High field magnetometry with hyperpolarized nuclear spins
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-09-19 |
| Journal | Nature Communications |
| Authors | ĂzgĂŒr Ćahin, Erica de Leon Sanchez, Sophie Conti, Amala Akkiraju, Paul Reshetikhin |
| Institutions | Lawrence Berkeley National Laboratory, Purdue University West Lafayette |
| Citations | 27 |
| Analysis | Full AI Review Included |
Technical Documentation: High-Field Magnetometry using Hyperpolarized ${}^{13}\text{C}$ in MPCVD Diamond
Section titled âTechnical Documentation: High-Field Magnetometry using Hyperpolarized ${}^{13}\text{C}$ in MPCVD DiamondâThis document analyzes the recent research demonstrating high-field magnetometry using hyperpolarized ${}^{13}\text{C}$ nuclear spins in diamond. This application leverages the long coherence times and high stability of diamond materials, aligning perfectly with 6CCVDâs expertise in custom MPCVD diamond solutions for quantum sensing and NMR applications.
Executive Summary
Section titled âExecutive SummaryâThe research successfully demonstrates a robust, high-field quantum magnetometer constructed from an ensemble of hyperpolarized ${}^{13}\text{C}$ nuclear spins within a single-crystal CVD diamond.
- High-Field Operation: Achieved stable magnetometry at $7 \text{ T}$, overcoming the technical challenges associated with electronic NV center control in the high-field regime.
- Exceptional Sensitivity: Demonstrated a single-shot sensitivity of $410 \text{ pT}/\sqrt{\text{Hz}}$ (via phase measurement), corresponding to an exquisite AC field precision of $\sim 10^{-11}$ over the $7 \text{ T}$ bias field.
- Extended Coherence: Utilized a spin-lock readout protocol to mitigate interspin dipolar coupling, extending the effective transverse sensor lifetime ($T_{2}^{\rho}$) to $> 30 \text{ s}$ (compared to the rapid free induction decay $T_{2}^{*} < 2 \text{ ms}$).
- High Resolution: Achieved a spectral resolution $< 100 \text{ mHz}$, with theoretical estimates suggesting a feasible resolution of $2.2 \text{ mHz}$ (a frequency precision of $3 \text{ ppt}$ at $7 \text{ T}$).
- Robust Methodology: The sensing protocol is robust against pulse errors and allows for continuous interrogation of the ${}^{13}\text{C}$ spins via RF techniques, enabling real-time tracking of changing magnetic fields.
- Future Potential: The work anticipates opportunities for microscale NMR chemical sensors constructed from hyperpolarized nanodiamonds and suggests significant gains through ${}^{13}\text{C}$ isotopic enrichment.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental results demonstrating the ${}^{13}\text{C}$ spin magnetometer performance at $7 \text{ T}$.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Operating Bias Field ($B_{0}$) | 7 | T | High-field regime |
| Single-Shot Sensitivity (Phase) | $410 \pm 90$ | pT/$\sqrt{\text{Hz}}$ | Measured at resonance frequency |
| Single-Shot Minimum Detectable Field | $\sim 70$ | pT | For $34 \text{ s}$ measurement time |
| Detection Bandwidth ($B$) | Up to 7 | kHz | Determined by interpulse interval $\tau$ |
| Spectral Resolution (Demonstrated) | $< 100$ | mHz | Extracted from oscillatory component $S_{0}$ |
| Spectral Resolution (Feasible Estimate) | 2.2 | mHz | Based on maximum achievable $T_{2}^{\rho}$ of $573 \text{ s}$ |
| Rotating Frame Lifetime ($T_{2}^{\rho}$) | $> 30$ | s | Achieved using spin-lock readout protocol |
| Longitudinal Lifetime ($T_{1}$) | $> 10$ | min | Characteristic of ${}^{13}\text{C}$ nuclei |
| Initial Polarization Level | $\sim 0.1$ | % | Achieved via optical hyperpolarization |
| NV Center Concentration | $\sim 1$ | ppm | Used for ${}^{13}\text{C}$ initialization |
| Resonance Linewidth ($\Delta f_{\text{res}}$) | $\sim 223$ | Hz | Measured from the decay component dip |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relies on high-quality single-crystal diamond and a specialized RF pulse sequence to achieve long coherence times in the coupled-sensor limit.
- Material Preparation: Single crystal CVD diamond (Element6) with $\sim 1 \text{ ppm}$ NV center concentration and natural abundance ${}^{13}\text{C}$ was used.
- Hyperpolarization (Initialization): ${}^{13}\text{C}$ nuclei were initialized at low magnetic field ($36-40 \text{ mT}$) via continuous laser illumination and chirped microwave excitation, leveraging the NV centers.
- High-Field Transfer: The hyperpolarized sample was transferred to the $7 \text{ T}$ bias field for magnetometry.
- Spin-Lock Protocol: A train of $\theta$ flip-angle RF pulses (e.g., $\theta \approx 75^{\circ}$) was applied to the ${}^{13}\text{C}$ spins, separated by short interpulse periods ($\tau < 100 \text{ ”s}$). This sequence suppresses dipolar interactions, extending $T_{2}^{\rho}$.
- AC Field Application: A time-varying AC magnetic field ($B_{\text{AC}}$) was applied parallel to the ${}^{13}\text{C}$ quantization axis ($z$-coil).
- Inductive Readout: The ${}^{13}\text{C}$ Larmor precession signal was continuously measured inductively in the acquisition windows ($\tau_{\text{acq}}$) between pulses using a fast arbitrary waveform transceiver.
- Signal Extraction: The oscillatory component ($S_{0}$) of the signal was analyzed via Fourier transform to extract the frequency and amplitude of the applied $B_{\text{AC}}$, demonstrating high spectral resolution.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials and customization services required to replicate, optimize, and extend this high-field quantum sensing research. Our capabilities directly address the material requirements for enhancing sensitivity and integrating the sensor into complex RF/optical setups.
Applicable Materials
Section titled âApplicable Materialsâ| Research Requirement | 6CCVD Material Solution | Optimization Potential |
|---|---|---|
| Base Material (SCD) | Optical Grade Single Crystal Diamond (SCD): High-purity SCD wafers are essential for low-defect NV creation and achieving the long $T_{1}$ and $T_{2}^{\rho}$ lifetimes observed. | We offer SCD substrates up to $500 \text{ ”m}$ thickness, ensuring ample volume for bulk sensing experiments. |
| Sensitivity Enhancement | Custom Isotope-Controlled SCD/PCD: The paper suggests a $10\text{x}$ sensitivity gain using $10%$ ${}^{13}\text{C}$ enriched samples. | 6CCVD specializes in custom-grown SCD and PCD with precise isotopic control to maximize the density of sensor spins. |
| Nanodiamond (ND) Applications | High-Purity Polycrystalline Diamond (PCD): For future microscale NMR detectors using NDs, high-quality PCD wafers are the ideal starting material for milling and processing. | We provide PCD wafers up to $125 \text{ mm}$ in diameter and up to $500 \text{ ”m}$ thick, suitable for large-scale ND production. |
| BDD for Electrochemistry | Boron-Doped Diamond (BDD): While not used here, BDD is critical for related electrochemistry and sensing applications. | We supply BDD films with tunable doping levels for integrated sensor platforms. |
Customization Potential
Section titled âCustomization PotentialâTo move this research from proof-of-concept to integrated device engineering, 6CCVD offers critical fabrication and processing capabilities:
- Precision Polishing: The optical initialization of NV centers requires minimal scattering. We guarantee ultra-smooth surfaces on SCD with $R_{\text{a}} < 1 \text{ nm}$, and on inch-size PCD with $R_{\text{a}} < 5 \text{ nm}$.
- Custom Dimensions and Thickness: We provide SCD and PCD plates/wafers in custom dimensions, allowing researchers to optimize sample geometry for specific RF coil designs and high-field magnet bore constraints. Substrates up to $10 \text{ mm}$ thick are available.
- Integrated Metalization: The inductive readout requires precise RF coil integration. 6CCVD offers in-house metalization services, including Au, Pt, Pd, Ti, W, and Cu, enabling the direct deposition and patterning of contacts and micro-coils onto the diamond surface.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team provides expert consultation to assist researchers in material selection and optimization for similar High-Field Quantum Sensing and Microscale NMR projects. We can advise on:
- Optimizing ${}^{13}\text{C}$ concentration for maximum signal while managing dipolar coupling effects.
- Selecting appropriate SCD/PCD grades for specific NV creation and annealing protocols (e.g., high-temperature rapid thermal annealing referenced in the paper).
- Designing custom metalization stacks for high-frequency RF control and readout at $7 \text{ T}$ and beyond.
Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Quantum sensors have attracted broad interest in the quest towards sub-micronscale NMR spectroscopy. Such sensors predominantly operate at low magnetic fields. Instead, however, for high resolution spectroscopy, the high-field regime is naturally advantageous because it allows high absolute chemical shift discrimination. Here we demonstrate a high-field spin magnetometer constructed from an ensemble of hyperpolarized 13 C nuclear spins in diamond. They are initialized by Nitrogen Vacancy (NV) centers and protected along a transverse Bloch sphere axis for minute-long periods. When exposed to a time-varying (AC) magnetic field, they undergo secondary precessions that carry an imprint of its frequency and amplitude. For quantum sensing at 7T, we demonstrate detection bandwidth up to 7 kHz, a spectral resolution < 100mHz, and single-shot sensitivity of 410pT $$/\sqrt{{{{{{{{\rm{Hz}}}}}}}}}$$ <mml:math xmlns:mml=âhttp://www.w3.org/1998/Math/MathMLâ> <mml:mo>/</mml:mo> <mml:msqrt> <mml:mrow> <mml:mi>Hz</mml:mi> </mml:mrow> </mml:msqrt> </mml:math> . This work anticipates opportunities for microscale NMR chemical sensors constructed from hyperpolarized nanodiamonds and suggests applications of dynamic nuclear polarization (DNP) in quantum sensing.