Quantum Control of the Tin-Vacancy Spin Qubit in Diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-11-30 |
| Journal | Physical Review X |
| Authors | Romain Debroux, Cathryn P. Michaels, Carola M. Purser, Noel Wan, Matthew E. Trusheim |
| Institutions | DEVCOM Army Research Laboratory, University of Cambridge |
| Citations | 71 |
| Analysis | Full AI Review Included |
Technical Documentation: Quantum Control of the Tin-Vacancy (SnV) Spin Qubit in Diamond
Section titled âTechnical Documentation: Quantum Control of the Tin-Vacancy (SnV) Spin Qubit in DiamondâReference: Debroux et al., Quantum control of the tin-vacancy spin qubit in diamond, arXiv:2106.00723v1 [quant-ph] (2021).
Executive Summary
Section titled âExecutive SummaryâThe research successfully demonstrates all-optical, multi-axis coherent control of the negatively charged Tin-Vacancy (SnV-) spin qubit in diamond, establishing it as a highly competitive platform for quantum networking.
- All-Optical Control: Coherent control was achieved using an all-optical stimulated Raman drive, circumventing the inefficiency of direct microwave control previously observed in SnV centers.
- High-Speed Operation: Spin Rabi oscillations were measured at a rate of 3.6(1) MHz, representing a nearly three orders of magnitude improvement over previous direct microwave control attempts.
- Extended Coherence: Dynamical decoupling (CPMG-2) extended the spin coherence time (T2) to 0.33(14) ms, confirming the SnVâs robustness against phonon dephasing at 1.7 K.
- High Fidelity Gates: A Ï/2 gate fidelity of 92(4)% was achieved, limited primarily by optical scattering, indicating clear pathways for further improvement via increased laser power and detuning.
- Material Foundation: The work relies on high-purity, low-strain CVD diamond substrates, confirming the necessity of high-quality Single Crystal Diamond (SCD) for scaling group-IV quantum emitters.
- Quantum Network Potential: The results confirm the SnV centerâs promise as a robust spin-photon building block, leveraging its large spin-orbit coupling for strong protection against decoherence.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental results and material characterization:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Operating Temperature | 1.7 | K | Magneto-optical cryostat base temperature |
| Magnetic Field Strength (B) | 200 | mT | Applied at 54.7° relative to SnV symmetry axis |
| Optical Transition Wavelength | 619 | nm | Optical transition energy 484 THz |
| Ground State Spin-Orbit Splitting (ÎSO) | 850 | GHz | |
| Excited State Spin-Orbit Splitting (ÎSO) | 3000 | GHz | |
| Spin Rabi Oscillation Rate (Ω/2Ï) | 3.6(1) | MHz | Achieved via all-optical Raman drive |
| Inhomogeneous Dephasing Time (T2*) | 1.3(3) | ”s | Measured via Ramsey interferometry |
| Coherence Time (T2) | 0.33(14) | ms | Extended using CPMG-2 dynamical decoupling |
| Ï/2 Gate Fidelity | 92(4) | % | Limited by optical scattering |
| Hyperfine Coupling Strength (A) | 42.6(4) | MHz | For spin-active 115Sn, 117Sn, or 119Sn isotope |
| Substrate Purity | < 5 | ppb | Element6 CVD-grown Type IIa diamond [N], [B] |
| Sn+ Implantation Energy | 350 | keV | |
| Sn+ Implantation Fluence | 109 | ions/cm2 | |
| Nanopillar Radii | 75 to 165 | nm | Fabricated to improve fluorescence collection |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relied on high-precision material engineering and advanced optical control techniques:
- Substrate Preparation: High-purity Element6 CVD-grown Type IIa diamond (< 5 ppb N, B) was used as the starting material.
- SnV Creation: Sn+ ions were implanted at 350 keV with a fluence of 109 ions/cm2, resulting in a predicted dopant depth of 80(10) nm below the surface.
- Annealing and Cleaning: The sample was annealed at 1200 °C for two hours under high vacuum (< 10-7 mbar), followed by acid cleaning (boiling sulfuric, nitric, and perchloric acid mixture) to remove residual graphite.
- Nanostructure Fabrication: Nanopillars (radii 75 to 165 nm) were fabricated to enhance photon collection efficiency and isolate individual SnV centers.
- Qubit Initialization and Readout: Spin initialization (up to 99% fidelity) and readout were performed using resonant laser pulses (619 nm) driving the spin-cycling (A1) and spin-flipping (A2) transitions.
- Coherent Control: Multi-axis coherent control was achieved using an all-optical stimulated Raman drive, generated by passing a single-frequency laser through a microwave-modulated electro-optic modulator (EOM) to create two sidebands (Ï1, Ï2).
- Coherence Extension: Dynamical decoupling protocols (Hahn echo and CPMG-2) were implemented using sequences of optical Ï/2 pulses to suppress low-frequency magnetic noise from the 13C nuclear spin bath.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the foundational diamond materials and advanced processing required to replicate and scale the high-fidelity SnV quantum control demonstrated in this research.
Applicable Materials for SnV Qubit Research
Section titled âApplicable Materials for SnV Qubit ResearchâThe success of this experiment hinges on the use of ultra-low defect density diamond. 6CCVD offers materials optimized for quantum applications:
- Optical Grade Single Crystal Diamond (SCD): Required for high-coherence group-IV color centers. Our SCD material features extremely low nitrogen and boron concentrations (sub-ppb levels), minimizing background noise and maximizing T2 coherence times.
- Custom Substrate Thickness: The research utilized thin implantation depths (80 nm). 6CCVD provides SCD substrates with precise thickness control from 0.1 ”m up to 500 ”m, allowing researchers to optimize implantation and subsequent nanostructure etching processes.
- High-Quality Polishing: The integrity of the diamond surface is critical for subsequent ion implantation and nanopillar fabrication. 6CCVD guarantees Ra < 1 nm polishing on SCD wafers, ensuring minimal surface damage and strain that could degrade qubit performance.
Customization Potential for Scaling and Integration
Section titled âCustomization Potential for Scaling and IntegrationâTo transition SnV research from single emitters to integrated quantum circuits, 6CCVD provides comprehensive engineering services:
| Research Requirement | 6CCVD Capability | Technical Advantage |
|---|---|---|
| Large Area Substrates | Plates/wafers up to 125 mm (PCD) and large SCD plates. | Enables wafer-scale processing and high-throughput fabrication of photonic circuits and qubit arrays. |
| Nanostructure Support | Custom laser cutting and precision etching support. | Provides substrates pre-cut to specific geometries required for focused ion beam (FIB) or reactive ion etching (RIE) used in nanopillar fabrication. |
| Electrical Contacting | In-house metalization services: Au, Pt, Pd, Ti, W, Cu. | Essential for integrating SnV centers into electrical devices (e.g., for Stark shift control or electrical readout). We offer custom layer stacks and patterning. |
| Boron Doping (BDD) | SCD and PCD available with controlled Boron doping. | While not used here, BDD is critical for creating conductive diamond layers necessary for integrated microwave or electrical gates in future quantum devices. |
| Global Logistics | Global shipping (DDU default, DDP available). | Ensures rapid and reliable delivery of sensitive diamond materials worldwide, supporting international research collaborations. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house team of PhD material scientists and quantum engineers can assist researchers in optimizing material selection for similar Group-IV Color Center (SnV, SiV, GeV) Quantum Control projects. We specialize in tailoring diamond properties (purity, strain, surface termination) to maximize qubit performance and integration fidelity.
Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
<p>Group-IV color centers in diamond are a promising light-matter interface for quantum networking devices. The negatively charged tin-vacancy center (SnV) is particularly interesting, as its large spin-orbit coupling offers strong protection against phonon dephasing and robust cyclicity of its optical transitions toward spin-photon-entanglement schemes. Here, we demonstrate multiaxis coherent control of the SnV spin qubit via an all-optical stimulated Raman drive between the ground and excited states. We use coherent population trapping and optically driven electronic spin resonance to confirm coherent access to the qubit at 1.7 K and obtain spin Rabi oscillations at a rate of Ï/2Ï=19.0(1) MHz. All-optical Ramsey interferometry reveals a spin dephasing time of T2â=1.3(3) ÎŒs, and four-pulse dynamical decoupling already extends the spin-coherence time to T2=0.30(8) ms. Combined with transform-limited photons and integration into photonic nanostructures, our results make the SnV a competitive spin-photon building block for quantum networks.</p>