Three-dimensional magnetic resonance tomography with sub-10 nanometer resolution
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-01-25 |
| Journal | npj Quantum Information |
| Authors | Mohammad T. Amawi, Andrii Trelin, You Huang, Paul Weinbrenner, Francesco Poggiali |
| Institutions | University of Rostock, Technical University of Munich |
| Citations | 4 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a breakthrough in nanoscale magnetic resonance tomography (MRT), achieving sub-10 nanometer resolution in three dimensions using Nitrogen-Vacancy (NV) centers in diamond.
- Record Resolution: Achieved a spatial resolution down to 5.9 ± 0.1 nm, which is comparable to or better than the best existing super-resolution optical microscopy techniques (e.g., PALM/STORM).
- 3D Fourier Acceleration: Implemented Fourier-accelerated 3D imaging by using lithographically fabricated U-shaped microwires to generate three linearly independent, switchable magnetic field gradients.
- Gradient Device: The device utilizes a 200 nm Gold film microstructure on a densely doped CVD diamond substrate ([NV] â 0.13 ppb) to produce gradients of approximately 2 G”m-1.
- High-Speed Control: Gradient pulses are controlled by fast switches (1 ns rise/fall time) and corrected via hardware integration of the current integral to mitigate shot-to-shot fluctuations and maintain coherence (T2,â„ â 8.64 ”s).
- Compressed Sensing Zoom: Demonstrated a novel compressed sensing scheme (âFourier zoomingâ) based on equidistant k-space undersampling and aliasing, allowing for efficient acquisition of spatially localized volumes of interest (e.g., clusters of NV centers) with reduced data points (up to 18x reduction).
- Impact: This technique establishes a three-dimensional super-resolution method for optically readable spin qubits, enabling 3D structure analysis and approaching the positioning accuracy required for site-directed spin labeling.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Spatial Resolution (Best Axis) | 5.9 ± 0.1 | nm | Uncertainty in 3D MRT imaging (ÎX) |
| Spatial Resolution (Full 3D) | (5.9, 9.9, 14.7) | nm | Resolution across the three gradient axes |
| Gradient Field Magnitude | â 2 | G”m-1 | Generated by U-microstructure wires |
| Gradient Field Magnitude (SI) | 2 * 102 | Tm-1 | SI equivalent of the gradient field |
| NV Center Density | â 0.13 | ppb | Element Six General Grade CVD diamond doping |
| Wire Material Stack | 200 nm Au on 10 nm Cr | nm | Microfabricated U-structure composition |
| Wire Dimensions (Arms) | 5 ”m long, 500 nm wide | ”m, nm | U-microstructure geometry |
| Bias Magnetic Field (B0) | â 76 | G | Applied homogeneous field |
| Gradient Pulse Rise/Fall Time | 1 | ns | Performance of fast switches (ic-Haus HGP) |
| Coherence Time (T2,â„) | 8.64 ± 0.10 | ”s | Measured decay time under gradient current I2 |
| Imaging Depth | â 6 | ”m | Distance below the diamond surface |
| Acquisition Speed-up (Zoom) | Up to 18 | Factor | Achieved using aliasing-based compressed sensing |
Key Methodologies
Section titled âKey Methodologiesâ- Device Fabrication: A U-shaped microstructure consisting of a 200 nm Gold film atop a 10 nm Chromium layer was fabricated via lift-off photolithography directly onto a densely doped CVD diamond substrate hosting NV centers.
- Gradient Generation: Three independent currents (I1, I2, I3) were driven through the three arms of the U-structure, generating three linearly independent magnetic field gradients (â 2 G”m-1) in the imaging plane â 6 ”m beneath the diamond surface.
- Pulse Control and Stability: Gradient currents were generated by switching a stable voltage source using ultra-fast switches (ic-Haus HGP) to ensure nearly rectangular pulses with 1 ns rise/fall times, crucial for satisfying the linear phase-encoding approximation.
- Decoherence Mitigation: To correct for current fluctuations and residual nonlinearities, the current integral â«I(t)dt was acquired via hardware integration for every pulse. This value was used to define a corrected time axis (teff), suppressing chirps and improving the effective coherence time (T2,â„).
- 3D Spectroscopy: A Hahn Echo sequence was employed, incorporating the three gradient pulses consecutively. The accumulated phase shift translates into an oscillatory spin signal (Sz(t)), which is a linear superposition of signals from all NV centers.
- Standard Image Reconstruction: The set of three Larmor frequency shifts (ÏI1, ÏI2, ÏI3) corresponding to the NV center positions was recovered by performing a 3D inverse Fourier transform of the time-domain data (k-space).
- Compressed Sensing (Fourier Zooming): For efficient imaging of localized clusters, the time-domain signal was equidistantly undersampled. This induced aliasing, shifting the signal frequency band to a contiguous low-frequency window, effectively implementing a zoom and reducing the required data points by over an order of magnitude without requiring L1 minimization.
Commercial Applications
Section titled âCommercial Applicationsâ- Structural Biology and Protein Analysis:
- Direct, real-space 3D imaging of spin-labeled proteins, providing distance constraints >80 A, which is currently a blind spot for standard Electron Spin Resonance (ESR) spectroscopy.
- Enabling Single-Molecule MRI (SM-MRI) by using a single NV center as a detector for electron spin labels on external molecules.
- Quantum Information and Computing:
- Selective addressing and manipulation of individual, coherently coupled qubits within densely doped NV center ensembles, facilitating the development of robust quantum registers.
- High-resolution mapping of crystal strain, enabling applications in directional detection of dark matter or other elementary particles.
- Nanoscale Metrology and Sensing:
- Super-resolved tracking and measurement of forces (e.g., magnetic or mechanical) at the nanoscale, particularly when applied to NV centers embedded in nanodiamonds.
- Potential for label-free chemical contrast imaging within opaque samples, providing an ultimate microscope capability for nuclear spins.
View Original Abstract
Abstract We demonstrate three-dimensional magnetic resonance tomography with a resolution down to 5.9 ± 0.1 nm. Our measurements use lithographically fabricated microwires as a source of three-dimensional magnetic field gradients, which we use to image NV centers in a densely doped diamond by Fourier-accelerated magnetic resonance tomography. We also demonstrate a compressed sensing scheme, which allows for direct visual interpretation without numerical optimization and implements an effective zoom into a spatially localized volume of interest, such as a localized cluster of NV centers. It is based on aliasing induced by equidistant undersampling of k-space. The resolution achieved in our work is comparable to the best existing schemes of super-resolution microscopy and approaches the positioning accuracy of site-directed spin labeling, paving the way to three-dimensional structure analysis by magnetic-gradient based tomography.