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.
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.
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.
High-resolution wide-spectrum measurement techniques have important applications in fields such as astronomy, wireless communication, and medical imaging. Nitrogen-vacancy (NV) center in diamond is well known for its high stability, high sensitivity, real-time monitoring, single-point detection, and suitability for long-term measurement, and has an outstanding choice for spectrum analyzers. Currently, spectrum analyzers based on NV centers as detectors can perform real-time spectrum analysis in the range of several tens of gigahertz, but their frequency resolution is limited to a MHz level. In this study, we construct a quantum diamond microwave spectrum imaging system by combining continuous wave-mixing techniques. According to the spin-related properties of the NV center in diamond, we implement optical pumping by 532 nm green laser light illuminating the diamond NV center. A spherical magnet is used to produce a magnetic field gradient along the direction of the diamond crystal. By adjusting the size and direction of the magnetic field gradient, spatial encoding of the resonance frequency of the NV center is achieved. The magnetic field gradient induces the Zeeman effect on the diamond surface at different positions, generating corresponding ODMR signals. Through accurate programming, we coordinate the frequency scanning step size of the microwave source with the camera exposure and image storage time, and synchronize them circularly according to the order of image acquisition. Ultimately, after algorithmic processing, we successfully obtain comprehensive spectrum data in a range from 900 MHz to 6.0 GHz. Within the measurable spectrum range, the system employs continuous wave-mixing, simultaneously applying resonant microwaves and slightly detuning auxiliary microwaves to effectively excite the NV center. This method triggers off microwave interference effects, disrupting the balance between laser-induced polarization and microwave-induced spontaneous relaxation. Specifically, microwave interference causes the phase and amplitude of the fluorescence signal to change, leading to the generation of alternating current fluorescence signals. This further enhances the response of the NV magnetometer to weak microwave signals. The method enables the system to achieve a frequency resolution of 1 Hz in the measurable spectrum range, and it can separately measure the frequency resolution of multiple frequency points with a frequency step size of 1 MHz. The research results indicate that the wide-spectrum measurement based on NV centers can achieve sub-hertz frequency resolution, providing robust technical support for future spectrum analysis and applications.
A simple and convenient design enables real-time three-dimensional position tracking of nitrogen-vacancy (NV) centers in diamond. The system consists entirely of commercially available components (a single-photon counter, a high-speed digital-to-analog converter, a phase-sensitive detector-based feedback device, and a piezo stage), eliminating the need for custom programming or rigorous optimization processes. With a large input range of counters and trackers combined with high sensitivity of single-photon counting, high-speed position tracking (upper bound recovery time of 0.9 s upon 250 nm of step-like positional shift) not only of bright ensembles, but also of low-photon-collection-efficiency single to few NV centers (down to 103 s−1) is possible. The tracking requires position modulation of only 10 nm, which allows simultaneous position tracking and pulsed measurements in the long term. Therefore, this tracking system enables measuring a single-spin magnetic resonance and Rabi oscillations at a very high resolution even without photon collection optimization. The system is widely applicable to various fields related to NV center quantum manipulation research such as NV optical trapping, NV tracking in fluid dynamics, and biological sensing using NV centers inside a biological cell.
Abstract We demonstrate a method for thermal detection that is the sensitivity 6.2 mK Hz −1 2 , which uses the frequency lock closed-loop scheme to track Zeeman-split resonance of nitrogen-vacancy (NV) centers in diamond. The NV diamond surface acts as a temperature measurement sensor to transfer the temperature variation as D ( T ) parameter change to lead to the movement of the energy levels to detect the temperature. By frequency modulation technology and closed-loop feedback locking technology, automatic temperature detection and step signal reading are realized, with a resolution of 7.6 mK. It is found that the closed-loop output is basically unchanged, while the open-loop output has an error signal proportional to the laser fluctuation. The closed-loop feedback technique can improve the stability and resolution of the system and provides a method for measuring the actual temperature detection. Such a demonstration marks a vital advance in transitioning the NV thermometer from a laboratory system to a functional device for detecting temperature fields in a practical environment.
The nitrogen-vacancy center in diamond has been broadly applied in quantum sensing since it is sensitive to different physical quantities. Meanwhile, it is difficult to isolate disturbances from unwanted physical quantities in practical applications. Here, we present a fiber-based quantum thermometer by tracking the sharp-dip in the zero-field optically detected magnetic resonance spectrum in a high-density nitrogen-vacancy ensemble. Such a scheme can not only significantly isolate the magnetic field and microwave power drift but also improve the temperature sensitivity. Thanks to its simplicity and compatibility in implementation and robustness, this quantum thermometer is then applied to the surface temperature imaging of an electronic chip with a sensitivity of 18mK/Hz. It thus paves the way to high sensitive temperature measurements in ambiguous environments.
Nitrogen—Vacancy (NV) center in diamond can detect tiny magnetic field due to relative long coherence time even at room temperature. Its optical accessibility and capability of thin-film formation provide us an interesting sensing modality such as wide field imaging. We have reported phase sensitive protocol for ac magnetic field designed for wide field setup.[1] In this study we demonstrate an application of phase sensitive protocol; measuring distribution of ac magnetic field strength by phase sensing. Previous methods of multi-pulse quantum sensing such as XY8 realize quite high sensitivity of ac magnetic field. Since XY8 has dependencies on strength and phase of ac magnetic field, it is necessary to adjust ac phase to an optimal point in order to obtain a best sensitivity, and we cannot distinguish the effect of amplitude and phase. Recent studies have showed utilizing time-domain information is effective for improving frequency resolution of quantum sensing,[2,3] and we found same technique is also effective for simultaneous measurement of strength and phase. Here we propose a robust method for amplitude estimation by phase sensing. We added another signal for reference, then sensing phase difference between target signal and reference can be converted into amplitude. Conventional XY8 sensing is based upon fluorescence measurement which can be affected easily by many obstacles such as stray light, autofluorescence, and fringes of excitation laser. In the other hand, our method can be more robust because it is based on phase measurement. Nothing can change the phase except absorption of ac signal. This work was supported by MEXT Q-LEAP, CAO PRISM, Japan. [1] Mizuno et al., AIP advances 2018 [2][3] Boss, Schmitt