Control of Solid-State Nuclear Spin Qubits Using an Electron Spin-1/2
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2025-04-11 |
| Journal | Physical Review X |
| Authors | Hans K. C. Beukers, Christopher Waas, M. Pasini, Hendrik B. van Ommen, Zarije Ademi |
| Institutions | Delft University of Technology |
| Citations | 2 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Enhanced Nuclear Spin Control in Diamond SnV Centers
Section titled āTechnical Documentation & Analysis: Enhanced Nuclear Spin Control in Diamond SnV CentersāExecutive Summary
Section titled āExecutive SummaryāThis research successfully demonstrates advanced control over solid-state nuclear spin qubits (specifically 13C) utilizing the electron spin-1/2 of a diamond Tin-Vacancy (SnV) center. The findings are critical for scaling quantum registers based on Group-IV color centers.
- Enhanced Selectivity: The study pioneers the use of Dynamically Decoupled Radio-Frequency (DDRF) gates, proving superior selectivity and control over nuclear spins compared to standard Dynamical Decoupling (DD) methods, especially crucial for electron spin-1/2 systems.
- High-Fidelity Entanglement: Achieved high-fidelity entanglement between the SnV electron spin and a nearby 13C nuclear spin, yielding a Bell state fidelity of 72(3)%.
- Long Coherence Times: Demonstrated robust electron spin coherence (T2DD = 1.7(5) ms) and long nuclear spin memory (T2* = 17.2(6) ms) at 0.4 K, confirming the SnV centerās viability as a quantum memory node.
- Material Requirement Insight: The observed electron coherence is limited by the electron spin bath, suggesting that future high-fidelity experiments require ultra-low defect density diamond, achievable through high-purity Chemical Vapor Deposition (CVD) growth.
- Applicability: The DDRF method and control insights directly translate to other promising electron spin-1/2 platforms, including Silicon-Vacancy (SiV) and Germanium-Vacancy (GeV) centers, and rare-earth ions.
Technical Specifications
Section titled āTechnical SpecificationsāThe following hard data points were extracted from the experimental characterization of the SnV quantum register:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Host Material | CVD Diamond | N/A | Natural 1.1% 13C abundance |
| Qubit Center | Negatively Charged Tin-Vacancy (SnV-) | N/A | Effective electron spin-1/2 system |
| Operating Temperature | 0.4 | K | He cryostat base temperature |
| Bias Magnetic Field (BDC) | 0.1 | T | Aligned with SnV symmetry axis |
| Electron Spin Coherence (T2DD) | 1.7(5) | ms | Achieved using 256Ļ XY8 decoupling pulses |
| Nuclear Spin Coherence (T2*) | 17.2(6) | ms | Measured for 13C spin CB via Ramsey sequence |
| Electron Rabi Frequency (Ī©MW/2Ļ) | 2.46 | MHz | Microwave control |
| Electron Gate Fidelity | 98(2) | % | Measured via process tomography |
| Bell State Fidelity (FBell) | 72(3) | % | Electron-nuclear entanglement using DDRF |
| Sn Implantation Dose | 5 x 1010 | ions/cm2 | Target depth 88 nm |
| Optical Transition Wavelength | 619 | nm | Initialization and readout laser |
| Average Readout Fidelity | 77.7(3) | % | Single-shot readout |
| Parallel Hyperfine Difference (ĪA||) | -404(2) | kHz | Excited state vs. ground state coupling |
Key Methodologies
Section titled āKey MethodologiesāThe experimental control and characterization relied on precise material preparation and advanced quantum control sequences:
- Material Synthesis and Implantation: Experiments were performed on CVD-grown diamond implanted with spinless 120Sn ions (5 x 1010 ions/cm2 dose) and subsequently annealed at 1100 Ā°C to form SnV centers.
- Cryogenic and Magnetic Environment: The sample was cooled to 0.4 K in a He cryostat. A bias magnetic field of 0.1 T was applied, aligned with the SnV center symmetry axis.
- Optical Qubit Interface: The electron spin was initialized and read out optically using a 619 nm laser, leveraging spin-selective optical excitation for single-shot readout.
- Electron Coherence Protection: Dynamical Decoupling (DD) sequences (specifically XY8) were applied via microwave driving to extend the electron spin coherence time (T2) and protect it from the surrounding spin bath noise.
- Dynamical Decoupling (DD) Control: Nuclear spin control was achieved by tuning the interpulse delay (Ļ) of the DD sequence to resonate with the nuclear spin dynamics, enabling conditional rotation (CNOT-equivalent gate).
- Dynamically Decoupled Radio-Frequency (DDRF) Control: This improved method combined DD coherence protection with direct radio-frequency (rf) driving of the nuclear spin. A tailored phase update rule (Ī“Ļ = 2Ļįæ¶ + Ļ) was used to achieve conditional rotation and enhance selectivity, successfully controlling a 13C spin (CB) previously insensitive to DD.
- Entanglement Protocol: Electron-nuclear entanglement was generated using Measurement-Based Initialization (MBI) of the nuclear spin, followed by the optimized DDRF two-qubit gate.
6CCVD Solutions & Capabilities
Section titled ā6CCVD Solutions & CapabilitiesāThis research highlights the critical role of high-quality diamond material and precise fabrication in achieving high-fidelity solid-state quantum control. 6CCVD is uniquely positioned to supply the materials and processing required to replicate, extend, and scale this SnV-based quantum register technology.
Applicable Materials
Section titled āApplicable MaterialsāTo replicate or extend this research, particularly addressing the decoherence limitations noted in the paper (attributed to the electron spin bath), the following 6CCVD materials are required:
| Material Grade | Specification & Application | 6CCVD Advantage |
|---|---|---|
| Optical Grade SCD | Ultra-Low Defect Density: SCD with nitrogen concentration < 1 ppb and controlled isotopic purity (< 0.01% 13C) is essential to minimize the electron spin bath noise and maximize T2 coherence, enabling higher gate fidelities. | Industry-Leading Purity: Directly addresses the T2 limitation cited in the paper, providing the lowest noise environment for Group-IV centers (SnV, SiV, GeV). |
| Isotopically Engineered SCD | 13C Enriched or Depleted: Custom SCD wafers with specific 13C concentrations to either enhance the nuclear spin memory register (enriched) or eliminate the nuclear spin bath entirely (depleted). | Precise Control: Allows researchers to tailor the nuclear spin environment for optimal qubit register design, supporting multiqubit scaling. |
| SCD Substrates | High-Quality, Thick Platforms: SCD substrates up to 500 Āµm thick, or custom substrates up to 10 mm, providing robust platforms for high-energy ion implantation and subsequent annealing. | Dimensional Flexibility: Supports deep implantation profiles and robust mechanical integration into cryogenic setups. |
Customization Potential
Section titled āCustomization PotentialāThe complexity of the experimental setup, involving precise magnetic field alignment and RF/MW delivery, necessitates advanced material customization:
- Custom Dimensions and Orientation: 6CCVD supplies SCD plates with precise (100) orientation (as used in the paper) and custom dimensions up to 125mm (PCD) to fit specific cryostat or integration requirements.
- Ultra-Smooth Polishing: Our SCD polishing capability achieves surface roughness Ra < 1 nm, critical for minimizing surface defects that can contribute to decoherence and ensuring high-quality optical coupling for the 619 nm laser interface.
- Integrated Metalization and Patterning: The experiment requires precise delivery of MW and RF signals. 6CCVD offers internal metalization services (e.g., Ti/Pt/Au, Cu, W) for depositing and patterning on-chip microwave waveguides or antennas directly onto the diamond surface, improving coupling efficiency and control fidelity.
- Laser Cutting and Shaping: We offer precision laser cutting for creating custom geometries, trenches, or features necessary for integrating the diamond into nanophotonic or waveguide structures (as referenced in the SnV literature).
Engineering Support
Section titled āEngineering Supportā6CCVD is more than a material supplier; we are a technical partner. Our in-house PhD team specializes in the material science of quantum defects:
- We offer consultation on optimizing diamond specifications (purity, strain, orientation) to maximize T2 coherence for similar Group-IV color center (SnV, SiV, GeV) projects.
- We assist in defining optimal implantation parameters (dose, energy, annealing protocols) to achieve high-yield, low-strain SnV centers suitable for high-fidelity DDRF control.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Solid-state quantum registers consisting of optically active electron spins with nearby nuclear spins are promising building blocks for future quantum technologies. For electron spin-1 registers, dynamical decoupling (DD) quantum gates have been developed that enable the precise control of multiple nuclear spin qubits. However, for the important class of electron spin-<a:math xmlns:a=āhttp://www.w3.org/1998/Math/MathMLā display=āinlineā><a:mrow><a:mn>1</a:mn><a:mo>/</a:mo><a:mn>2</a:mn></a:mrow></a:math> systems, this control method suffers from intrinsic selectivity limitations, resulting in reduced nuclear spin gate fidelities. Here, we demonstrate improved control of single nuclear spins by an electron spin-<c:math xmlns:c=āhttp://www.w3.org/1998/Math/MathMLā display=āinlineā><c:mrow><c:mn>1</c:mn><c:mo>/</c:mo><c:mn>2</c:mn></c:mrow></c:math> using dynamically decoupled radio-frequency (DDRF) gates. We make use of the electron spin-<e:math xmlns:e=āhttp://www.w3.org/1998/Math/MathMLā display=āinlineā><e:mrow><e:mn>1</e:mn><e:mo>/</e:mo><e:mn>2</e:mn></e:mrow></e:math> of a diamond tin-vacancy center, showing high-fidelity single-qubit gates, single-shot readout, and spin coherence beyond a millisecond. The DD control is used as a benchmark to observe and control a single <g:math xmlns:g=āhttp://www.w3.org/1998/Math/MathMLā display=āinlineā><g:mrow><g:mmultiscripts><g:mrow><g:mn>3</g:mn></g:mrow><g:mprescripts/><g:none/><g:mrow><g:mn>1</g:mn></g:mrow></g:mmultiscripts><g:mi mathvariant=ānormalā>C</g:mi></g:mrow></g:math> nuclear spin. Using the DDRF control method, we demonstrate improved control on that spin. In addition, we find and control an additional nuclear spin that is insensitive to the DD control method. Using these DDRF gates, we show entanglement between the electron and the nuclear spin with 72(3)% state fidelity. Our extensive simulations indicate that DDRF gate fidelities well in excess are feasible. Finally, we employ time-resolved photon detection during readout to quantify the hyperfine coupling for the electronās optically excited state. Our work provides key insights into the challenges and opportunities for nuclear spin control in electron spin-<j:math xmlns:j=āhttp://www.w3.org/1998/Math/MathMLā display=āinlineā><j:mrow><j:mn>1</j:mn><j:mo>/</j:mo><j:mn>2</j:mn></j:mrow></j:math> systems, opening the door to multiqubit experiments on these promising qubit platforms.