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arXiv:2606.05928 · Japanese Journal of Applied Physics

Broadband AC Magnetic Field Sensing via Continuous wave optically detected magnetic resonance with NV Centers in diamond

Ryohei Dokai, Ryusei Okaniwa, Miku Ishizaki, Junko Ishi-Hayase, Yuichiro Matsuzaki

quant-phSubmitted Jun 4, 2026• Announced Jun 5, 2026• 0 citations
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Abstract

The nitrogen-vacancy (NV) center in diamond has attracted considerable attention as a highly sensitive quantum sensor that can operate at room temperature. In particular, continuous-wave optically detected magnetic resonance (CW-ODMR) is promising for a wide range of applications because of its simplicity. However, conventional AC magnetic-field sensing schemes based on CW-ODMR suffer from a limited detection bandwidth: the detectable frequency is either fixed by intrinsic physical parameters of the NV center or, even when tunable, restricted to a narrow range of only a few MHz. Here, we propose a broadband AC magnetometry scheme based on CW-ODMR with NV centers using microwave-driven dressed states.Through theoretical analysis and numerical simulations, we show that the proposed scheme enables the detection of AC magnetic fields with frequencies up to the order of 100 MHz, which has been difficult to achieve using conventional CW-ODMR-based methods.

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The nitrogen-vacancy (NV) center in diamond has attracted considerable attention as a highly sensitive quantum sensor that can operate at room temperature. In particular, continuous-wave optically detected magnetic resonance (CW-ODMR) is promising for a wide range of applications because of its simplicity. However, conventional AC magnetic-field sensing schemes based on CW-ODMR suffer from a limited detection bandwidth: the detectable frequency is either fixed by intrinsic physical parameters of the NV center or, even when tunable, restricted to a narrow range of only a few MHz. Here, we propose a broadband AC magnetometry scheme based on CW-ODMR with NV centers using microwave-driven dressed states.Through theoretical analysis and numerical simulations, we show that the proposed scheme enables the detection of AC magnetic fields with frequencies up to the order of 100 MHz, which has been difficult to achieve using conventional CW-ODMR-based methods.
The nitrogen-vacancy (NV) center is a promising candidate to realize practical quantum sensors with high sensitivity and high spatial resolution at room temperature and atmospheric pressure. In conventional high-frequency AC magnetometry with NV centers, the setup requires a pulse sequence with an appropriate time synchronization and strong microwave power. To avoid these practical difficulties, AC magnetometry using continuous-wave optically detected magnetic resonance (CW-ODMR) was recently demonstrated. That previous study utilized radio frequency (RF)-dressed states generated by the coherent interaction between the electron spin of the NV center and the RF wave. However, the drawback of this method is that the detectable frequency of the AC magnetic fields is fixed. Here, we propose and demonstrate frequency-tunable magnetic field sensing based on CW-ODMR. In the new sensing scheme, we obtain RF double-dressed states by irradiation with RF fields at two different frequencies. One creates the RF-dressed states and changes the frequency of the target AC field. The other is a target AC field that induces a change in the CW-ODMR spectrum by generating the RF double-dressed states through coherent interaction with the RF-dressed states. The sensitivity of our method is estimated to be comparable to or even higher than that of the conventional method based on the RF field with a single frequency. The estimated bandwidth is 7.5 MHz, higher than that of the conventional method using the RF-dressed states. Our frequency-tunable magnetic field sensor based on CW-ODMR paves the way for new applications in diamond devices.
Nitrogen-vacancy (NV) centers in diamond are promising quantum sensors for AC magnetic fields. However, conventional dynamical-decoupling-based magnetometry becomes technically demanding at high frequencies because of the requirement for increasingly short and high-power microwave pulses. This paper describes an AC magnetometry technique based on continuous-wave optically detected magnetic resonance (CW-ODMR) measurements, which enables the detection of signals in the hundred-MHz range. By applying a strong static magnetic field transverse to the NV axis, the energy separation between the relevant electron-spin states was tuned and resonantly coupled with the target radiofrequency (RF) magnetic field, thereby forming RF-dressed states. Unlike pulsed dynamical-decoupling schemes, this approach does not require high-power microwave pulse sequences. The key feature of our method is that the detectable frequency can be tuned by controlling the bias magnetic field strength. Using this methodology, we have experimentally achieved the frequency-tunable detection of AC magnetic fields from 14.4-632 MHz. The sensitivity was 0.558 uT/Hz^(0.5) at 14.4 MHz and 24.4 uT/Hz^(0.5) at 632 MHz. We characterized the field-dependent ODMR contrast and linewidth, and found that their degradation at large transverse fields is a important factor limiting the high-frequency sensitivity. These results establish a simple CW-ODMR approach for widely tunable RF magnetic-field sensing without high-power pulsed spin control.
Magnetometry with nitrogen-vacancy (NV) centers in diamond has so far been measured via emission of light from NV centers or via absorption at the singlet transition at 1042 nm. Here, we demonstrate a phenomenon of broadband optical absorption by the NV centers starting in the emission wavelength and reaching up to 1000 nm. The measurements are enabled by a high-finesse cavity, which is used for room-temperature continuous wave pump-probe experiments. The red to infrared probe beam shows the typical optically detected magnetic resonance (ODMR) signal of the NV spin with contrasts up to 42 %. This broadband optical absorption has not yet been reported in terms of NV magnetometry. We argue that the lower level of the absorbing transition could be the energetically lower NV singlet state, based on the increased optical absorption for a resonant microwave field and the spectral behavior. Investigations of the photon-shot-noise-limited sensitivity show improvements with increasing probe wavelength, reaching an optimum of 7.5pT/Hz. The results show significantly improved ODMR contrast compared to emission-based magnetometry. This opens a new detection wavelength regime with coherent laser signal detection for high-sensitivity NV magnetometry.
The Nitrogen-Vacancy (NV) center in diamond is a prominent quantum system leveraged for advanced quantum metrology, particularly in high-precision magnetometry and high-resolution quantum imaging, exploiting the Optically Detected Magnetic Resonance (ODMR) spectroscopy technique. Proper radio-frequency (RF) excitation of NV centers is critical in order to manipulate these quantum states effectively. Our research focuses on optimizing the continuous-wave RF excitation of ensembles of NV centers on coplanar waveguide transmission lines (CPW-TL), measuring the centers' photoluminescence (PL) signal as a function of RF power. This setup enhances the sensitivity and resolution of the NV center PL signal. By combining CPW-TL lines with nanodiamonds, our approach aims to develop a scalable and tunable platform that can be deployed in a variety of quantum sensing scenarios, including in biomedical applications, navigation systems, environmental monitorlng, and beyond.
Nitrogen Vacancy (NV) centers are point defects in diamond that allow magnetic field sensing based on Optically Detected Magnetic Resonance (ODMR). They are processed in ultrapure single-domain CVD grown diamond crystals and can be operated at room temperature. This results in solid-state sensors with a wide variety of applications. Ensemble of NV centers can be used to perform wide-field magnetic imaging with sensitivity in the nT range. Single NV centers can also be processed, which allows sensing at the atomic scale. This possibility, combined with its unique coherence properties, make NV center an ideal candidate for quantum sensing.
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.