Quantum magnetometer based on cross-relaxation resonances in ensembles of NV-centers in diamond

At a Glance

Metadata	Details
Publication Date	2022-01-01
Journal	Журнал технической физики
Authors	Р. А. Ахмеджанов, Л. А. Гущин, I. V. Zelensky, Kupaev A.V., В. А. Низов
Institutions	Institute of Applied Physics
Analysis	Full AI Review Included

Technical Documentation: Cross-Relaxation NV-Center Magnetometry

This document analyzes the research paper “Quantum magnetometer based on cross-relaxation resonances in ensembles of NV-centers in diamond” and outlines specific material solutions and capabilities offered by 6CCVD to replicate, optimize, and scale this advanced quantum sensing technology.

Executive Summary

This research successfully demonstrates a novel quantum magnetometer utilizing cross-relaxation (CR) resonances in Nitrogen-Vacancy (NV) ensembles, eliminating the need for traditional microwave (MW) radiation.

Core Achievement: Demonstrated a working magnetometer model achieving a magnetic field sensitivity of 18 nT/Hz^1/2 in the scalar measurement regime.
Methodology: The sensor relies on optically detected CR resonances observed when the magnetic field projections onto two groups of NV-center axes coincide.
Material Used: A synthetic HPHT diamond crystal (~300 µm thick) irradiated with 10¹⁸ electrons/cm² was used as the active element.
Key Advantage: The elimination of MW radiation simplifies the sensor design and expands applicability, particularly in environments sensitive to RF interference (e.g., biomedical research).
Optimization Path: The authors identify that sensitivity is currently limited by shot noise and suggest increasing NV concentration and utilizing isotopically pure ¹²C diamond to narrow resonances and increase contrast.
6CCVD Relevance: 6CCVD specializes in high-purity, isotopically enriched Single Crystal Diamond (SCD) and custom processing required to achieve optimal NV-center density and coherence for next-generation quantum magnetometers.

Technical Specifications

The following hard data points were extracted from the research paper detailing the sensor performance and material parameters.

Parameter	Value	Unit	Context
Achieved Sensitivity (Scalar)	18	nT/Hz^1/2	Average noise at frequencies > 0.6 Hz.
Theoretical Shot Noise Limit	10.7	nT/Hz^1/2	Maximum possible sensitivity for the current optical setup.
Sensor Material Type	Synthetic HPHT Diamond	N/A	Ensemble NV-centers.
Sensor Thickness	~300	µm	Crystal size used for the sensor model.
Electron Irradiation Dose	10¹⁸	electrons/cm²	Used for NV-center creation.
Annealing Temperature	800	°C	Post-irradiation thermal treatment.
Optimal Pump Intensity (Contrast)	100	W/cm²	Intensity corresponding to maximum CR contrast.
Stable Operating Intensity (Limit)	50	W/cm²	Limited by adhesive failure/overheating.
Lock-in Detection Frequency	0.75	kHz	Selected frequency for best sensitivity.
Bias Magnetic Field Range	2.5 - 3	mT	Required to resolve CR resonances.
Measurement Range (Vector Regime)	±200	µT	Measurement range for each projection.

Key Methodologies

The experimental setup focused on optimizing the NV-center ensemble properties and employing a balanced optical detection scheme combined with lock-in amplification.

Material Preparation: A synthetic HPHT diamond crystal was irradiated with a high electron beam intensity (10¹⁸ electrons/cm²) and subsequently annealed at 800 °C to maximize NV-center formation.
Sensor Assembly: The ~300 µm diamond crystal was glued (NOA63 adhesive) to the end face of a multimode optical fiber (200 µm core diameter, NA 0.5).
Optical Pumping: Excitation was provided by 520 nm or 532 nm lasers. Stable operation was limited to 50 W/cm² due to thermal constraints imposed by the adhesive.
Magnetic Field Generation: A solenoid provided the scanning magnetic field (B^sc), while two micro-coils generated a static bias magnetic field (B^dc) of 2.5-3 mT to split the CR resonances.
Fluorescence Detection: A balanced photodetector scheme was implemented to measure the spin-dependent fluorescence signal, significantly suppressing residual laser intensity noise.
Signal Processing: Lock-in detection was used, applying an alternating magnetic field component (0.5-10 kHz range) to measure the derivative of the fluorescence signal, thereby increasing measurement accuracy.
Measurement Regimes: The system demonstrated capability for both scalar (measuring the shift of the central resonance) and vector (measuring the shift of all five resonances) magnetic field determination.

6CCVD Solutions & Capabilities

6CCVD provides the high-specification MPCVD diamond materials and customization services necessary to overcome the limitations identified in this research (thermal management, NV concentration, and isotopic purity) and achieve the next level of sensitivity.

Research Requirement / Optimization Path	6CCVD Solution & Capability	Material Recommendation
Achieving Sub-10 nT/Hz^1/2 Sensitivity	Requires narrowing the cross-relaxation resonances by eliminating ¹³C nuclear spins, which demands isotopically pure diamond.	Optical Grade SCD (Isotopically Pure ¹²C). Guaranteed ¹²C enrichment (> 99.99%). Available in thicknesses from 0.1 µm to 500 µm, polished to Ra < 1 nm.
Scaling NV Concentration	The authors suggest increasing the NV concentration beyond 10¹⁸ e/cm² for higher contrast. 6CCVD provides high-purity SCD optimized for high-dose irradiation and subsequent annealing.	High-Purity SCD Substrates with controlled initial nitrogen content, designed for robust post-processing (irradiation and 800 °C annealing).
Thermal Management & High Pump Power	Operation was limited to 50 W/cm² due to adhesive failure. Higher pump power (> 100 W/cm²) requires superior heat sinking.	Custom Metalization Services. 6CCVD offers in-house deposition of Ti/Pt/Au or W/Cu layers on the non-sensing face for direct bonding/soldering, enabling robust thermal dissipation.
Custom Sensor Geometry	The sensor used a 300 µm thick crystal attached to a fiber. Precise geometry is critical for integration into advanced collection optics (e.g., parabolic condensers).	Custom Thickness and Dimensions. SCD plates available from 0.1 µm to 500 µm. We offer precision laser cutting and shaping services to match specific fiber diameters or optical components.
Large-Area Sensor Arrays	For applications requiring large-scale sensing or mapping, the use of large diamond wafers is necessary.	Polycrystalline Diamond (PCD) Wafers. Available up to 125 mm diameter, polished to Ra < 5 nm, suitable for ensemble NV-center magnetometry arrays.
Global Logistics	Global delivery of sensitive materials.	Global Shipping (DDU/DDP). Reliable, insured global logistics ensures materials arrive safely and promptly.

Engineering Support

6CCVD’s in-house PhD team specializes in the growth and post-processing of diamond materials for quantum applications. We offer consultation services to assist researchers in selecting the optimal material specifications (e.g., nitrogen doping level, isotopic purity, and thickness) required for high-sensitivity, cross-relaxation NV-center magnetometry projects.

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

View Original Abstract

We create a working model of a magnetometer of a new type that is based on using cross-relaxation resonances in ensembles of NV-centers in diamond. This type of magnetometer does not require microwave radiation. For a sensor made out of a 300 micron diamond we demonstrate the magnetic field sensitivity of around 18 nT/Hz 1/2 . Keywords: cross-relaxation, NV-center, quantum magnetometer.

Tech Support

Original Source

DOI: https://doi.org/10.21883/tp.2022.11.55183.138-22