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ACS Photonics

A Sub-10 pT·Hz –1/2 Diamond Quantum Sensor with 1/ f Noise Suppression Using 561 nm Laser Excitation

Xiao Peng, Qihui Liu, Chengyu Yang, Xiaolong Luo, Yuqiang Hu, Yuetong Jin, Changbao Xu, Mingyong Xin, Guofeng Zhang, Baifu Zhang, Zhenyu Wu, Hao Chen

Published Mar 24, 2026• 3 citations
Publisher

Abstract

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.

DOI
10.1021/acsphotonics.6c00035

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ACS Photonics•Jan 18, 2025•5 citations
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.
Quantum sensing of low-frequency magnetic fields using nitrogen-vacancy (NV) center ensembles has been demonstrated in multiple experiments with sensitivities as low as $\sim1pT/1 pT/1pT/\sqrt{\text{Hz}}.Todate,however,demonstrationsofhigh−frequencymagnetometryintheGHzregimewithNVdiamondareordersofmagnitudelesssensitive,abovethenT/. To date, however, demonstrations of high-frequency magnetometry in the GHz regime with NV diamond are orders of magnitude less sensitive, above the nT/.Todate,however,demonstrationsofhigh−frequencymagnetometryintheGHzregimewithNVdiamondareordersofmagnitudelesssensitive,abovethenT/\sqrt{\text{Hz}}$ level. Here we adapt for microwave frequencies techniques that have enabled high-performance, low-frequency quantum sensors. Using a custom-grown NV-enriched diamond combined with a noise cancellation scheme designed for high-frequency sensing, we demonstrate a Rabi-sequence-based magnetometer able to detect microwave fields near 2.87 GHz with a record sensitivity of 3.4 pT/Hz\sqrt{\textrm{Hz}}Hz​. We demonstrate both amplitude and phase sensing and project tunability over a 300 MHz frequency range. This result increases the viability of NV ensembles to serve as microwave circuitry imagers and near-field probes of antennas.
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.
Nitrogen-vacancy (NV) color centers in diamond are promising solid-state quantum sensors working at room temperature. The number of NV centers limits the magnetic sensitivity of the quantum magnetometer. Increasing the number of NV centers is a challenging task due to technical issues such as microwave power density, detection noise.Here, we developed the sensor system with a large detection volume which contains a lot of NV centers. The microwave circuit enhances microwave power density. Digital filter with frequency modulation of microwave allows us to detect the magnetic field with low noise. Consequently, we obtained a DC magnetic field sensitivity of 980 pT/√Hz.This work was supported by MEXT Quantum Leap Flagship Program (MEXT Q-LEAP) Grant Number JPMXS0118067395.
While photoelectric detection of magnetic resonance (PDMR) can be applied to miniaturize nitrogen-vacancy (NV) center-based quantum sensors, real demonstration of PDMR-based magnetic field sensing remains as a distinctive challenge. To tackle this challenge, in this article, we fabricate diamond samples with electrodes and microwave antenna on the surface, and realize PDMR by detecting photocurrent in picoampere range via various lock-in amplifying modes. We obtain a theoretical and experimental sensitivity 397 nT/Hz and 921 nT/Hz of magnetic field detection in DC-10 Hz range with a laser intensity and microwave frequency modulation mode, respectively, and demonstrate for the first time, a real-time tracking of alternating magnetic field with a standard deviation of 1.5 uT. Furthermore, we investigate systematically the dependence of the PDMR contrast, linewidth and the sensitivity on the laser and microwave power, and find a perfect agreement with a master equation-based theory. Thus, our results represent a critical step forward in transitioning PDMR from a spectroscopic technique to a practical sensing modality.
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.