Low-Field Nuclear Polarization Using Nitrogen Vacancy Centers in Diamonds
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2018-02-08 |
| Journal | Physical Review Letters |
| Authors | Yonatan Hovav, Boris Naydenov, Fedor Jelezko, Nir BarâGill |
| Institutions | Canadian Institute for Advanced Research, Center for Integrated Quantum Science and Technology |
| Citations | 15 |
| Analysis | Full AI Review Included |
Technical Analysis and Documentation for 6CCVD
Section titled âTechnical Analysis and Documentation for 6CCVDâExecutive Summary
Section titled âExecutive SummaryâThis research introduces the refocused-NOVEL (rNOVEL) sequence, a robust technique utilizing Nitrogen-Vacancy (NV) centers in diamond for efficient Dynamic Nuclear Polarization (DNP) transfer, particularly effective in environments characterized by low magnetic fields and high noise.
- Low-Field Operation: rNOVEL enables robust nuclear polarization transfer (e.g., to 13C nuclei) at low magnetic fields (< 500 Gauss), overcoming the precise alignment requirements of high-field methods.
- Enhanced Polarization: Numerical simulations demonstrate that rNOVEL achieves up to ~13% nuclear polarization under realistic dephasing noise, representing a factor of two improvement compared to the traditional NOVEL sequence (~6%).
- Improved Noise Decoupling: The refocused sequence structure, analogous to CPMG, significantly decouples the NV electronic spin from environmental noise, maintaining higher polarization fidelity in imperfect systems, such as those employing shallow NVs.
- Applicability: This technique is critical for applications where precise magnetic alignment is impractical or undesired, including portable quantum sensors, nuclear magnetic resonance (NMR) spectroscopy, and high-resolution imaging using nanodiamonds.
- Material Requirement: Replicating and extending this research requires high-purity, low-strain, Single Crystal Diamond (SCD) material with carefully controlled NV defect creation and excellent surface finish, capabilities inherent to 6CCVDâs MPCVD process.
Technical Specifications
Section titled âTechnical SpecificationsâThe following parameters summarize the operating conditions and key results for the refocused-NOVEL (rNOVEL) sequence simulations, specifically targeting 13C polarization via NV centers.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| External Magnetic Field ($B_0$) | 80 | Gauss | Low-field regime tested; generally < 500 Gauss |
| Initialization Wavelength | 532 | nm | Green laser required for NV spin polarization |
| Target Nucleus | Carbon-13 (13C) | N/A | Nearest neighboring nucleus coupling |
| NV Spin State Subspace | $S=1 \to \left | 0\right\rangle, \left | -1\right\rangle$ |
| NV-Nucleus Parallel Hyperfine ($A_{\parallel}$) | 30 | kHz | Used for calculation (model system) |
| NV-Nucleus Perpendicular Hyperfine ($A_{\perp}$) | 40 | kHz | Used for calculation (model system) |
| Maximum Nuclear Polarization (rNOVEL, w/ noise) | ~13 | % | Achieved with $N=16$ to 32 repetitions |
| Maximum Nuclear Polarization (NOVEL, w/ noise) | ~6 | % | Achieved at low $\Omega_{SL}$ |
| Sequence Periodicity ($\tau$) | 2 | ”s | Total sequence time $T = N\tau$ |
| Larmor Frequency ($\omega_n / 2\pi$) | ~0.1 | MHz | Nuclear precession frequency |
| Fast Noise Correlation Time ($\tau_{c}$) | 11 | ”s | Parameter for Ornstein-Uhlenbeck noise model |
| Slow Noise Correlation Time ($\tau_{c}$) | 150 | ”s | Parameter for Ornstein-Uhlenbeck noise model |
Key Methodologies
Section titled âKey MethodologiesâThe experimental approach leverages the unique coherence properties of the NV center in diamond, utilizing high-frequency microwave (MW) pulse sequences in conjunction with optical initialization and readout.
- Optical Initialization: An initial laser pulse (532 nm green light) polarizes the NV electronic spin ($S=1$) to its $|0\rangle$ ground state, establishing the non-equilibrium polarization source.
- MW Preparation: A preparatory MW pulse sets up the necessary spin superposition for the sequence initiation.
- Refocused-NOVEL (rNOVEL) Sequence: Polarization transfer is achieved through $N$ repetitions of a $\tau/2$ sequence structure:
- The sequence consists of two Spin-Lock (SL) pulses of duration $\tau$, separated by a $\pi$ pulse.
- The MW spin-lock frequency ($\Omega_{SL}$) is precisely tuned to satisfy the Generalized Hartmann-Hahn condition ($\Omega_{SL} \approx k \omega_f \pm \omega_n$), facilitating efficient electron-to-nucleus spin transfer.
- Noise Decoupling Mechanism: The periodic $\pi$ pulses within the rNOVEL sequence refocus the system dynamics, effectively decoupling the NV spin from external, low-frequency dephasing noise $b(t)$ (analogous to the Carr-Purcell-Meiboom-Gill, CPMG, sequence structure).
- Detection: A final detection MW pulse and subsequent laser pulse are used for optical detection of the resulting NV electronic spin state, which correlates with the nuclear polarization achieved.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe development and deployment of advanced quantum control sequences like rNOVEL require ultra-high-quality, highly controlled MPCVD diamond substrates. 6CCVD is uniquely positioned to supply the materials necessary to replicate, optimize, and scale this quantum sensing research.
Applicable Materials
Section titled âApplicable Materialsâ| Research Requirement | 6CCVD Material Recommendation | Technical Rationale & Benefit |
|---|---|---|
| High Spin Coherence | Optical Grade Single Crystal Diamond (SCD) | Ultra-low nitrogen impurity (PPM level) ensures minimal background paramagnetic defects, maximizing $T_2$ coherence time for efficient polarization transfer over long sequences (high $N$). |
| Controlled Nuclear Species | Isotopically Enriched SCD (e.g., highly concentrated 13C) | While the paper uses a natural abundance model, enriched substrates dramatically increase the density of target nuclei, accelerating polarization transfer and improving sensitivity for bulk polarization applications. |
| Shallow NV Creation | Polycrystalline Diamond (PCD) or SCD Substrates | If the goal is creating shallow NVs for nanodiamond or surface sensing (as suggested by the noise model), we offer substrates designed for optimal ion implantation and annealing. |
| Sensing/Micro-Fabrication | Custom Thin SCD Layers (0.1 ”m to 500 ”m) | Thin layers are crucial for integration into micro-structured devices or specialized MW resonators, maximizing NV density near the detection volume. |
Customization Potential
Section titled âCustomization PotentialâThe deployment of low-field NV-based quantum sensors often necessitates tailored materials for device integration, leveraging 6CCVDâs unique in-house engineering and fabrication services:
- Precision Polishing for Shallow NVs: The noise model used in the paper mimics shallow NVs (depth ~3 nm), which are highly sensitive to surface quality. 6CCVD provides ultra-low roughness polishing (Ra < 1 nm for SCD, < 5 nm for inch-size PCD), crucial for minimizing decoherence caused by surface defects.
- Custom Wafer Dimensions: We manufacture diamond plates and wafers up to 125 mm (PCD) in diameter, allowing for large-scale device fabrication and parallel testing of rNOVEL sequences.
- Integrated Microwave Circuitry: Successful spin manipulation requires robust MW delivery. 6CCVD offers internal metalization capabilities including deposition of Au, Pt, Pd, Ti, W, and Cu for creating integrated MW transmission lines and planar antenna structures directly on or beneath the diamond surface.
- Advanced Shaping and Cutting: We provide custom laser cutting and shaping to produce complex geometries required for micro-antennas or specialized packaging compatible with low-field magnetic systems.
Engineering Support
Section titled âEngineering SupportâThe enhanced noise resilience and low-field requirement of the rNOVEL sequence make it highly relevant for commercial quantum sensing and portable MRI initiatives. 6CCVDâs in-house PhD team provides specialized assistance:
- Material Selection for Sensing: Our experts can assist researchers in selecting the optimal diamond type (SCD vs. PCD, enrichment level, crystal orientation) to maximize the NV $T_2$ time for low-field sensing applications.
- Surface Preparation Optimization: We offer consultation on surface termination and post-growth processing to optimize substrates specifically for shallow NV creation and noise mitigation, directly addressing the noise models discussed in this research.
- Integration Consultation: Technical guidance is available for coupling the diamond materials with microwave circuits and optical systems necessary to implement the rNOVEL pulse sequence effectively.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
It was recently demonstrated that bulk nuclear polarization can be obtained using nitrogen vacancy (NV) color centers in diamonds, even at ambient conditions. This is based on the optical polarization of the NV electron spin, and using several polarization transfer methods. One such method is the nuclear orientation via electron spin locking (NOVEL) sequence, where a spin-locked sequence is applied on the NV spin, with a microwave power equal to the nuclear precession frequency. This was performed at relatively high fields, to allow for both polarization transfer and noise decoupling. As a result, this scheme requires accurate magnetic field alignment in order preserve the NV properties. Such a requirement may be undesired or impractical in many practical scenarios. Here we present a new sequence, termed the refocused NOVEL, which can be used for polarization transfer (and detection) even at low fields. Numerical simulations are performed, taking into account both the spin Hamiltonian and spin decoherence, and we show that, under realistic parameters, it can outperform the NOVEL sequence.