Atomic-Scale Nuclear Spin Imaging Using Quantum-Assisted Sensors in Diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-01-07 |
| Journal | Physical Review X |
| Authors | A. Ajoy, U. Bissbort, M.âD. Lukin, R.âL. Walsworth, P Cappellaro |
| Institutions | Singapore University of Technology and Design, Center for Astrophysics Harvard & Smithsonian |
| Citations | 70 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Atomic-Scale Nuclear Spin Imaging
Section titled âTechnical Documentation & Analysis: Atomic-Scale Nuclear Spin ImagingâExecutive Summary
Section titled âExecutive SummaryâThis research demonstrates a breakthrough in quantum sensing, achieving atomic-scale spatial resolution for nuclear spin imaging in complex biomolecules using Nitrogen Vacancy (NV) centers in diamond.
- Core Achievement: Atomic-scale (sub-Angstrom) reconstruction of nuclear spin positions in biomolecules (e.g., CXCR4 receptor) in their native environment, overcoming limitations of X-ray crystallography and conventional NMR.
- Methodology: Utilizes a quantum-enhanced sensing protocol based on Filtered Cross-Polarization (FCP) combined with a magnetic field gradient, creating a sharp dynamic frequency filter (Bragg grating).
- Material Requirement: Requires high-purity, isotopically engineered Single Crystal Diamond (SCD) with ultra-shallow NV centers (1-3 nm depth) to maximize coupling to surface-bound molecules.
- Resolution Enhancement: The use of the intrinsic $^{15}$N nuclear spin as a quantum memory extends the coherence time ($T_{2n}$ up to 10 ms), enabling a tenfold improvement in spatial resolution compared to standard dynamical decoupling (DD) methods.
- Technical Output: Generates multi-dimensional NMR spectra (1D and 2D) that encode spatial correlations and lift spectral degeneracies, crucial for structure reconstruction.
- 6CCVD Value Proposition: 6CCVD provides the essential high-purity, low-strain SCD substrates (Ra < 1nm polished) necessary for precise shallow NV creation and subsequent robust surface functionalization required for this advanced bio-imaging application.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the analysis and simulations of the quantum-assisted sensing protocol:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Center Depth | 1 - 3 | nm | Required distance from the diamond surface for optimal coupling. |
| Target Spin Distance | 2 - 5 | nm | Distance of biomolecule nuclear spins from the NV center. |
| Ancillary $^{15}$N Coherence Time ($T_{2n}$) | 8 - 10 | ms | Limits the maximum gradient evolution time ($T_g$). |
| Enhanced Frequency Resolution ($\delta A$) | $\sim 100$ | Hz | Achieved via the dynamic frequency filter (Bragg grating). |
| Sensing Bandwidth ($\Delta A$) | 10 - 50 | times larger | Compared to standard DD-based sensing protocols. |
| Total Gradient Time ($T_g$) | $\approx 6$ | ms | Used in $F=30$ steps for high spatial resolution. |
| Simulated Polarization Time ($t$) | 720 | ”s | Total time for 1D spectrum acquisition. |
| Volume Uncertainty (Spatial Resolution) | 1.2 to 10 | Ă 3 | Achieved spatial resolution for spin position reconstruction. |
| $^{13}$C Larmor Frequency ($\omega_L$) | 2 | MHz | Used in simulations for the CXCR4 binding site. |
| Minimum Dipolar Coupling ($B_{\perp}$) | 250 | Hz | Minimum coupling of interest for $^{13}$C spins. |
| Rotating Frame Coherence Time ($T_{1\rho}$) | $\approx 2$ | ms | Limits the total measurement time for SNR. |
Key Methodologies
Section titled âKey MethodologiesâThe atomic-scale nuclear spin imaging protocol relies on precise quantum control sequences applied to ultra-pure diamond substrates:
- Qubit Initialization and Polarization: The NV electronic spin is optically polarized and initialized. The ancillary $^{15}$N nuclear spin (quantum memory) is also initialized.
- Filtered Cross-Polarization (FCP): Polarization is transferred from the NV electronic spin to the target nuclear spins in the biomolecule over time $t/F$ using a spin-lock Hamiltonian.
- Quantum Memory Mapping (SWAP): The NV electronic spin state is mapped onto the long-lived $^{15}$N nuclear spin memory via a SWAP gate.
- Gradient Evolution: While the NV state is stored in the $^{15}$N memory, the external nuclear spins evolve under a strong magnetic field gradient (often provided intrinsically by the NV center itself). This evolution time ($t_g$) creates a sharp dynamic frequency filter.
- Homonuclear Decoupling: Decoupling sequences (e.g., WAHUHA) are embedded during the spin-lock and gradient evolution periods to cancel low-frequency dephasing noise and narrow the intrinsic NMR linewidth of the dense sample.
- Signal Acquisition (Reverse Sense): The sequence is repeated $F$ times to build the sharp filter. Polarization is transferred back to the NV center and measured optically via spin-dependent photoluminescence (PL) contrast.
- 2D NMR Spectroscopy: By allowing the polarized nuclear spins to diffuse freely for a time $t_d$ before the reverse sense step, 2D correlated spectra are acquired, revealing spin-spin couplings and constraining relative positions.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâReplicating and advancing this cutting-edge quantum sensing research requires diamond materials engineered to the highest standards of purity, surface quality, and dimensional control. 6CCVD is uniquely positioned to supply the necessary components.
Applicable Materials for Quantum Sensing
Section titled âApplicable Materials for Quantum Sensingâ| Research Requirement | 6CCVD Solution | Technical Justification |
|---|---|---|
| High Coherence Time ($T_2$) | Isotopically Purified SCD | Low concentration of $^{13}$C (natural abundance 1.1%) is critical to minimize magnetic noise and maximize NV electronic and nuclear spin coherence times ($T_2$ and $T_{2n}$ up to 10 ms). |
| Ultra-Shallow NV Centers | High-Purity SCD Substrates | SCD plates provide the necessary low-defect, low-strain crystalline foundation for subsequent precise shallow NV creation via ion implantation or delta doping (1-3 nm depth). |
| Surface Functionalization | SCD with Ra < 1 nm Polishing | Ultra-smooth surfaces are mandatory for reliable chemical functionalization (e.g., EDC/NHS reaction) and stable anchoring of biomolecules (CXCR4 receptor) close to the NV sensor. |
| Integrated Qubit Memory | SCD Substrates (for $^{15}$N implantation) | While the paper uses intrinsic $^{15}$N, 6CCVD supplies the base SCD material suitable for controlled $^{15}$N implantation to create the ancillary quantum memory qubit. |
Customization Potential & Engineering Support
Section titled âCustomization Potential & Engineering Supportâ6CCVDâs advanced manufacturing capabilities directly address the needs of quantum sensing research:
- Custom Dimensions and Thickness:
- The research requires high-quality SCD wafers. 6CCVD provides SCD plates up to 500 ”m thick and can supply substrates up to 10 mm for robust experimental setups.
- We offer custom laser cutting to produce unique geometries or small chips required for integration into microwave/RF antennae or microfluidic systems.
- Advanced Metalization Services:
- The experimental setup often requires integrated microwave/RF antennae or magnetic tips (mentioned in references [18, 35]).
- 6CCVD offers in-house metalization using materials such as Au, Pt, Pd, Ti, W, and Cu for creating high-performance transmission lines or magnetic field gradient sources directly on the diamond surface.
- Surface Preparation and Polishing:
- Achieving atomic-scale imaging requires pristine surfaces. 6CCVD guarantees SCD polishing with roughness Ra < 1 nm, ensuring optimal conditions for biomolecule attachment and minimizing surface noise.
- Engineering Support:
- 6CCVDâs in-house PhD team specializes in material science for quantum applications. We can assist researchers in selecting the optimal isotopic purity, crystal orientation, and surface termination required for Atomic-Scale NMR and Bio-Imaging projects. We offer consultation on material specifications to maximize $T_2$ and minimize surface defects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Nuclear spin imaging at the atomic level is essential for the understanding of fundamental biological phenomena and for applications such as drug discovery. The advent of novel nanoscale sensors promises to achieve the long-standing goal of single-protein, high spatial-resolution structure determination under ambient conditions. In particular, quantum sensors based on the spin-dependent photoluminescence of nitrogen-vacancy (NV) centers in diamond have recently been used to detect nanoscale ensembles of external nuclear spins. While NV sensitivity is approaching single-spin levels, extracting relevant information from a very complex structure is a further challenge since it requires not only the ability to sense the magnetic field of an isolated nuclear spin but also to achieve atomic-scale spatial resolution. Here, we propose a method that, by exploiting the coupling of the NV center to an intrinsic quantum memory associated with the nitrogen nuclear spin, can reach a tenfold improvement in spatial resolution, down to atomic scales. The spatial resolution enhancement is achieved through coherent control of the sensor spin, which creates a dynamic frequency filter selecting only a few nuclear spins at a time. We propose and analyze a protocol that would allow not only sensing individual spins in a complex biomolecule, but also unraveling couplings among them, thus elucidating local characteristics of the molecule structure.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 1986 - NMR of Proteins and Nucleic Acids