Multiplexed Sensing of Magnetic Field and Temperature in Real Time Using a Nitrogen-Vacancy Ensemble in Diamond
At a Glance
Section titled âAt a Glanceâ| 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 | University of Maryland, College Park, Hanyang University |
| Citations | 43 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a highly sensitive, real-time multiplexed quantum sensor utilizing Nitrogen-Vacancy (NV) spin ensembles in diamond, capable of simultaneously measuring magnetic field and temperature.
- Core Achievement: Implementation of Frequency-Division Multiplexing (FDM) via dual frequency microwave driving, enabling concurrent, real-time measurement of magnetic field (B) and temperature (T).
- High Sensitivity: Achieved simultaneous sensitivities of 70 pT/sqrt(Hz) for magnetic field and 25 ”K/sqrt(Hz) for temperature.
- High Isolation: Demonstrated an isolation factor of 34 dB in the NV thermometry signal against magnetic field fluctuations, crucial for reliable thermal sensing in noisy environments.
- Mitigation of Coherent Trapping: Specific NV hyperfine transitions were selected to avoid Coherent Population Trapping (CPT), which otherwise diminishes the Optically Detected Magnetic Resonance (ODMR) contrast.
- Enhanced Optics: Improved optical collection efficiency (approx. 56%) was achieved using a high-refractive index half-ball lens (S-LAH79, n ~ 2.0) and an elliptic reflector.
- Material Basis: Used a Type 1b HPHT diamond crystal with natural 13C abundance and an NV- density of 0.5 ppm.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Magnetic Field Sensitivity (Experimental) | 70 | pT/sqrt(Hz) | Simultaneous, real-time sensing |
| Temperature Sensitivity (Experimental) | 25 | ”K/sqrt(Hz) | Simultaneous, real-time sensing |
| Isolation Factor (T vs. B) | 34 | dB | Isolation of thermometry signal from magnetic field |
| Zero-Field Splitting Constant (k) | 74.2 | kHz/K | Temperature dependence of D |
| NV Diamond Type | 1b | HPHT | High-Pressure High-Temperature grown |
| Diamond Dimensions | 3 x 3 x 0.3 | mm3 | Sample size |
| NV- Concentration | 0.5 | ppm | Achieved via irradiation/annealing |
| Remnant Nitrogen (Ng) | 1.3 | ppm | Residual P1 center concentration |
| Optical Collection Efficiency | ~56 | % | Total photon collection efficiency |
| Pump Laser Wavelength | 532 | nm | Green pump laser (Millennia eV) |
| Pump Laser Power (Excitation) | 400 | mW | Power exciting the NV ensemble |
| Photo-induced Current (iph) | 11 | mA | Typical current from photodiode |
| Half-Ball Lens Material | S-LAH79 | n ~ 2.0 | High refractive index material |
| External Static Magnetic Field (B0) | 1.6 | mT | Produced by permanent magnet |
| MW Reference Frequencies (fr1, fr2) | 5, 7 | kHz | Used for frequency modulation |
| MW Modulation Depth | 0.55 | MHz | Depth of frequency modulation |
| MW Output Power (PMW) | 30 | mW | Typical power driving the antenna |
| Effective Sensing Volume | ~6 x 107 | ”m3 | Volume of NV ensemble interrogated |
| Volume-Normalized Sensitivity | 542 | nT · ”m3/2/sqrt(Hz) | Metric for sensor performance scaling |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relies on precise material engineering and a sophisticated dual-frequency detection scheme based on Frequency-Division Multiplexing (FDM).
-
NV Center Creation:
- Start with Type 1b HPHT diamond (initial Ng ~30 ppm).
- Irradiation: Electron irradiation at 1 MeV with a dose of 1 x 1019 e/cm2.
- Annealing: Vacuum annealing at 950 °C for 4 hours to mobilize vacancies and form NV- centers (resulting NV- concentration: 0.5 ppm).
-
Optical Detection System:
- A 532 nm green pump laser (600 mW total output) is used for excitation and split for balanced detection.
- Fluorescence is collected using a high-refractive index half-ball lens (S-LAH79) glued to the diamond, coupled with an elliptic reflector to maximize the photon escape cone and collection efficiency (~56%).
- A balanced photodiode circuit cancels common-mode noise from the pump laser.
-
Dual Frequency Microwave Driving (FDM):
- Two independent microwave sources (MW1, MW2) are used to drive two distinct NV spin transitions (f- and f+) simultaneously.
- The transition pair is selected (blue/yellow arrows in Fig. 2a) to avoid V-type level configuration and subsequent Coherent Population Trapping (CPT), ensuring maximum ODMR contrast.
- MW1 and MW2 are frequency-modulated (FM) by reference signals (5 kHz and 7 kHz, respectively).
-
Signal Processing and Multiplexing:
- Two independent Lock-In Amplifiers (LIA1, LIA2) detect the signals S1(t) and S2(t) corresponding to the two reference frequencies.
- The outputs are digitally processed (summed and subtracted) in software:
- Subtracted Signal (SB): Proportional to 2αÎB(t), isolating the magnetic field variation.
- Summed Signal (ST): Proportional to 2αÎD(t), isolating the thermal variation.
- A digital phase tuning (Δ) is applied to the summation/subtraction process to minimize magnetic field leakage into the temperature signal, optimizing the isolation factor (34 dB).
Commercial Applications
Section titled âCommercial ApplicationsâThe ability to perform high-sensitivity, real-time, isolated multiplexed sensing of magnetic fields and temperature extends the utility of quantum diamond sensors into demanding industrial and scientific environments.
- Operando Monitoring (Batteries/Chemicals):
- Monitoring chemical reactions (e.g., in commercial Na/Li-ion cells) where both magnetic field changes (charge currents) and thermal events (heat production) occur simultaneously.
- Real-time monitoring of biological processes (e.g., embryogenesis, in-vitro monitoring) where heat and charge currents are generated.
- Biomagnetism and Medical Diagnostics:
- Detection of biological signals (e.g., single-neuron action potentials, mammalian muscle activity) where thermal drift must be precisely isolated from weak magnetic signals.
- High-Precision Metrology:
- Use as a highly sensitive thermometer (25 ”K/sqrt(Hz)) in environments where magnetic field noise is prevalent (e.g., cryogenic systems, quantum computing hardware).
- Magnetic Material Characterization:
- Analyzing magnetic nanoparticles or materials whose Curie temperature is near room temperature, where magnetic response is highly temperature-dependent.
- Quantum Sensing Components:
- Providing robust, high-dynamic-range vector magnetometry and thermometry components for integrated quantum diamond microscopes and sensors.
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