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arXiv:2512.05986

Detuning-insensitive wide-field imaging of vector microwave fields with diamond sensors

Xiu-Qi Chen, Rui-Zhi Zhang, Gang-Qin Liu, Huijie Zheng

physics.ins-detcond-mat.mes-hallquant-phSubmitted Nov 28, 2025• Announced Dec 1, 2025
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Abstract

Nitrogen vacancy (NV) centers in diamond have precipitated profound advances in microwave detection, manifesting themselves both in spatial resolution and sensitivity. However, typical methods based on Rabi oscillations are subject to detunings due to thermal and magnetic fluctuations and/or gradients, which introduce systematic errors and render the measurements susceptible to environmental perturbations. Here, we propose and demonstrate a novel approach for determining both the magnitude and direction of microwaves, by exploiting the spectral line broadening effect in the optically detected magnetic resonance of NV centers. This method eliminates the requirement of aligning the MW frequency to the spin transitions and is therefore immune to variations and inhomogeneities of the magnetic field and temperature, providing an optimal tool for fast imaging applications. With this method, we achieved wide-field imaging of near field microwaves generated with a microscale $\rmΩ$-pattern antenna with a resolution of 800\,nm. Combining with the vector detection using multi-axis NVs, a full reconstruction of the vector microwave fields is obtained. Besides, our scheme also exhibits excellent linearity over a broad range of MW amplitudes, and the scale is theoretically calculated to be more than four orders. Our results augment the applicability of diamond-based microwave devices in applications under complex scenarios, especially where large dynamic range, fast test speed, and high spatial resolution are demanded.

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Nitrogen vacancy (NV) centers in diamond have precipitated profound advances in microwave detection, manifesting themselves both in spatial resolution and sensitivity. However, typical methods based on Rabi oscillations are subject to detunings due to thermal and magnetic fluctuations and/or gradients, which introduce systematic errors and render the measurements susceptible to environmental perturbations. Here, we propose and demonstrate a novel approach for determining both the magnitude and direction of microwaves, by exploiting the spectral line broadening effect in the optically detected magnetic resonance of NV centers. This method eliminates the requirement of aligning the MW frequency to the spin transitions and is therefore immune to variations and inhomogeneities of the magnetic field and temperature, providing an optimal tool for fast imaging applications. With this method, we achieved wide-field imaging of near field microwaves generated with a microscale Ω\rmΩΩ-pattern antenna with a resolution of 800,nm. Combining with the vector detection using multi-axis NVs, a full reconstruction of the vector microwave fields is obtained. Besides, our scheme also exhibits excellent linearity over a broad range of MW amplitudes, and the scale is theoretically calculated to be more than four orders. Our results augment the applicability of diamond-based microwave devices in applications under complex scenarios, especially where large dynamic range, fast test speed, and high spatial resolution are demanded.
This study introduces a method for reconstructing vector microwave magnetic fields using a single nitrogen-vacancy (NV) center in locally strong effective fields with two different orientations in diamond, without the previously required external magnetic field. Due to the varying orientations of the effective fields, NV centers exhibit two distinct sets of switchable ground states. The resonant Rabi oscillations of an NV center in these two distinct states were utilized to reconstruct vector microwave magnetic fields. Remarkably, this technique achieves an angular resolution of 0.02 mrad/Hz. Overcoming the limitations inherent in previous practices of using NV ensembles, this breakthrough has the potential to substantially enhance both the spatial resolution and the sensitivity of microwave magnetic field imaging, a meaningful development for various scientific and technological 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.
Abstract Imaging of microwave magnetic fields with nano-scale resolution has interesting applications. Specifically, detecting the orientation of microwave fields is useful in condensed matter physics and quantum control. However, most of the existing methods for microwave field imaging are limited to detecting the magnitude of the fields. Due to their small sensor size and favorable optical and spin properties, nitrogen-vacancy (NV) centers in diamond are highly suitable for imaging dc and ac magnetic fields. The reported methods for detecting the direction of microwave magnetic fields use pulsed Rabi frequency measurements. Here, we demonstrate imaging of the direction of linearly polarized microwave magnetic fields using only continuous-wave experiments on NV centers. This simplifies the sensor apparatus and is particularly advantageous in applications where pulsing of the target microwave field is not possible. The method requires a static bias magnetic field oriented perpendicular to the quantization axis of NV centers. We detect the direction of an arbitrary microwave magnetic field using NV centers of two different orientations of an NV ensemble. Moreover, we demonstrate that the projection of the microwave fields onto a plane can be imaged using NV centers of a single orientation. This can be straightforwardly implemented using a single NV center.
The measurement of vector magnetic fields with high sensitivity and spatial resolution is important for both fundamental science and engineering applications. In particular, magnetic-field sensing with nitrogen-vacancy (NV) centers in diamond is a promising approach that can outperform existing methods. Recent studies have demonstrated vector dc magnetic-field sensing with perfectly aligned NV centers, which showed a higher readout contrast than NV centers having four equally distributed orientations. However, to estimate the azimuthal angle of the target magnetic field with respect to the NV axis in these previous approaches, it is necessary to apply a strong reference dc magnetic field, which can perturb the system to be measured. This is a crucial problem, especially when attempting to measure vector magnetic fields from materials that are sensitive to applied dc magnetic fields. Here, we propose a method to measure vector dc magnetic fields using perfectly aligned NV centers without reference dc magnetic fields. This method can be performed even with a single NV center. More specifically, we use the direction of linearly polarized microwave fields to induce Rabi oscillation as a reference and we estimate the azimuthal angle of the target fields from the Rabi frequency. We further demonstrate the potential of our method to improve sensitivity by using entangled states to overcome the standard quantum limit. Our method of using a reference microwave field is an alternative technique for sensitive vector dc magnetic-field sensing.
Microwave (MW) magnetometry utilizing nitrogen-vacancy (NV) centers in diamond offers a broad, tunable detection bandwidth enabled by the magnetic-field-dependent electron spin resonances (ESR) of the NV centers. In this work, we present and experimentally demonstrate two NV-based protocols for spectral analysis of amplitude-modulated (MW) signals. The first protocol employs the NV center as a bandpass filter and reconstructs frequency-domain information of MW signals by sweeping the MW carrier frequency. The second protocol achieves optical imaging of the MW spectrum using an NV-based quantum spectrum analyzer, wherein a magnetic field gradient spatially maps the ESR frequencies of the NV centers, enabling parallel detection of multiple spectral components over a wide instantaneous bandwidth. Both protocols show results that agree well with reference measurements from a classical spectrum analyzer. Our approaches extend the application of spin-based quantum sensors to the field of modern communications and can be adapted for other spin-based quantum sensors.
High-resolution, high-sensitivity microwave (MW) magnetic field imaging is indispensable for non-destructive integrated circuit (IC) testing, radio-frequency device characterization, and spintronic research. Yet, the practical utility of these techniques is severely constrained by the pervasive challenge of isolating weak magnetic signatures from intense optical and electronic noise, which fundamentally limits both acquisition speed and detection sensitivity. Here, we overcome this barrier by introducing a wide-field imaging scheme based on an ensemble of diamond nitrogen-vacancy (NV) centers, synergistically combined with digital lock-in amplification (DLA). By exploiting digital demodulation, the DLA precisely extracts the MW-field response at a specific modulation frequency from background noise (e.g., laser intensity fluctuations), dramatically improving the signal-to-noise ratio (SNR). Consequently, our system attains a magnetic field sensitivity of 126 nT/(Hz)\sqrt(Hz)(​Hz). Critically, the unprecedented SNR permits a pixel dwell time of under one millisecond, allowing full-field images to be acquired within seconds-more than an order of magnitude faster than state-of-the-art NV-based wide-field techniques. This combination of speed, sensitivity, and micron-scale spatial resolution (1.6 μμμm) paves the way for quasi-real-time, non-invasive diagnostics of dynamic MW devices and integrated circuits.