Noise Suppression of Nitrogen-Vacancy Magnetometer in Lock-In Detection Method by Using Common Mode Rejection

At a Glance

Metadata	Details
Publication Date	2023-09-24
Journal	Micromachines
Authors	Yang Li, Doudou Zheng, Zhenhua Liu, Hui Wang, Yankang Liu
Institutions	North University of China, The University of Osaka
Citations	8
Analysis	Full AI Review Included

Executive Summary

This research details the implementation and optimization of a Common Mode Rejection (CMR) technique to significantly enhance the performance metrics of Nitrogen-Vacancy (NV) center magnetometers operating in the lock-in detection mode.

Core Value Proposition: A CMR model was established to effectively suppress laser fluctuation noise, which typically limits the magnetic field resolution when high laser power is used to achieve wide bandwidth.
Resolution Achievement: The detection magnetic field resolution was dramatically improved by a factor of nearly 5.7, increasing from 4.49 nT/Hz^1/2 to 790.8 pT/Hz^1/2.
Noise Suppression: Simulation results demonstrated a 6.2 times reduction in the noise level of the light-detected magnetic resonance (ODMR) signal variance after applying CMR. Experimental testing confirmed a 5.5 times reduction in the standard deviation (σ_β) of the step response signal noise.
Bandwidth Optimization: Through optimization of laser power (460 mW) and modulation frequency (600 Hz), the system achieved an optimal -3 dB detection bandwidth of 75 Hz, representing a five-fold enhancement over previous work by the research group.
Dynamic Range: The system exhibits an inherent magnetic field dynamic range of 392.857 µT (±196.429 µT).
Application Suitability: The resulting wide-bandwidth, high-resolution NV magnetic sensor is suitable for demanding applications such as power system monitoring, geomagnetic navigation, and current transformers.

Technical Specifications

Parameter	Value	Unit	Context
Magnetic Field Resolution (After CMR)	790.8	pT/Hz^1/2	Optimized system performance
Magnetic Field Resolution (Before CMR)	4.49	nT/Hz^1/2	Baseline performance
Resolution Improvement Factor	5.7	times	Enhancement via CMR
Detection Bandwidth (-3 dB)	75	Hz	Optimal setting
Optimal Laser Power	460	mW	For maximum bandwidth
Optimal Modulation Frequency	600	Hz	For maximum bandwidth
Dynamic Range (Total)	392.857	µT	Measurement range
Photon Shot Noise Limit	3.34	nT/Hz^1/2	Theoretical limit
ODMR FWHM (Δν)	10.5	MHz	Full Width at Half Maximum
Resonant Signal Contrast (C)	0.08	-	Measured system contrast
Gyromagnetic Ratio (γ)	2.8	MHz/Gs	NV center constant
Diamond Type	HPHT	-	High-Pressure High-Temperature
Diamond Dimensions	3 x 2.5 x 1	mm³	Sample size
Initial Nitrogen Concentration	100	ppm	Before processing
Final NV Concentration	3.32	ppm	After processing

Key Methodologies

The experimental methodology focused on sample preparation, the implementation of the Common Mode Rejection (CMR) technique, and subsequent system optimization.

Diamond Sample Preparation:
- The diamond sample was produced using the High-Pressure High-Temperature (HPHT) method, featuring a nitrogen concentration of 100 ppm and a <110> surface polishing direction.
- NV centers were created by exposing the sample to 10 MeV electron irradiation for 4 hours.
- The sample was subsequently annealed at 850 °C for 2 hours, resulting in a final NV concentration of approximately 3.32 ppm.
Common Mode Rejection (CMR) Implementation:
- A balanced photodetector (PD) was utilized to perform signal subtraction.
- The 532 nm excitation laser beam was split using a polarizing beam splitter (PBS).
- The signal path focused the laser onto the diamond surface (via a 60x objective lens) to excite the NV centers, and the resulting red fluorescence (600-800 nm) was guided to the signal end of the PD through a long-pass filter.
- The reference path directed the remaining portion of the laser beam to the reference end of the PD, counteracting the laser intensity noise.
- Precise adjustment of the attenuator in the reference path was critical to ensure the variances of the two signals were closely matched, enabling optimal noise cancellation via subtraction.
ODMR and Lock-In Detection:
- A uniform magnetic field (1.5 mT) was applied using a three-axis Helmholtz coil.
- The microwave source frequency was fixed at the maximum slope point of the ODMR signal for optimal linearity and resolution.
- A low-frequency modulation signal (f_ref = 500 Hz, f_Dev = 1 MHz) was applied to the microwave signal.
- The demodulated signal was detected using a lock-in amplifier (LIA) to extract the magnetic field information.
System Optimization:
- The system bandwidth was tested by applying an alternating magnetic field (1-1000 Hz) and measuring the normalized amplitude response.
- The optimal operating parameters were determined to be 460 mW laser power and 600 Hz modulation frequency, yielding the maximum -3 dB bandwidth of 75 Hz.

Commercial Applications

The wide-bandwidth, high-magnetic field resolution achieved by this CMR-enhanced NV magnetometer makes it highly suitable for applications requiring both speed and precision.

Power Systems: Monitoring and sensing currents in high-power infrastructure, potentially replacing traditional current transformers.
Geomagnetic Navigation: High-resolution vector magnetometry for calibrating and navigating based on geomagnetic anomalies.
Diamond NV Color Center Current Transformers: High-accuracy, long-term stable current sensing, particularly for electric vehicle battery monitoring.
Quantum Sensing Platforms: Provides a reference methodology for improving the performance of other solid-state quantum sensors, including:
- Electric field sensors
- Acceleration sensors
Medical and Bioimaging: Potential use in highly sensitive magnetic measurements, such as magnetocardiography (measuring cardiac magnetic signals).

View Original Abstract

Nitrogen-vacancy (NV) centers in diamonds are promising solid-state magnetic sensors with potential applications in power systems, geomagnetic navigation, and diamond NV color center current transformers, in which both high bandwidth and high magnetic field resolution are required. The wide bandwidth requirement often necessitates high laser power, but this induces significant laser fluctuation noise that affects the detection magnetic field resolution severely. Therefore, enhancement of the magnetic field resolution of wide-bandwidth NV center magnetic sensors is highly important because of the reciprocal effects of the bandwidth and magnetic field resolution. In this article, we develop a common mode rejection (CMR) model to eliminate the laser noise effectively. The simulation results show that the noise level of the light-detected magnetic resonance signal is significantly reduced by a factor of 6.2 after applying the CMR technique. After optimization of the laser power and modulation frequency parameters, the optimal system bandwidth was found to be 75 Hz. Simultaneously, the system’s detection magnetic field resolution was enhanced significantly, increasing from 4.49 nT/Hz1/2 to 790.8 pT/Hz1/2, which represents an improvement of nearly 5.7 times. This wide-bandwidth, high-magnetic field resolution NV color center magnetic sensor will have applications including power systems, geomagnetic navigation, and diamond NV color center current transformers.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi14101823

References

2021 - A hybrid magnetometer towards femtotesla sensitivity under ambient conditions [Crossref]
2020 - Vector Electrometry in a Wide-Gap-Semiconductor Device Using a Spin-Ensemble Quantum Sensor [Crossref]
2018 - Precise temperature sensing with nanoscale thermal sensors based on diamond NV centers [Crossref]
2017 - Optimised frequency modulation for continuous-wave optical magnetic resonance sensing using nitrogen-vacancy ensembles [Crossref]
2014 - Nitrogen-Vacancy color center in diamond—Emerging nanoscale applications in bioimaging and biosensing [Crossref]
2019 - Dynamically Polarizing Spin Register of N-V Centers in Diamond Using Chopped Laser Pulses [Crossref]
2013 - Diamond NV centers for quantum computing and quantum networks [Crossref]
2022 - High-precision robust monitoring of charge/discharge current over a wide dynamic range for electric vehicle batteries using diamond quantum sensors [Crossref]