Multiplexed Sensing of Magnetic Field and Temperature in Real Time Using a Nitrogen-Vacancy Ensemble in Diamond

At a Glance

Metadata	Details
Publication Date	2022-01-07
Journal	Physical Review Applied
Authors	Jeong Hyun Shim, Seong-Joo Lee, Santosh Ghimire, Ju Il Hwang, Kwang-Geol Lee
Institutions	Korea Research Institute of Standards and Science, Chungbuk National University
Citations	43
Analysis	Full AI Review Included

Technical Documentation & Analysis: Multiplexed NV Diamond Sensing

Executive Summary

This research successfully demonstrates real-time, simultaneous multiplexed sensing of magnetic field and temperature using Nitrogen-Vacancy (NV) spin ensembles in diamond. The methodology and results validate the critical role of high-quality diamond materials and advanced optical/microwave engineering in next-generation quantum sensing applications.

Core Achievement: Real-time, concurrent measurement of magnetic field and temperature using a single NV diamond ensemble.
Methodology: Utilized Frequency-Division Multiplexing (FDM) via dual microwave driving (5 kHz and 7 kHz references) coupled with lock-in detection and digital signal processing.
High Sensitivity: Achieved magnetic field sensitivity of 70 pT/√Hz and temperature sensitivity of 25 µK/√Hz simultaneously.
Signal Isolation: Demonstrated a high isolation factor of 34 dB in the thermometry signal against magnetic field fluctuations, crucial for reliable multiplexing.
Material Requirement: The experiment relied on a Type 1b HPHT diamond (3 x 3 x 0.3 mm³) with a specific NV^- concentration (0.5 ppm) created via electron irradiation and annealing.
Optical Optimization: Enhanced photon collection efficiency to 56% using a high-refractive index half-ball lens (n ≈ 2.0) and an elliptic reflector, directly improving shot-noise limited performance.
Application Potential: The technique is highly applicable for dynamic environments, including operando monitoring of chemical reactions and in-vitro biological sensing.

Technical Specifications

The following hard data points were extracted from the research, highlighting the performance metrics and material requirements.

Parameter	Value	Unit	Context
Magnetic Field Sensitivity (η_B)	70	pT/√Hz	Simultaneous Measurement
Temperature Sensitivity (η_T)	25	µK/√Hz	Simultaneous Measurement
Isolation Factor	34	dB	Thermometry signal isolation from B-field
Diamond Crystal Type	1b HPHT	N/A	Natural ¹³C abundance
Diamond Dimensions	3 x 3 x 0.3	mm³	Used in experiment
NV^- Concentration	0.5	ppm	Estimated residual concentration
Remnant Nitrogen (N_g)	1.3	ppm	Residual P1 centers
Optical Collection Efficiency	56	%	Enhanced via S-LAH79 half-ball lens
External Magnetic Field (B₀)	1.6	mT	Aligned along [111] orientation
MW Reference Frequencies	5 and 7	kHz	For Frequency Modulation (FM)
MW Modulation Depth	0.55	MHz	Sinusoidal waveform
Volume-Normalized Sensitivity	542	nT · µm^3/2/√Hz	Effective sensing volume: 6 * 10⁷ µm³

Key Methodologies

The experiment relied on precise material engineering and advanced microwave/optical control to achieve high sensitivity and signal isolation.

Material Preparation: A general grade Type 1b HPHT diamond (3 x 3 x 0.3 mm³) with an initial Nitrogen concentration of approximately 30 ppm was used.
NV Creation: NV centers were generated via electron irradiation (1 MeV, 1 * 10¹⁹ e/cm²) followed by high-temperature annealing (950 °C for 4 hours in vacuum).
Optical Detection System: A 532 nm pump laser (600 mW total power) was focused onto the NV ensemble. Fluorescence was collected using a high-refractive index half-ball lens (S-LAH79, n ≈ 2.0) and an elliptic reflector to maximize photon collection (56%).
Balanced Detection: A home-made balanced circuit subtracted the reference photodiode output from the signal photodiode output to efficiently cancel common noise from the pump laser.
Dual Frequency Driving: Two independent microwave sources (MW1, MW2) were frequency-modulated using separate reference signals (5 kHz and 7 kHz, 0.55 MHz depth) to drive two specific NV transitions simultaneously, avoiding Coherent Population Trapping (CPT) effects.
Signal Multiplexing: Two lock-in amplifiers (LIA1, LIA2) independently detected the signals. The digitized outputs were then digitally summed (S_T) and subtracted (S_B) to isolate the thermal (ΔD) and magnetic (γΔB) components, respectively.
Isolation Optimization: The phase (ε) of the digital processing was tuned with 0.01° precision to minimize the intensity of the magnetic test signal on the temperature output (S_T), achieving the 34 dB isolation factor.

6CCVD Solutions & Capabilities

6CCVD specializes in providing high-purity, custom-engineered MPCVD diamond solutions that directly address the material limitations and performance requirements highlighted in this research.

Applicable Materials for Replication and Extension

The sensitivities achieved in this paper are limited by the quality of the HPHT diamond (e.g., remnant N, strain, and natural ¹³C abundance). To replicate or significantly extend this research, 6CCVD recommends:

6CCVD Material	Specification	Advantage over HPHT (Paper)
High-Purity Single Crystal Diamond (SCD)	SCD, N < 1 ppb, ¹²C enriched (< 0.1%)	Improved Coherence: Ultra-low nitrogen and ¹³C content drastically reduces decoherence (T₂*), leading to narrower ODMR linewidths (Δf) and higher contrast (C). This directly improves the shot-noise limited sensitivity (η_B, η_T).
High-Purity Polycrystalline Diamond (PCD)	Optical Grade PCD, up to 125mm diameter	Scalability: Enables large-area sensing arrays for wide-field magnetometry or thermometry, exceeding the 3x3 mm² scale used in the paper.
Custom NV Doping	Controlled N concentration (e.g., 0.1 ppm to 5 ppm)	Optimized Ensemble Density: Allows researchers to precisely tune the NV density (0.5 ppm used here) for maximum signal contrast and optimal sensing volume.

Customization Potential for Quantum Sensing

6CCVD’s in-house engineering capabilities are perfectly suited to meet the precise demands of advanced quantum sensing setups:

Custom Dimensions & Thickness: The paper used a 3 x 3 x 0.3 mm³ crystal. 6CCVD provides custom plates and wafers in SCD and PCD, with thicknesses ranging from 0.1 µm up to 500 µm, allowing optimization for specific optical collection geometries (e.g., thinner membranes for enhanced collection or thicker substrates for robust handling).
Ultra-Low Roughness Polishing: The use of a half-ball lens requires exceptional surface quality. 6CCVD guarantees Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD, ensuring minimal scattering losses and optimal coupling with high-refractive index optics (like the S-LAH79 lens used).
Integrated Metalization: While not explicitly used for NV sensing in this paper, 6CCVD offers custom metalization services (Au, Pt, Pd, Ti, W, Cu). This is crucial for integrating on-chip microwave antennas or micro-strip lines directly onto the diamond surface, simplifying the dual-frequency driving setup and improving MW delivery efficiency.

Engineering Support

The complexity of optimizing the isolation factor (34 dB achieved) and avoiding nonlinear effects like CPT requires deep material and quantum physics expertise.

Material Selection Consultation: 6CCVD’s in-house PhD team provides expert consultation on selecting the optimal diamond grade (SCD vs. PCD, N concentration, ¹³C enrichment) to maximize T₂* and contrast, thereby improving the theoretical shot-noise limit (η_B and η_T).
Design Optimization: We assist engineers in designing diamond geometries and surface preparations tailored for specific optical setups, such as optimizing thickness for high-NA objectives or integrating features for efficient MW delivery.
Global Logistics: 6CCVD ensures reliable, global shipping (DDU default, DDP available) of sensitive quantum materials, supporting international research collaborations.

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

View Original Abstract

Nitrogen-Vacancy (NV) spin in diamond is a versatile quantum sensor, being\nable to measure physical quantities such as magnetic field, electric field,\ntemperature, and pressure. In the present work, we demonstrate a multiplexed\nsensing of magnetic field and temperature. The dual frequency driving technique\nwe employ here is based on frequency-division multiplexing, which enables\nsensing both measurables in real time. The pair of NV resonance frequencies for\ndual frequency driving must be selected to avoid coherent population trapping\nof NV spin states. With an enhanced optical collection efficiency higher than\n50 $\%$ and a type 1b diamond crystal with natural abundance $^{13}$C spins, we\nachieve sensitivities of about 70 pT/$\sqrt{\mathrm{Hz}}$ and 25\n$\mu$K/$\sqrt{\mathrm{Hz}}$ simultaneously. A high isolation factor of 34 dB in\nNV thermometry signal against magnetic field was obtained, and we provide a\ntheoretical description for the isolation factor. This work paves the way for\nextending the application of NV quantum diamond sensors into more demanding\nconditions.\n

Tech Support

Original Source

DOI: https://doi.org/10.1103/physrevapplied.17.014009