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 | ĂzgĂźr Ĺahin, Erica de Leon Sanchez, Sophie Conti, Amala Akkiraju, Paul Reshetikhin |
| Institutions | University of California, Berkeley, Purdue University West Lafayette |
| Citations | 27 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a novel approach to high-field quantum sensing by leveraging hyperpolarized 13C nuclear spins in diamond, offering a pathway to microscale Nuclear Magnetic Resonance (NMR) spectroscopy for engineering applications.
- High-Field Operation: The sensor operates robustly at a high bias magnetic field (B0 = 7 T), a regime where traditional electron-spin (NV center) quantum sensors face significant technical challenges due to rapid electronic gyromagnetic ratio scaling.
- Enhanced Coherence: A pulsed spin-lock sequence (analogous to Floquet prethermalization) is employed to suppress inter-spin dipolar coupling, extending the effective transverse coherence time (T2â) of the 13C spins to > 30 seconds.
- High Sensitivity and Resolution: The sensor achieves a single-shot sensitivity of 410 pT/sqrt(Hz) (via phase tracking) and a demonstrated spectral resolution better than 100 mHz.
- Continuous Tracking: The 13C spins are continuously interrogated non-destructively via RF techniques, allowing real-time tracking of time-varying (AC) magnetic fields over extended periods (up to 275k pulses demonstrated).
- Microscale Potential: The technology anticipates the development of microscale NMR chemical sensors using hyperpolarized nanodiamonds, enabling sub-micron spatial resolution for chemical analysis.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Bias Magnetic Field (B0) | 7 | T | Operating regime for magnetometry |
| Single-Shot Sensitivity (Phase) | 410 Âą 90 | pT/sqrt(Hz) | Measured via signal phase tracking |
| Single-Shot Sensitivity (Amplitude) | 760 Âą 127 | pT/sqrt(Hz) | Measured via signal amplitude tracking |
| AC Field Precision | ~10-11 | N/A | Relative precision over the 7 T bias field |
| Demonstrated Detection Bandwidth (B) | Up to 7 | kHz | Limited by current Rabi frequency (~20 kHz) |
| Estimated Feasible Bandwidth (B) | ~500 | kHz | Requires improved filling factor and RF coil Q-factor |
| Demonstrated Spectral Resolution (δf) | < 100 | mHz | Limited by current data acquisition memory (35 s) |
| Estimated Feasible Spectral Resolution (δf) | 2.2 | mHz | Based on full T2â decay time (> 573 s) |
| Transverse Lifetime (T2â) | > 30 | s | Rotating frame, achieved under spin-lock |
| Longitudinal Lifetime (T1) | > 10 | min | |
| Sensor Material | Single-crystal diamond | N/A | ~1 ppm NV concentration, natural 13C abundance |
| Current Hyperpolarization Level | ~0.1 | % | Enhanced polarization via NV centers |
| Total Pulses Applied | > 275k | N/A | Continuous interrogation period |
Key Methodologies
Section titled âKey MethodologiesâThe experiment uses a hybrid quantum sensor approach where NV centers initialize the 13C spins, which then act as the primary magnetic field sensors under a pulsed RF protocol.
- Sample and Initialization: A single-crystal diamond with NV centers and natural 13C abundance was used. 13C nuclear spins were hyperpolarized (polarization > 10,000-fold thermal) via continuous laser illumination and chirped microwave excitation at a low magnetic field (36-40 mT).
- High-Field Transfer: The hyperpolarized sample was transferred to the high-field setup operating at B0 = 7 T. The AC magnetic field (BAC) was applied along the 13C quantization axis (z-axis) using a z-coil.
- Spin-Lock Sequence: A train of RF pulses (θ flip-angle, high duty cycle 19-54%) was applied to the 13C spins. This sequence drives the spins into the transverse (x) axis of the rotating frame, where they are protected from rapid dipolar decay (T2â > 30 s).
- Inductive Readout: During the acquisition windows (tacq) between the RF pulses, the 13C Larmor precession signal (at 20 MHz) was inductively measured and digitized using a fast arbitrary waveform transceiver.
- Signal Processing: The raw signal was Fourier transformed to extract the magnitude and phase of the heterodyned Larmor precession, which represents the transverse magnetization component (S).
- AC Field Detection: When BAC is applied, the spins undergo a secondary precession. The oscillatory component (So) of the signal is analyzed via Fourier Transform to identify the primary (fAC) and secondary (2fAC) harmonic peaks, yielding the frequency and amplitude of the external AC field.
- Resonance Condition: Optimal sensing occurs near the resonance condition, fres = θ / (2ĎĎ), where the AC field periodicity matches the time required for a 2Ď rotation in the rotating frame.
Commercial Applications
Section titled âCommercial ApplicationsâThe ability to perform high-resolution, high-field magnetometry using robust, long-lived nuclear spins opens several avenues for commercial and research applications:
- Microscale NMR Spectroscopy: Developing microscale NMR detectors using hyperpolarized nanodiamond particles. This enables chemical shift discrimination of analyte nuclei (e.g., 1H) with sub-micron spatial resolution, crucial for biological and material science analysis.
- Condensed Matter Physics: Non-invasive, high spatial resolution visualization of magnetic phenomena at high fields, including:
- Mapping domain walls in 2D ferromagnets.
- Studying antiferromagnetic and spin-glass phases.
- Investigating reentrant Hofstadter phases in twisted bilayer graphene.
- Robust Sensing in Scattering Media: Utilizing RF-interrogated nuclear spins provides immunity to optical scattering, enabling magnetometry and NMR sensing in challenging environments like underwater or biological tissues, where optical NV sensors fail.
- High-Field Quantum Gyroscopes: The stable, long-lived nuclear spin states are ideal for constructing robust, high-field nuclear spin gyroscopes.
- Multiplexed Field Mapping: The single-shot Fourier reconstruction capability allows simultaneous discernment of multiple AC fields, facilitating complex, high-precision field mapping in industrial or research settings.
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.