Picotesla magnetometry of microwave fields with diamond sensors

At a Glance

Metadata	Details
Publication Date	2022-08-10
Journal	Science Advances
Authors	Zhecheng Wang, Fei Kong, Pengju Zhao, Zhehua Huang, Pei Yu
Institutions	University of Science and Technology of China, Suzhou University of Science and Technology
Citations	74
Analysis	Full AI Review Included

Technical Documentation: Picotesla Microwave Magnetometry using NV Diamond Sensors

This document analyzes the research paper “Picotesla magnetometry of microwave fields with diamond sensors” (arXiv:2206.08533v2) and outlines how 6CCVD’s advanced MPCVD diamond materials and customization capabilities can support the replication, optimization, and scaling of this quantum sensing technology.

Executive Summary

This research successfully demonstrates a highly sensitive, robust method for detecting weak microwave magnetic fields using Nitrogen-Vacancy (NV) ensembles in high-purity diamond.

Ultra-High Sensitivity: Achieved a record sensitivity of 8.9 pT·Hz^-1/2 for 2.9 GHz microwave fields, significantly advancing high-frequency magnetometry.
Novel Detection Scheme: Utilizes continuous heterodyne detection, which eliminates the need for complex, power-limited pulsed spin control sequences, simplifying the experimental setup and enabling scalability.
Picotesla Detection: Demonstrated linear response to weak microwave fields across a dynamic range spanning five orders of magnitude (1 pT to 100 nT), with a minimum detectable field of 0.28 pT in 1000 s.
Exceptional Resolution: Achieved frequency resolution scaling as 1/t, reaching 0.1 mHz over a 10000 s measurement time.
Material Requirement: Performance relies critically on high-quality, 100-oriented MPCVD diamond with 99.99% ¹²C isotopic purity and a controlled, highly-doped NV layer (~4 ppm).
Scalability Potential: The authors note that the method is directly applicable to larger diamond sensors, offering a clear path to achieving femtotesla (fT) sensitivity levels.

Technical Specifications

The following hard data points were extracted from the experimental results and material parameters:

Parameter	Value	Unit	Context
Microwave Field Sensitivity	8.9	pT·Hz^-1/2	Achieved at 2.9 GHz
Minimum Detectable Field (b₁)	0.28	pT	Total measurement time t = 1000 s
Frequency Resolution	0.1	mHz	Total measurement time t = 10000 s
ODMR Linewidth (FWHM, Δν)	482	kHz	Measured at 365 nT MW field
NV Center Density (n_NV)	~4	ppm	Estimated NV density
Total NV Centers (N_NV)	~2.8 x 10¹³	Centers	Within effective sensor volume
Effective Sensor Volume	4 x 10^-2	mm³	Volume of the diamond sensor
Diamond Isotopic Purity	99.99%	¹²C	Required for long coherence times
Zero-Field Splitting (D)	2.87	GHz	NV ground state triplet
Reference MW Strength (B₁)	~200	nT	Required for heterodyne detection
Dynamic Range (Linear Response)	1 pT to 100 nT	T	5 orders of magnitude

Key Methodologies

The experiment relies on precise material engineering and a simplified optical detection scheme:

Material Selection: A 100-oriented MPCVD diamond was used, featuring 99.99% ¹²C isotopic purity to minimize magnetic noise from nuclear spins (enhancing T₂). A highly-doped layer (~10 µm thick) was grown to achieve a high NV density (~4 ppm).
Optical Setup: A 532 nm high-power laser was used for continuous illumination and NV spin polarization. Fluorescence was collected using an optical compound parabolic concentrator (CPC) to maximize collection efficiency.
Microwave Generation: Two independent RF signal generators were used to create the weak signal microwave (b₁) and the moderate, slightly detuned reference microwave (B₁). These were amplified and radiated via a 5-mm-diameter loop antenna.
Magnetic Field Application: A static external magnetic field (B ~ 12.5 G) was applied perpendicular to the diamond surface to lift the degeneracy of the NV spin states (Zeeman splitting).
Heterodyne Detection: The signal and reference microwaves interfere, resulting in an oscillation of the NV photoluminescence at the beat frequency ($\delta$). This AC signal is linearly proportional to the signal field strength (b₁).
Signal Processing: The photovoltage was detected by a photodiode, amplified differentially, and analyzed via Fourier transform spectroscopy to extract the signal amplitude and frequency, providing the field strength and frequency resolution.

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials required to replicate and significantly extend this picotesla magnetometry research. Our capabilities directly address the critical material specifications needed for high-performance quantum sensors.

Applicable Materials and Customization

Research Requirement	6CCVD Solution & Capability	Technical Advantage
High Isotopic Purity (99.99% ¹²C)	Optical Grade SCD Wafers (Isotopically Enriched)	We provide Single Crystal Diamond (SCD) with custom ¹²C enrichment levels (e.g., 99.99% or higher). This is essential for maximizing the NV center coherence time (T₂), which directly dictates the achievable magnetic sensitivity.
Controlled High NV Density	Custom Doping Profiles (SCD)	We specialize in precise nitrogen incorporation during MPCVD growth. We can engineer the required structure: a thin, highly-doped layer (high NV density) grown on a low-strain, high-purity SCD substrate, optimizing the signal-to-noise ratio (SNR).
Scalability to Larger Sensors	Custom Dimensions up to 125 mm (PCD)	The paper notes that sensitivity scales with sensor volume. 6CCVD offers large-area Polycrystalline Diamond (PCD) plates up to 125 mm, or large SCD plates, enabling direct scaling to achieve fT-level sensitivity for applications like radio astronomy or radar.
Specific Crystal Orientation	SCD Substrates (100, 110, 111)	We routinely supply high-quality SCD substrates in the required 100 orientation, ensuring optimal alignment of the NV centers relative to the applied magnetic field and microwave antenna.
Surface Quality for Optical Integration	Precision Polishing (Ra < 1 nm)	Our SCD polishing achieves surface roughness (Ra) < 1 nm. This minimizes scattering losses, crucial for maximizing the fluorescence collection efficiency utilized by the CPC setup.
On-Chip Device Integration	Custom Metalization Services	For future integration of on-chip antennas or waveguides (e.g., Ti/Pt/Au, Cu), 6CCVD offers in-house metalization capabilities, streamlining the fabrication of complex diamond quantum devices.

Engineering Support

6CCVD’s in-house PhD team provides expert consultation on material selection and growth recipes for advanced quantum sensing projects. We assist engineers and scientists in balancing the trade-offs between NV density, isotopic purity, and substrate thickness (SCD: 0.1 µm - 500 µm) to optimize performance for specific microwave magnetometry or quantum computing applications.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Developing robust microwave-field sensors is both fundamentally and practically important with a wide range of applications from astronomy to communication engineering. The nitrogen vacancy (NV) center in diamond is an attractive candidate for such purpose because of its magnetometric sensitivity, stability, and compatibility with ambient conditions. However, the existing NV center-based magnetometers have limited sensitivity in the microwave band. Here, we present a continuous heterodyne detection scheme that can enhance the sensor’s response to weak microwaves, even in the absence of spin controls. Experimentally, we achieve a sensitivity of 8.9 pT Hz −1/2 for microwaves of 2.9 GHz by simultaneously using an ensemble of n NV ~ 2.8 × 10 13 NV centers within a sensor volume of 4 × 10 −2 mm 3 . Besides, we also achieve 1/ t scaling of frequency resolution up to measurement time t of 10,000 s. Our scheme removes control pulses and thus will greatly benefit practical applications of diamond-based microwave sensors.

Tech Support

Original Source

DOI: https://doi.org/10.1126/sciadv.abq8158