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ACS Photonics

Microfabricated Active Laser Noise Suppression Device for a High-Sensitivity Diamond Quantum Magnetometer

Nan Wang, Yichen Liu, Yongquan Su, Xiao Peng, Yuqiang Hu, Qihui Liu, Fei Xie, Yaochen Zhu, Xin Chen, Xin Luo, Yonggui Zhang, Lihao Wang, Maoheng Jing, Chun Li, Shaoxiong Nie, Hao Chen, Zhenyu Wu, Jiangong Cheng

Published Jan 18, 2025• 5 citations
Publisher

Abstract

Nitrogen vacancy (NV) centers in diamonds have emerged as one of the most promising candidates for magnetic field sensing. However, the laser intensity fluctuation is coupled to the diamond fluorescence; thus, the sensitivity is severely affected by the noise and stability of the laser. Integrating both the diamond quantum sensor and laser noise suppression device is a crucial step toward miniaturization and practical applications. Here, we present a piezoelectric-driven device to dynamically adjust the laser noise cancelation with dimensions of 5 × 5 × 1.5 mm 3 based on a grating interferometer. This device incorporates a grating structure to produce diffracted reference light with high-accuracy intensity modulation, actively tracking the fluorescence signal for differential common-mode rejection (CMR), effectively eliminating laser noise in the system, whereby the sensitivity of magnetic field detection is increased by a factor of 34, reaching 160 pT · Hz –1/2, and beneficial to the long-term stability. The compact design of this laser noise suppressor, in combination with a miniaturized diamond magnetometer, demonstrates its potential for high-precision magnetic field detection ability and strong portability.

DOI
10.1021/acsphotonics.4c01825

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Nitrogen vacancy (NV) centers in diamonds have emerged as one of the most promising candidates for magnetic field sensing. However, the laser intensity fluctuation is coupled to the diamond fluorescence; thus, the sensitivity is severely affected by the noise and stability of the laser. Integrating both the diamond quantum sensor and laser noise suppression device is a crucial step toward miniaturization and practical applications. Here, we present a piezoelectric-driven device to dynamically adjust the laser noise cancelation with dimensions of 5 × 5 × 1.5 mm 3 based on a grating interferometer. This device incorporates a grating structure to produce diffracted reference light with high-accuracy intensity modulation, actively tracking the fluorescence signal for differential common-mode rejection (CMR), effectively eliminating laser noise in the system, whereby the sensitivity of magnetic field detection is increased by a factor of 34, reaching 160 pT · Hz –1/2, and beneficial to the long-term stability. The compact design of this laser noise suppressor, in combination with a miniaturized diamond magnetometer, demonstrates its potential for high-precision magnetic field detection ability and strong portability.
Abstract We present a miniaturized diamond quantum sensor integrated with a real-time laser noise suppression module, ensuring reliable operation for high-precision magnetic field measurements in the long-run. A piezoelectric micro-electromechanical systems mirror based variable optical attenuator (VOA) is constructed with an attenuation range of −3 dB to −20 dB. The VOA is employed to dynamically adjusts the intensity of reference laser signal to actively track diamond fluorescence signal and the laser noise is suppressed, whereby a sensitivity of 211 pT·Hz −1/2 is achieved. For real-time fluorescence tracking, a closed-loop control system is implemented to maintain functional common-mode rejection (CMR). Compared with passive CMR configuration (open-loop), the dynamic magnetic field noise of the closed-loop diamond sensor is reduced by 1.6 times in both challenging scenarios, including laser power fluctuations and strong magnetic fields. Furthermore, an optimal sensitivity is effectively maintained in a 2 h measurement time. Compared with open-loop operation, the sensitivity fluctuation of the closed-loop system is reduced by a factor of 14.29. The fluorescence tracking scheme provides an effective approach to enhancing the operational stability for practical magnetic sensing applications.
The nitrogen–vacancy center in diamond enables highly sensitive magnetic-field measurements. In this work, we demonstrate an excellent sensitivity of 7.9 pT·Hz –1/2 in the near-DC range of 1 to 1000 Hz. This performance is achieved using a 35 mW laser power and 1 mW microwave power enabled by 561 nm laser excitation and the resonant-antenna design. By leveraging dual resonance with intrinsic π shift for real-time common-mode rejection, this technique effectively suppresses low-frequency noise and pushes the 1/ f corner frequency down to 1 Hz, with a measured sensitivity at 1 Hz of 10.6 pT·Hz –1/2 . The magnetometer also exhibits excellent capability in detecting magnetic anomalies, promoting the practical use of diamond quantum sensors in biomedical, geophysical, and other real-world applications.
Ensemble nitrogen-vacancy (NV) diamond magnetometers combine high sensitivity with vector-field reconstruction, but practical deployment is limited by errors arising from high-frequency laser noise during short-duration operations and slow-varying gain fluctuations and offset drift during long-term operation. Here, we present an integrated digital architecture for achieving NV magnetometry stability across distinct timescales. A dynamic differential readout continuously balances fluorescence and reference channels to suppress correlated laser noise. Second-derivative Lorentzian lineshape tracking enables in-situ correction of slope variations arising from slow changes in gain and optical excitation. We further identify temperature-induced bias-magnet fluctuations as a dominant source of long-term drift and introduce a magnetic eigenvector transformation that uses the intrinsic response of NV resonances to eliminate these variations. We show, under unshielded ambient conditions, that this architecture achieves an off-resonance noise factor of 1.0 ±\pm± 0.1, matching the fundamental limit with ten-fold suppression of long-term drift, enabling stable, field-ready quantum magnetometry.
In this study, we developed a diamond quantum magnetometer based on Ramsey interferometry with a short sensor-to-sample distance. Conventional biomagnetic sensors with ensemble nitrogen-vacancy centers using continuous-wave optically detected magnetic resonance and Ramsey methods typically rely on watt-level lasers to achieve high sensitivity, resulting in thermal issues. In contrast, by employing the light-trapping diamond waveguide technique in a high-pressure and high-temperature diamond sample treated with electron beam irradiation, we obtained a high photon conversion efficiency of 9.5%, enabling us to simultaneously achieve a high sensitivity of 2.93(7) pT/Hz^1/2 in the 100-400 Hz frequency range and a minimal temperature increase of only approximately 13 K at a low laser power of 210 mW. Using a dry phantom designed to mimic magnetoencephalography signals, we measured a weak magnetic field of 77.7(2) pT without signal averaging at a sensor-to-sample distance of 2.5 mm. This short-distance measurement prevents severe spatial signal attenuation, yielding a high signal-to-noise ratio. The development here is crucial for practical biomagnetic applications based on Ramsey interferometry.
Diamond quantum sensors utilizing nitrogen-vacancy (NV) centers in diamond can measure a tiny magnetic-field variation at room temperature with a high linearity and high spatial resolution. Because of these advantages, they have been actively studied for application to measure a biomagnetic field. In biomagnetic sensing applications, it is effective to measure at multiple points simultaneously with high sensitivity. In this study, we developed a highly sensitive diamond quantum sensor that can simultaneously measure the magnetic field at two points at the millimeter interval. We used two diamonds that were split from one HPHT-grown diamond and placed them at the 3-mm interval. A laser-induced fluorescence from the two diamonds were detected by a single photodiode. We applied different bias magnetic fields to each diamond, and thus the magnetic resonances at these diamonds had different resonance frequencies. By applying microwave fields whose frequencies were modulated at different modulation frequencies, the magnetic fields at the two diamonds can be obtained independently after demodulation. The noise spectral densities in the magnetic field measurement at the two diamonds’ locations. Since the measurement was performed outside a magnetic shield, a severe low-frequency environmental noise from railways and power line (50 Hz) noise peaks were observed. We evaluated the field sensitivities at the two diamonds to be 22 pT/√Hz in 25-300 Hz range with neglecting the power-line noise peaks and the environment noise peaks. The capability of simultaneously measuring a magnetic field at two points with the such high sensitivities will facilitate the biomagnetic sensing applications.
Abstract The negatively charged nitrogen vacancy (NV) color center in diamond is a type of point defect, which is extensively studied as a promising high‐sensitivity solid‐state magnetic field sensor. However, its transition from research to application is still limited due to the technical challenges of an integrated physical package. Here, an integrated diamond sensor is demonstrated with the essential component on the order of mm 3 , which is realized by a standard microfabrication process. A microfabrication‐compatible light guiding structure is constructed, providing photon detection efficiency of 66% and thus enabling a magnetic field detection sensitivity reaching 203 pT·Hz 1/2 . Incorporation of the sensor device with a magnetic yoke enables high‐precision wide‐range direct‐current sensing with current isolation. A current measuring range of 0–400 A with a minimum detection limit of 2 mA is achieved. By utilizing dual spin resonance modulation, the temperature drift is suppressed from 219 to 1.92 ppm∙°C −1 . This configuration provides new possibilities as a robust and scalable platform for current quantum sensing technologies.