, visualizes the magnetic flux of single vortices in YBa2Cu3O7−δ with an accuracy of ±10%. The obtained vortex shape is consistent with the theoretical model, and penetration depth and its temperature dependence agree with previous studies, proving our technique's accuracy and broad applicability. This wide-field imaging, which in principle works even under extreme conditions, allows the characterization of various superconductors.

We present a new magnetometry method integrating an ensemble of nitrogen-vacancy (NV) centers in a single-crystal diamond with an extended dynamic range for monitoring a fast changing magnetic-field. The NV-center spin resonance frequency is tracked using a closed-loop frequency locked technique with fast frequency hopping to achieve a 10 kHz measurement bandwidth, thus allowing for the detection of fast changing magnetic signals up to 0.723 T/s. This technique exhibits an extended dynamic range subjected to the working bandwidth of the microwave source. This extended dynamic range can reach up to 4.3 mT, which is 86 times broader than the intrinsic dynamic range. The essential components for NV spin control and signal processing, such as signal generation, microwave frequency control, data processing, and readout, are integrated in a board-level system. With this platform, we demonstrate a broadband magnetometry with an optimized sensitivity of 4.2 nT Hz-1/2. This magnetometry method has the potential to be implemented in a multichannel frequency locked vector magnetometer suitable for a wide range of practical applications, such as magnetocardiography and high-precision current sensors.

ABSTRACT Magnetometry plays an important role in exploring the deep sea, which is one of the Earth’s final unknown frontiers. However, the complexity of the marine environment and the limitations of conventional magnetometers restrict its in-depth application. The nitrogen-vacancy (NV) center in diamond offers a potential solution to encompass and transcend conventional ocean magnetometers. Its unique advantages, such as precise vector measurement and tolerance to extreme environments, make it well suited for deep-sea applications like navigation. This work introduces the first deep-sea quantum vector magnetometer based on NV centers. The performance of this magnetometer is effectively validated by a series of field tests on the manned submersible Shenhai Yongshi during a cruise in the South China Sea, including an experimental underwater navigation using the diamond quantum sensor as a magnetic compass. This successful deep-sea application marks a milestone for transforming this promising solid-state spin quantum system into a practical sensor for real-world marine applications.

Vector magnetometry provides more information than scalar measurements for magnetic surveys utilized in space, defense, medical, geological and industrial applications. These areas would benefit from a mobile vector magnetometer that can operate in extreme conditions. Here we present a scanning fiber-coupled nitrogen vacancy (NV) center vector magnetometer. Feedback control of the microwave excitation frequency is employed to improve dynamic range and maintain sensitivity during movement of the sensor head. Tracking of the excitation frequency shifts for all four orientations of the NV center allow us to image the vector magnetic field of a damaged steel plate. We calculate the magnetic tensor gradiometry images in real time, and they allow us to detect smaller damage than is possible with vector or scalar imaging.

Diamond nitrogen-vacancy (NV) center has been widely studied as a high-sensitivity solid-state quantum sensor with a wide range of applications, including magnetometry, thermometry manometry, and chemical sensing. However, its application in practical scenarios remains challenging due to difficulties of component manufacturing, miniaturization, and integration for NV control and readout. Here, we demonstrate an all-electric driving diamond sensor fabricated using standard microfabrication processes and micro-assembly, achieving integration of five key components—laser diode, diamond, microwave antenna, long pass filter, and photodiode in a hermetically sealed package case, with dimensions of 2.72 cm3. The integrated diamond magnetometer achieved a magnetic sensitivity of 2.25 nT · Hz−1/2. Additionally, the inherent crystallographic axes of the diamond are used to simultaneously detect vector magnetic field signals. The design and fabrication process allows for wafer-level assembly, enabling low-cost mass-production and easy integration with peripheral circuits.

Nitrogen‐vacancy (NV) centers in diamond exhibit magnetic‐field‐sensitive quantum properties and possess four distinct crystallographic orientations, establishing a robust foundation for vector magnetic sensing. However, NV‐based vector magnetic field sensors are plagued by high demodulation complexity and cost arising from cross‐talk among NV orientations, in addition to the challenge of limited sensitivity. Here, we present a diamond NV fiber‐optic planar vector magnetometer that enables direct readout of magnetic components with high sensitivity. This is achieved through a novel alignment scheme based on the NV centers intrinsic orientations, which suppresses cross‐talk to below 2%. Meanwhile, a magneto‐optically co‐enhanced strategy is implemented by integrating two pairs of magnetic flux concentrators and optimizing the polarization of excitation light, leading to a nearly 20‐fold improvement in sensitivity. Furthermore, the real‐time readout capability and overall performance are experimentally validated under dynamic magnetic field variations in realistic scenarios. Our work provides a viable solution for high‐performance NV‐based vector magnetometry with simplified demodulation, facilitating its application in areas such as magnetic anomaly detection.

In this research, we present a hermetically sealed integrated diamond magnetometer for vector magnetometry. The diamond chip, fabricated using standard microfabrication processes, has a volume of 0.1 cm3. The case integrates five essential components for driving quantum state detection, including laser diode, microwave antenna, diamond chip, long-pass filter, and photodiode, with an overall volume of 2.72 cm3, The integrated diamond magnetometer achieved a magnetic sensitivity of $2.62\ \text{nT}\cdot \text{Hz}^{-1/2}$, and enables real-time measurement and reconstruction of the spatial vector magnetic tensor by leveraging the inherent crystallographic axes of the diamond. The highly integrated sensor with all electrical 10 paves the way towards industrial applications.

Vector magnetometers based on the optically detected magnetic resonance (ODMR) of nitrogen-vacancy centers in diamond are being developed for applications such as navigation and geomagnetism. However, at low magnetic fields, such as that on Earth (∼50µT), diamond magnetometers suffer from spectral congestion whereby ODMR peaks are not easily resolved. Here, we experimentally investigate a potential solution of using an isotropic, three-dimensional magnetic flux concentrator to amplify Earth’s field without altering its direction. The concentrator consists of six ferrite cones, in a face-centered cubic arrangement, centered about a diamond. We vary the direction of a 50µT applied field and record and fit the resulting ODMR spectra. By comparing the fitted fields to those of a reference fluxgate magnetometer, we characterize the angular response of the diamond magnetometer and quantify absolute errors in the field magnitude and angle. We find that the enhancement factor is nearly isotropic, with a mean of 19.05 and a standard deviation of 0.16, when weighted by solid angle coverage. Gradient broadening of the ODMR lines is sufficiently small that the spectra are well resolved for nearly all field directions, alleviating spectral congestion. For ∼98% of the total 4π solid angle, Cramér-Rao lower bounds for magnetic field estimation uncertainty are within a factor of 2 of those of the fully resolved case, indicating minimal deadzones. We track the stability of the magnetometer over 6 h and observe variations ≲40nT/h, limited by temperature drift. Our study presents a route for diamond vector magnetometry at Earth’s field, with potential applications in geomagnetic surveys, anomaly detection, and navigation.

Vector magnetometry using an ensemble of nitrogen-vacancy (NV) centers holds great promise across a wide range of applications. Since NV centers are sensitive to external magnetic fields projected onto their crystallographic axes, distinguishing NV centers with different orientations is essential for fully extracting vectorial magnetic field information. While a calibrated magnetic bias field or optical polarization has been widely used for this purpose, the use of microwave fields remains relatively unexplored. Here, we demonstrate the identification of NV axes using the spatial variation of microwave magnetic fields generated by a microwave loop structure. Continuous-wave optically detected magnetic resonance scanned over the NV center ensemble shows distinct patterns that align well with a simplified model for each NV axis. After identifying the NV axes, we reconstruct the magnitude and orientation of the external magnetic field. This technique expands the potential for miniaturizing and enhancing NV-based vector magnetic sensors.

Wide-field imaging of magnetic signals using ensembles of nitrogen-vacancy (NV) centers in diamond has garnered increasing interest due to its combination of micron-scale resolution, millimeter-scale field of view, and compatibility with diverse samples from across the physical and life sciences. Recently, wide-field NV magnetic imaging based on the Ramsey protocol has achieved uniform and enhanced sensitivity compared to conventional measurements. Here, we integrate the Ramsey-based protocol with spin-bath driving to extend the NV spin dephasing time and improve magnetic sensitivity. We also employ a high-speed camera to enable dynamic wide-field magnetic imaging. We benchmark the utility of this quantum diamond microscope (QDM) by imaging magnetic fields produced from a fabricated wire phantom. Over a 270 × 270 μm2 field of view, a median per-pixel magnetic sensitivity of 4.1(1) nT /Hz is realized with a spatial resolution ≲ 10 μm and sub-millisecond temporal resolution. Importantly, the spatial magnetic noise floor can be reduced to the picotesla scale by time-averaging and signal modulation, which enables imaging of a magnetic-field pattern with a peak-to-peak amplitude difference of about 300 pT. Finally, we discuss potential new applications of this dynamic QDM in studying biomineralization and electrically active cells.

Wide-field magnetic imaging based on nitrogen-vacancy (NV) centers in diamond has been shown the applicability in material and biological science. However, the spatial resolution is limited by the optical diffraction limit (>200 nm) due to the optical real-space localization and readout of NV centers. Here, we report the wide-field Fourier magnetic imaging technique to improve spatial resolution beyond the optical diffraction limit while maintaining the large field of view. Our method relies on wide-field pulsed magnetic field gradient encoding of NV spins and Fourier transform under pixel-dependent spatial filters. We have improved spatial resolution by a factor of 20 compared to the optical resolution and demonstrated the wide-field super-resolution magnetic imaging of a gradient magnetic field. This technique paves a way for efficient magnetic imaging of large-scale fine structures at the nanoscale.

Scanning-probe and wide-field magnetic microscopes based on nitrogen-vacancy (NV) centers in diamond have enabled advances in the study of biology and materials, but each method has drawbacks. Here, we implement an alternative method for nanoscale magnetic microscopy based on optical control of the charge state of NV centers in a dense layer near the diamond surface. By combining a donut-beam super-resolution technique with optically detected magnetic resonance spectroscopy, we imaged the magnetic fields produced by single 30 nm iron-oxide nanoparticles. The magnetic microscope has a lateral spatial resolution of ∼100 nm, and it resolves the individual magnetic dipole features from clusters of nanoparticles with interparticle spacings down to ∼190 nm. The magnetic feature amplitudes are more than an order of magnitude larger than those obtained by confocal magnetic microscopy due to the narrower optical point-spread function and the shallow depth of NV centers. We analyze the magnetic nanoparticle images and sensitivity as a function of the microscope's spatial resolution and show that the signal-to-noise ratio for nanoparticle detection does not degrade as the spatial resolution improves. We identify sources of background fluorescence that limit the present performance, including diamond second-order Raman emission and imperfect NV charge state control. Our method, which uses <10 mW laser power and can be parallelized by patterned illumination, introduces a promising format for nanoscale magnetic imaging.

As a highly sensitive quantum magnetometer, the diamond nitrogen-vacancy (NV) center is capable of operating in extreme environments such as high temperature and pressure. When coupled with a wide-area imaging sensor, it enables wide-field imaging with spatial resolution close to the optical limit, providing an innovative approach to wide-field magnetic imaging in various fields, including medical visualization, basic scientific research, and electronic circuit anomaly diagnosis. Conventionally, optical detection magnetic resonance (ODMR) enables the measurement of magnetic field for the diamond NV centers. However, obtaining the ODMR requires continuous sweeping of a long microwave bandwidth, inducing long blind area errors that limit imaging speed and reduce practical application. To mitigate ODMR sweep time, we introduce a diamond NV center microscope based on a multichannel control system (MCCS). The MCCS realizes intermittent frequency sweeping, enabling it to eliminate the ODMR transition Section and collect only segments containing spin information. This novel approach reduces acquisition time and speeds up computer solution speed. To validate the effectiveness of our proposed system, we perform magnetic field imaging of the printed circuit board (PCB). At the same testing conditions, the MCCS-based system enables six times acquisition speed compared to continuous-wave ODMR (CW-ODMR) and confidence to 95%.

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Widefield magnetic imaging using ensembles of nitrogen‐vacancy (NV) centres in diamond has emerged as a useful technique for studying the microscopic magnetic properties of materials. Thus far, this technique is mainly implemented on custom‐made optical microscopes. An add‐on is developed for a standard laboratory optical microscope that integrates the NV‐diamond sensor and necessary light source, microwave antenna, and bias magnet, enabling NV‐based magnetic imaging while retaining the typical optical measurement modes of the microscope. The retrofitted quantum diamond microscope is demonstrated by imaging a magnetic particle sample using brightfield, darkfield, and magnetic imaging modes. Furthermore, an iso‐magnetic field imaging technique is employed to visualize the magnetic field of the sample within seconds, and finally demonstrate 3D stray field imaging. Retrofitting existing microscopes exploits the stability and high quality of traditional optical microscope systems while reducing the cost and space requirements of establishing a standalone magnetic imaging system.

… serve as versatile multi-physical field sensors capable of measuring magnetic fields, … measuring magnetic field and temperature variations by directly solving the Hamiltonian of an NV …

Three-dimensional magnetic imaging with high spatio-temporal resolution is critical for probing current paths in various systems, from biosensing to microelectronics. Conventional 2D Fourier-based current source localization methods are ill-posed in multilayer or dynamic systems due to signal overlap and noise. In this work, we demonstrate an innovative nitrogen-vacancy (NV) center-based wide-field magnetic microscopy technique for dynamic three-dimensional imaging and localization of current sources. Using custom-fabricated multilayer micro-coil platform to emulate localized, time-varying currents similar to neuronal activity, we acquire magnetic field maps with micrometre-scale spatial and millisecond-scale temporal resolution using per-pixel lock-in-based detection. Source localization and image reconstruction are achieved using a Least Absolute Shrinkage and Selection Operator (LASSO)-based reconstruction framework that incorporates experimentally measured basis maps as spatial priors. Our method enables robust identification of active current sources across space and time, and significantly advances the accuracy of dynamic 3D current imaging and NV-based magnetometry for complex systems.

Rock magnetic microscopy (RMM) has emerged as an advanced methodology for imaging the magnetization distribution of geological thin sections under ambient conditions, providing precise information with high spatial resolution and high magnetic field sensitivity; however, several factors---including the large size and complexity of sensors, their low magnetic field sensitivity and small field of view, and the need for cryogenic conditions---have impeded the widespread adoption of current RMM setups. Here, we present a room-temperature, fiber-coupling, scanning scheme for RMM based on the negatively charged nitrogen-vacancy (NV) centers in diamond. A $200\ifmmode\times\else\texttimes\fi{}200\ifmmode\times\else\texttimes\fi{}50\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}{\mathrm{m}}^{3}$ diamond chip is glued to a multimode fiber ferrule for scanning imaging of the magnetic field. To ensure the precision of the magnetic field measurements, the diamond surface is coated with a reflective gold film. A spatial resolution of $180\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\mathrm{m}$ and a magnetic field sensitivity of $52\phantom{\rule{0.2em}{0ex}}\mathrm{nT}/{\mathrm{Hz}}^{1/2}$ in the near-dc frequency range below 10 Hz are achieved. This performance corresponds to a sensitivity of ${10}^{\ensuremath{-}12}\phantom{\rule{0.2em}{0ex}}\mathrm{A}\phantom{\rule{0.1em}{0ex}}{\mathrm{m}}^{2}/{\mathrm{Hz}}^{1/2}$ for magnetic moment measurements, approaching that of the superconducting rock magnetometer. The stray magnetic field distribution on a banded iron formation thin section is successfully scanned, revealing the inhomogeneous distribution of magnetization within the iron-rich bands. This study demonstrates the potential to extend the application scope of NV magnetometry in the frontiers of high-resolution geological research.