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.
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.
We demonstrate a robust, scale-factor-free vector magnetometer, which uses a closed-loop frequency-locking scheme to simultaneously track Zeeman-split resonance pairs of nitrogen-vacancy (NV) centers in diamond. This technique offers a three-orders-of-magnitude increase in dynamic range compared to open-loop methodologies; is robust against fluctuations in temperature, resonance linewidth, and contrast; and allows for simultaneous interrogation of multiple transition frequencies. By directly detecting the resonance frequencies of NV centers oriented along each of the diamond's four tetrahedral crystallographic axes, we perform full vector reconstruction of an applied magnetic field.
The nitrogen-vacancy centers in diamond have exhibited excellent sensing capabilities. By applying the resonance frequency tracking (RFT) method in a closed-loop system, magnetic-field measurements with a wide dynamic range have been demonstrated. However, the previous strategies employ phase-sensitive control signals, which degrade control robustness and reduce tracking rates, thereby impeding real-time measurements. Here, an amplitude–phase joint discrimination strategy is proposed to improve robustness, overcoming the limitations of existing strategies that are sensitive to phase delays in fluorescence signal transmission. Moreover, to improve the tracking speed, a customized device, integrating a fast-response lock-in amplifier (LIA) and a frequency-agile microwave (MW) source, is reported. The LIA achieves a response time as short as 20 μs, while the MW source reaches a frequency switching time of 1 μs. The proposed strategy and customized device are implemented and evaluated on an all-fiber quantum current sensing system. Test results show that the system achieves a maximum sampling rate of 20 kHz, with excellent linearity (a linear deviation of 0.37% over the range of 0-120 A) and high accuracy (a measurement error of 0.73% at 80 A), making it promising for a wide range of high-speed quantum measurement scenarios.
In modern-day quantum metrology, quantum sensors are widely employed to detect weak magnetic fields or nanoscale signals. Quantum devices, exploiting quantum coherence, are inevitably connected to physical constants and can achieve accuracy, repeatability, and precision approaching fundamental limits. As a result, these sensors have shown utility in a wide range of research domains spanning both science and technology. A rapidly emerging quantum sensing platform employs atomic-scale defects in crystals. In particular, magnetometry using nitrogen-vacancy (NV) color centers in diamond has garnered increasing interest. NV systems possess a combination of remarkable properties, optical addressability, long coherence times, and biocompatibility. Sensors based on NV centers excel in spatial resolution and magnetic sensitivity. These diamond-based sensors promise comparable combination of high spatial resolution and magnetic sensitivity without cryogenic operation. The above properties of NV magnetometers promise increasingly integrated quantum measurement technology, as a result, they have been extensively developed with various protocols and find use in numerous applications spanning materials characterization, nuclear magnetic resonance (NMR), condensed matter physics, paleomagnetism, neuroscience and living systems biology, and industrial vector magnetometry. In this chapter, NV centers are explored for magnetic sensing in a number of contexts. In general, we introduce novel regimes for magnetic-field probes with NV ensembles. Specifically, NV centers are developed for sensitive magnetometers for applications where microwaves (MWs) are prohibitively invasive and operations need to be carried out under zero ambient magnetic field. The primary goal of our discussion is to improve the utility of these NV center-based magnetometers.
Sensing vector magnetic fields is important to many applications in fundamental physics, bioimaging, and materials science. Sensors exploiting nitrogen-vacancy (N-V) centers typically interrogate N-V ensembles oriented in all directions, thwarting nanoscale spatial resolution. Utilizing the level anticrossing in the triplet ground state, the authors demonstrate a $m\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}c\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}w\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}v\phantom{\rule{0}{0ex}}e\ensuremath{-}f\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}e$ vector magnetometer that simultaneously measures all Cartesian components of the field, offering wide-band operation and high, equal sensitivity in all directions. This technique may work for single N-V centers as well as ensembles, extending vector measurements to the nanoscale, at ambient temperatures.
Negatively charged nitrogen-vacancy (NV) centers in diamond have been extensively studied as a promising high sensitivity solid-state magnetic field sensor at room temperature. However, their use for current sensing applications is limited due to the challenge of integration and miniaturization of the diamond NV sensor. Here, we demonstrate an integrated NV sensor fabricated with standard microfabrication process. The sensor device incorporated with a toroidal magnetic yoke enables a high-precision wide range direct current sensing with galvanic isolation. The performance of the diamond NV current sensor in an open loop configuration has been investigated. A current measuring range of 0 A ~ 1000 A with an uncertainty of 46 ppm are achieved. Taking advantage of dual spin resonance modulation, temperature drift is suppressed to 10 ppm/K. This configuration opens new possibilities as a robust and scalable platform for current quantum sensing technologies.
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 fT / Hz . 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.