Ultra-high strained diamond spin register with coherent optical control
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-06-03 |
| Journal | npj Quantum Information |
| Authors | Marco Klotz, Andreas Tangemann, Alexander Kubanek |
| Analysis | Full AI Review Included |
Ultra-High Strained Diamond Spin Registers: 6CCVD Technical Analysis
Section titled âUltra-High Strained Diamond Spin Registers: 6CCVD Technical AnalysisâThis document analyzes the recent findings regarding ultra-high strained Silicon Vacancy (SiV-) centers in nanodiamonds and outlines how 6CCVDâs expertise in high-purity, large-area MPCVD diamond materials and custom fabrication services can accelerate the transition of this research into scalable quantum technologies.
Executive Summary
Section titled âExecutive Summaryâ- Three-Qubit Register Demonstrated: Successful coherent control and characterization of a three-qubit register comprising the SiV electron spin, its optical dipole, and a nearby 13C nuclear spin.
- Phonon Mitigation via Strain: Ultra-high static strain ($\Delta_{gs}/2\pi \approx 1.111 \text{ THz}$) enabled operation at elevated temperatures ($T > 2.6 \text{ K}$) while suppressing phonon-induced dephasing.
- Exceptional Coherence: Achieved an electron spin coherence time ($T_{2,e}$) of $273 \text{ ”s}$ (CPMG-64) and a nuclear spin coherence time ($T_{2,n}$) of $1.17 \text{ ms}$, comparable to or exceeding previous reports for Group-IV centers at liquid helium temperatures.
- High-Fidelity Control: Demonstrated single-qubit gate fidelity ($F_{G}$) of $0.9949(45)$ and coherent optical control of the SiV dipole with Rabi frequencies exceeding $1 \text{ GHz}$.
- Scalability Pathway: The results validate strain-engineered SiV centers as robust, optically accessible qubits suitable for integration into conventional photonics and hybrid quantum communication systems.
- 6CCVD Advantage: 6CCVD provides the necessary high-purity Single Crystal Diamond (SCD) substrates and custom metalization services required for deterministic strain engineering and scalable device integration.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the research paper, highlighting the performance metrics achieved using the ultra-high strained SiV center.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| SiV Ground-State Splitting ($\Delta_{gs}/2\pi$) | 1111(86) | GHz | Result of ultra-high static strain |
| Operating Temperature (T) | > 2.6 | K | Elevated temperature operation |
| Electron Spin Dephasing Time ($T_{2,e}$) | 4.67(30) | ”s | Measured via Ramsey interference |
| Electron Spin Coherence Time ($T_{2,e}$) | 273(15) | ”s | Measured via CPMG-64 dynamical decoupling |
| Nuclear Spin Coherence Time ($T_{2,n}$) | 1.17(16) | ms | Limited by electron spin relaxation ($T_{1,e}$) |
| Single-Qubit Gate Fidelity ($F_{G}$) | 0.9949(45) | - | Extracted from Randomized Benchmarking |
| Optical Rabi Frequency ($\Omega_{R,\gamma}/2\pi$) | 1.144(25) | GHz | Coherent optical control |
| Microwave Rabi Frequency ($\Omega_{R}/2\pi$) | Up to 10 | MHz | Electron spin control |
| 13C Hyperfine Coupling ($A_{\parallel}/2\pi$) | 621.8(42) | kHz | Parallel interaction strength |
| Microwave Waveguide Thickness (Au) | 200 | nm | Fabricated on sapphire substrate |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relied on precise material preparation, advanced microwave engineering, and high-speed optical control techniques:
- Material Synthesis: Nanodiamonds containing SiV centers were synthesized using a High-Pressure/High-Temperature (HPHT) process (8 GPa, 1450 °C).
- Substrate and Waveguide: Nanodiamonds were placed on a sapphire substrate (chosen for thermal conductivity). A coplanar microwave waveguide was fabricated using optical lithography, electron-beam metal deposition, and lift-off, consisting of a 200 nm Gold (Au) layer over a 20 nm Titanium (Ti) adhesion layer.
- Magnetic Field: A static magnetic field ($B_{0}$) was supplied by four N52 neodymium permanent magnets in a Hallbach configuration, buried in the cold finger.
- Microwave Control: Microwave pulses were synthesized using a 65 GS/s Arbitrary Waveform Generator (AWG), amplified, and sent to the cryostat, enabling coherent electron spin driving up to $10 \text{ MHz}$ Rabi frequency.
- Coherent Optical Control: An Electro-Optical Modulator (EOM) was used to generate sub-nanosecond optical sideband pulses, which were filtered by two etalons (FWHM $1.7 \text{ GHz}$) to suppress the laser carrier, achieving $\text{GHz}$ Rabi frequencies.
- Coherence Extension: Dynamical Decoupling (DD) sequences, specifically CPMG-N (up to N=64), were applied to the electron spin to extend $T_{2,e}$ coherence time.
- Single-Shot Nuclear Readout (SSR): A CNOT gate sequence was combined with a short laser pulse ($T_{p} \approx 10 \text{ ”s}$) and repeated ($N_{SSR}$ times) to achieve single-shot discrimination of the 13C nuclear spin state based on mean-photon number statistics.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe research successfully demonstrated the potential of strain-engineered SiV centers. However, scaling this technology requires moving from non-deterministically placed nanodiamonds to large-area, high-purity Single Crystal Diamond (SCD) wafers. 6CCVD is uniquely positioned to supply the necessary materials and fabrication services to transition this research to integrated quantum devices.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate and extend this research into scalable integrated quantum circuits, 6CCVD recommends:
- Optical Grade Single Crystal Diamond (SCD): Required for deterministic SiV creation and precise strain engineering. Our SCD features extremely low nitrogen concentration (< 1 ppb N), minimizing spin bath noise and maximizing intrinsic coherence times ($T_{2}$).
- Custom Silicon Doping: We offer controlled, high-uniformity silicon doping during MPCVD growth to ensure high density and quality of SiV centers.
- Thick SCD Substrates: SCD plates up to $500 \text{ ”m}$ thick are available, providing robust platforms for applying the ultra-high static strain necessary to achieve $\text{THz}$ ground-state splitting.
Customization Potential
Section titled âCustomization PotentialâThe paper utilized specific dimensions and metalization for microwave delivery. 6CCVD offers comprehensive customization to meet these engineering demands:
| Research Requirement | 6CCVD Customization Service | Technical Advantage |
|---|---|---|
| Substrate Dimensions | Custom SCD plates/wafers up to $125 \text{ mm}$ (PCD) and $500 \text{ ”m}$ thick (SCD). | Enables wafer-scale fabrication and integration with established silicon photonics platforms. |
| Microwave Waveguide (Ti/Au) | In-House Metalization: Deposition of Ti (adhesion layer) and Au (conductor), as well as Pt, Pd, W, or Cu. | Provides ready-to-use, patterned diamond substrates optimized for high-frequency microwave delivery and low heat load. |
| Surface Quality | Precision Polishing: SCD surfaces polished to ultra-low roughness ($R_{a} < 1 \text{ nm}$). | Essential for minimizing optical losses when integrating SiV centers with high-Q photonic cavities (e.g., etalons or waveguides). |
| Laser Processing | Custom Laser Cutting/Dicing: Precise shaping and dicing of SCD wafers to create specific geometries for mechanical strain application or device integration. | Supports complex device architectures required for deterministic strain control. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house team of PhD material scientists specializes in defect engineering and material optimization for quantum applications. We offer consultation on:
- Deterministic Strain Engineering: Assisting researchers in selecting the optimal SCD thickness and geometry for applying uniform, ultra-high strain fields, moving beyond the non-deterministic strain found in nanodiamonds.
- Material Selection: Guidance on selecting the appropriate SCD grade and doping level to maximize SiV yield and coherence for similar quantum network register projects.
- Integration Strategy: Support for integrating metalized diamond structures with cryostat environments and high-speed microwave/optical systems.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Solid-state spin defects, such as color centers in diamond, are among the most promising candidates for scalable and integrated quantum technologies. In particular, the good optical properties of silicon-vacancy centers in diamond, combined with naturally occurring and exceptionally coherent nuclear spins, serve as a building block for quantum networking applications. Here, we show that leveraging an ultra-high-strained silicon-vacancy center inside a nanodiamond allows us to coherently and efficiently control its electron spin, while mitigating phonon-induced dephasing at liquid helium temperature. Moreover, we indirectly control and characterize a 13 C nuclear spin and establish a quantum register. We overcome limited nuclear spin initialization by implementing single-shot nuclear spin readout. Lastly, we demonstrate coherent optical control with GHz rates, thus opening a potential connection of the register to the optical domain. Our work paves the way for future integration of quantum network registers into conventional, well-established photonics and hybrid quantum communication systems.