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

Technical Documentation & Analysis: Wide-Bandwidth NV Magnetometry via Common Mode Rejection

Executive Summary

This document analyzes the research demonstrating significant noise suppression in wide-bandwidth Nitrogen-Vacancy (NV) center magnetometers using a Common Mode Rejection (CMR) technique. The findings are highly relevant for engineers requiring high-resolution magnetic sensing in dynamic environments.

Core Achievement: Successful implementation of a Common Mode Rejection (CMR) model to effectively eliminate high-frequency laser fluctuation noise, a critical limiting factor in high-power, wide-bandwidth NV sensing.
Resolution Enhancement: The system’s magnetic field resolution was dramatically improved by a factor of nearly 5.7 times, moving from 4.49 nT/Hz^1/2 to an optimized 790.8 pT/Hz^1/2.
Bandwidth Optimization: Despite the typical trade-off between resolution and bandwidth, the system achieved an optimal detection bandwidth of 75 Hz, representing a five-fold enhancement over previous work by the research group.
Noise Reduction: Simulation confirmed the noise level variance of the light-detected magnetic resonance (ODMR) signal was reduced by a factor of 6.2 after applying CMR.
Material Requirement: The experiment utilized a high-quality, irradiated, and annealed diamond sample with a controlled NV concentration (3.32 ppm), emphasizing the need for precision-engineered SCD material.
Target Applications: The resulting wide-bandwidth, high-resolution sensor is ideal for power systems monitoring, geomagnetic navigation, and diamond NV color center current transformers.

Technical Specifications

Parameter	Value	Unit	Context
Optimized Magnetic Field Resolution	790.8	pT/Hz^1/2	After CMR implementation
Initial Magnetic Field Resolution	4.49	nT/Hz^1/2	Before CMR implementation
Resolution Improvement Factor	5.7	Times	Enhancement achieved via CMR
Optimal System Bandwidth (-3 dB)	75	Hz	Achieved at optimal laser power and modulation frequency
Noise Variance Reduction (Simulation)	6.2	Factor	Reduction in ODMR signal noise level
Noise Standard Deviation Reduction (Step Signal)	5.5	Factor	Reduced from 312 nT to 57 nT
Optimal Laser Power	460	mW	Power setting maximizing -3 dB bandwidth
Optimal Modulation Frequency	600	Hz	Frequency setting maximizing -3 dB bandwidth
ODMR Full Width at Half Maximum (FWHM, Δν)	10.5	MHz	Used in resolution calculation
Resonant Signal Contrast (C)	0.08	Dimensionless	Used in resolution calculation
Electron Spin Gyromagnetic Ratio (γ)	2.8	MHz/Gs	NV center constant
Inherent Dynamic Range	±196.429	µT	Measurement range for the magnetic field
Diamond Sample Dimensions	3 x 2.5 x 1	mm³	HPHT material used in the experiment
NV Concentration (Resulting)	3.32	ppm	After irradiation and annealing

Key Methodologies

The experiment relied on precise material engineering and optimization of the lock-in detection parameters combined with the novel CMR technique.

Material Selection and Preparation:
- Diamond was produced via the High-Pressure High-Temperature (HPHT) method.
- Initial Nitrogen concentration was 100 ppm.
- Surface polishing direction was <110>.
- The sample underwent 10 MeV electron irradiation for 4 hours.
- Post-irradiation annealing was performed at 850 °C for 2 hours to activate NV centers, resulting in a 3.32 ppm NV concentration.
Optical and Microwave Setup:
- A 532 nm laser (up to 10,000 mW) was used for NV center excitation.
- The laser beam was split using a Polarizing Beam Splitter (PBS). One portion excited the diamond via a 60× objective lens (NA = 0.9). The other portion was directed to the reference end of a balanced photodetector (PD).
- Red fluorescence (600-800 nm) was collected and guided to the signal end of the balanced PD via a long-pass filter.
- A three-axis Helmholtz coil generated the uniform magnetic field (1.5 mT) and the alternating magnetic field b(t) (1-1000 Hz).
Common Mode Rejection (CMR) Implementation:
- The CMR model was established to subtract the normalized signals from the PD signal port (fluorescence) and the reference port (laser intensity).
- Precise adjustment of the attenuator controlling the laser signal amplitude was critical to ensure the variances of the two signals were matched for optimal noise cancellation.
Signal Detection and Optimization:
- The ODMR signal was acquired, and a low-frequency modulation signal was applied to the microwave signal at the maximum slope point.
- Detection was performed using a Lock-In Amplifier (LIA, HF2LI 50 MHz).
- System performance was optimized by varying laser power (up to 780 mW) and modulation frequency (500 Hz to 1.1 kHz) to maximize the -3 dB bandwidth (achieved at 75 Hz).
- Magnetic field resolution was calculated using the noise amplitude spectral density (ASD) derived from the LIA output.

6CCVD Solutions & Capabilities

6CCVD provides the precision-engineered diamond materials necessary to replicate and advance this high-performance NV magnetometer research. Our expertise in MPCVD growth offers superior control over purity and defect incorporation compared to the HPHT material used in the study.

Applicable Materials

To achieve the high NV density (3.32 ppm) and optical quality required for this wide-bandwidth, high-resolution sensor, 6CCVD recommends:

Optical Grade Single Crystal Diamond (SCD):
- Purity: High-purity SCD (low intrinsic strain) is essential for maintaining narrow ODMR linewidths (FWHM = 10.5 MHz).
- Doping Control: We offer controlled nitrogen incorporation during MPCVD growth to achieve the target 100 ppm N concentration, ensuring uniform NV ensemble formation after post-processing.
- Surface Quality: SCD wafers with Ra < 1 nm polishing are available, minimizing scattering losses critical for efficient fluorescence collection and noise reduction.
Polycrystalline Diamond (PCD) (For Scalability):
- For applications requiring larger sensing areas or high-volume production (up to 125 mm wafers), high-quality PCD with controlled nitrogen doping can be supplied, offering a cost-effective alternative for ensemble sensing.

Customization Potential

The success of this research hinges on precise material dimensions and integration capabilities, which are core strengths of 6CCVD.

Research Requirement	6CCVD Customization Capability	Value Proposition
Custom Dimensions (3 x 2.5 x 1 mm³)	Custom laser cutting and dicing services for plates up to 125 mm (PCD) or large SCD wafers.	Provides exact form factors needed for integration into complex optical/MW setups.
Controlled NV Formation (Irradiation/Annealing)	We supply pre-processed SCD/PCD material, including controlled electron irradiation and high-temperature annealing (e.g., 850 °C), to guarantee the required 3.32 ppm NV concentration.	Ensures consistent, high-performance NV ensemble density for optimal contrast (C = 0.08).
Integrated Antenna Structures	Internal metalization services (Au, Pt, Pd, Ti, W, Cu) for creating on-chip microwave (MW) antennas directly on the diamond surface.	Facilitates efficient MW delivery and integration, crucial for maximizing the demodulation signal slope (max dV/df = 0.708 mV/MHz).
Thickness Control (1 mm substrate)	SCD thicknesses from 0.1 µm to 500 µm, and substrates up to 10 mm.	Allows researchers to optimize material volume for ensemble sensing while managing heat dissipation from high laser power (460 mW).

Engineering Support

6CCVD’s in-house team of PhD material scientists and quantum engineers specializes in optimizing diamond properties for quantum sensing. We can assist researchers in selecting the optimal nitrogen concentration, irradiation dose, and annealing recipe to maximize the magnetic field resolution (790.8 pT/Hz^1/2) and bandwidth (75 Hz) for similar NV Magnetometry projects. Our support ensures the material quality meets the stringent demands of noise-sensitive techniques like Common Mode Rejection.

Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We ship globally (DDU default, DDP available).

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]