Microscopic Study of Optically Stable Coherent Color Centers in Diamond Generated by High-Temperature Annealing
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-08-16 |
| Journal | Physical Review Applied |
| Authors | King Cho Wong, San Lam Ng, Kin On Ho, Yang Shen, Jiahao Wu |
| Institutions | Hong Kong University of Science and Technology, Chinese University of Hong Kong |
| Citations | 12 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a novel, implantation-free High-Temperature Annealing (HTA) approach for creating high-quality, coherent Nitrogen Vacancy (NV) centers in diamond, simultaneously improving the host materialâs quantum properties.
- Implantation-Free Creation: The HTA method (1700°C) utilizes thermal activation and migration of existing vacancies and nitrogen dopants, avoiding the lattice damage and noise sources inherent in traditional ion implantation techniques.
- High Yield in Ultra-Pure Diamond: In ultra-low-nitrogen (3 ppb) diamond, the NV center yield achieved is greater than 17%, resulting in a concentration of 0.5 ppb (greater than 1 center per 5 ”m3), ideal for quantum computing and communication applications.
- Fourier-Transform-Limited Optics: Created single NV centers exhibit excellent spectral stability, with Fourier-transform-limited linewidths as low as 24 MHz and no observable spectral diffusion or charge state switching.
- Significant Coherence Improvement (T2): For high-nitrogen ensemble samples (100 ppm N), HTA resulted in a 3.3-fold increase in electron spin coherence time (T2).
- Spin Bath Reconfiguration: The improvement is attributed to defect reformation, specifically a massive reduction in paramagnetic P1 centers (substitutional nitrogen) by up to 83% (in 100 ppm N samples), converting them into spinless defects (like H3) or NV centers, thereby reducing spin noise.
- Enhanced Sensitivity: The combined effect of increased NV concentration and improved T2 time leads to an estimated 3.6-fold improvement in quantum sensing sensitivity compared to naturally grown samples.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| HTA Peak Temperature | 1700 | °C | Held for 30 minutes under vacuum. |
| HTA Ramp-Up Rate | 45 | °C/min | Heating rate to 1700 °C. |
| HTA Cool-Down Rate | -30 | °C/min | Cooling rate to ambient temperature (RT). |
| NV Center Yield | > 17 | % | Achieved in ultra-low [N] (3 ppb) diamond. |
| NV Concentration (Low [N]) | > 1 per 5 | ”m3 | Corresponds to 0.5 ppb in PPB-B sample. |
| Single NV Linewidth (Min) | 24 | MHz | Fourier transform-limited, measured via PLE. |
| Single NV Linewidth (Max) | < 50 | MHz | Observed across all 18 NVs tested in PPB-M membrane. |
| T2* (Low [N] Single NV) | 3.04 ± 0.91 | ”s | Sample PPB-B (13C spin bath limited). |
| T2 (Low [N] Single NV) | 0.66 ± 0.46 | ms | Sample PPB-B (13C spin bath limited). |
| T2 Improvement Factor | 3.3 | x | Ensemble sample HPHT100 (100 ppm N). |
| T2 Improvement Factor | 1.1 | x | Ensemble sample CVD1 (1 ppm N). |
| P1 Concentration Reduction (HPHT100) | ~83 | % | Reduced to ~17% of original value (100 ppm N sample). |
| P1 Concentration Reduction (CVD1) | ~16 | % | Reduced to ~84% of original value (1 ppm N sample). |
| H3 PL Intensity Increase | ~2 | x | Confirms conversion of P1/V into spinless defects. |
| Sensitivity Improvement | ~3.6 | x | Estimated for HPHT100 ensemble over raw samples. |
| Nitrogen Concentration (PPB-B/M) | < 3 | ppb | Ultra-low nitrogen samples. |
| Nitrogen Concentration (CVD1) | 1 | ppm | Dilute nitrogen sample. |
| Nitrogen Concentration (HPHT100) | 100 | ppm | High nitrogen sample. |
Key Methodologies
Section titled âKey MethodologiesâThe High-Temperature Annealing (HTA) process is an implantation-free method designed to activate existing defects and vacancies within the diamond lattice, followed by comprehensive characterization of the resulting NV centers and spin bath environment.
HTA Protocol (Creation Recipe)
Section titled âHTA Protocol (Creation Recipe)â- Furnace Environment: High-temperature furnace (Thermal Technology 1000-2560-FP20) under vacuum (~1 mbar) purged with Argon (Ar).
- Ramp-Up: Temperature increased from room temperature (RT) to 1700 °C at a rate of 45 °C/min.
- Hold Time: Temperature held constant at 1700 °C for 30 minutes.
- Cool-Down: System quickly cooled down to ambient temperature at a rate of -30 °C/min.
- Post-Processing: Samples subjected to a boiling acid treatment (perchloric acid : nitric acid : sulfuric acid = 1:1:1) to remove graphitized surface layers.
Characterization Techniques
Section titled âCharacterization Techniquesâ| Technique | Purpose | Key Findings |
|---|---|---|
| Confocal Microscopy (PL) | Imaging and quantifying NV center creation and concentration increase. | Confirmed uniform increase of [NV] in the bulk; quantified PL increase (up to 4x). |
| Photoluminescence Excitation (PLE) | Measuring optical excited-state structure and spectral stability. | Confirmed Fourier-transform-limited linewidths (24 MHz) and high spectral stability (no diffusion/switching). |
| Optically Detected Magnetic Resonance (ODMR) | Measuring electron spin properties (T1, T2, T2*). | Quantified T2 enhancement (up to 3.3x) and confirmed no microscopic noise introduction in low [N] samples. |
| Double Electron-Electron Resonance (DEER) | Probing local concentration of paramagnetic defects (P1 centers). | Verified significant reduction of [P1] (up to 83%) correlating with T2 improvement. |
| Optical Emission Spectra (405-nm excitation) | Identifying spinless defects (e.g., H3 centers). | Confirmed H3 PL intensity increase (~2x), supporting P1 conversion into spinless defects. |
Commercial Applications
Section titled âCommercial ApplicationsâThe HTA method produces high-quality, spectrally stable NV centers in large quantities within bulk diamond, making it highly relevant for scaling up quantum technologies.
| Application Area | Relevance of HTA Technology |
|---|---|
| Quantum Computing & Communication | HTA creates NV centers with long T2 times and stable optical properties, essential for reliable spin initialization, control, and entanglement generation (quantum nodes). |
| Quantum Sensing (Magnetometry/Thermometry) | The 3.6x improvement in sensitivity (due to increased [NV] and T2) enhances the performance of ensemble NV sensors for measuring magnetic fields, electric fields, and temperature. |
| Integrated Photonics & Nanophotonics | The ability to create high-quality NV centers at controlled depths (when combined with delta doping) is ideal for fabricating high-performance optical cavities and solid immersion lenses (SILs). |
| Solid-State Qubit Manufacturing | This implantation-free, thermal-activation approach is general and adaptable for mass production of vacancy-based quantum systems in other host materials with similar lattice structures, such as Silicon Carbide (SiC). |
| High-Purity Diamond Substrates | The method allows for the creation of high-density, high-quality qubits in ultra-low-nitrogen CVD diamond, which is otherwise nearly empty of usable NV centers post-growth. |
View Original Abstract
Single color centers in solid have emerged as promising physical platforms for quantum information science. Creating these centers with excellent quantum properties is a key foundation for further technological developments. In particular, the microscopic understanding of the spin-bath environments is the key to engineer color centers for quantum control. In this work, we propose and demonstrate a distinct high-temperature annealing (HTA) approach for creating high-quality nitrogen vacancy (N-V) centers in implantation-free diamonds. Simultaneously using the created N-V centers as probes for their local environment we verify that no damage is microscopically induced by the HTA. Nearly all single N-V centers created in ultralow-nitrogen-concentration membranes possess stable and Fourier-transform-limited optical spectra. Furthermore, HTA strongly reduces noise sources naturally grown in ensemble samples, and leads to more than threefold improvements of decoherence time and sensitivity. We also verify that the vacancy activation and defect reformation, especially H3 and P1 centers, can explain the reconfiguration between spin baths and color centers. This distinct approach will become a powerful tool in vacancy-based quantum technology. © 2022 American Physical Society.