Silicon-Vacancy Spin Qubit in Diamond - A Quantum Memory Exceeding 10 ms with Single-Shot State Readout
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2017-11-29 |
| Journal | Physical Review Letters |
| Authors | Denis D. Sukachev, Alp Sipahigil, C. T. Nguyen, Mihir K. Bhaskar, Ruffin E. Evans |
| Institutions | Harvard University, Center for Integrated Quantum Science and Technology |
| Citations | 420 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Silicon-Vacancy Spin Qubit in Diamond
Section titled “Technical Documentation & Analysis: Silicon-Vacancy Spin Qubit in Diamond”Executive Summary
Section titled “Executive Summary”This research establishes the Silicon-Vacancy ($\text{SiV}^-$) center in diamond as a leading solid-state platform for quantum networks by demonstrating unprecedented spin coherence and relaxation times under cryogenic conditions.
- Record Coherence: Achieved a spin coherence time ($T_2$) of 13 ms and a spin relaxation time ($T_1$) exceeding 1 s, extending previous records by five orders of magnitude.
- Phonon Suppression: Demonstrated effective suppression of phonon-induced dephasing by operating the system at temperatures below 500 mK (minimum 100 mK).
- High Fidelity Readout: Achieved high-fidelity, single-shot readout of the $\text{SiV}^-$ spin state with an average fidelity of 89%.
- Material Requirements: Success relied on ultra-pure, low-strain Type-IIa diamond substrates, specifically engineered with low $^{13}\text{C}$ isotopic abundance ($10^{-3}%$) to mitigate nuclear spin bath decoherence.
- Methodology: Coherence extension utilized Carr-Purcell-Meiboom-Gill (CPMG) dynamical decoupling sequences (up to N=32 pulses) and efficient microwave control via coplanar waveguides.
- Application: These results meet the memory lifetime requirements necessary for quantum repeater nodes separated by distances up to $10^3$ km.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the research detailing the performance and material parameters required for the $\text{SiV}^-$ spin qubit.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Spin Coherence Time ($T_2$) | 13 ± 1.7 | ms | Longest observed, N=32 CPMG pulses, 100 mK |
| Spin Relaxation Time ($T_1$) | > 1 | s | Measured at 100 mK |
| Operating Temperature | 100 | mK | Minimum temperature achieved in dilution refrigerator |
| Dephasing Suppression | 5 orders of magnitude | N/A | Achieved by operating below 500 mK |
| Single-Shot Readout Fidelity | 89 | % | Average fidelity |
| Magnetic Field (B) | 2.7 | kG | Used for single-shot spin readout |
| SiV Center Depth | ~ 250 | nm | Target depth via $^{28}\text{Si}$ ion implantation |
| Implantation Dose | $10^9$ | cm-2 | Used for single $\text{SiV}^-$ center creation |
| Implantation Energy | 380 | keV | Used for $^{28}\text{Si}$ ions |
| Diamond Purity (Nitrogen) | < 5 | ppb | Type-IIa substrate requirement |
| Diamond Purity (Boron) | < 1 | ppb | Type-IIa substrate requirement |
| Low $^{13}\text{C}$ Abundance (Sample 12) | $10^{-3}$ | % | Engineered isotopic purity to suppress nuclear spin bath |
Key Methodologies
Section titled “Key Methodologies”The successful demonstration of long-lived $\text{SiV}^-$ coherence relied on precise material engineering and advanced cryogenic control techniques.
- Substrate Selection: Utilized ultra-pure Type-IIa diamond (Nitrogen < 5 ppb, Boron < 1 ppb) to minimize background defects. Crucially, one sample (Sample 12) was isotopically engineered to have only $10^{-3}% \text{ }^{13}\text{C}$ abundance to suppress hyperfine interactions.
- Color Center Creation: Single $\text{SiV}^-$ centers were created via $^{28}\text{Si}$ ion implantation at 380 keV energy and a low dose of $10^9 \text{ cm}^{-2}$, followed by high-temperature annealing.
- Microwave (MW) Integration: A shorted coplanar waveguide was fabricated directly onto the diamond surface to efficiently deliver MW fields for coherent control of the qubit states.
- Cryogenic Environment: The diamond sample was mounted in a dilution refrigerator and placed inside a superconducting vector magnet, allowing for operation at 100 mK to decouple the electronic spin from the thermal acoustic phonon bath.
- Spin Manipulation: Pulsed optically-detected magnetic resonance (ODMR) was used to determine the qubit frequency ($f_{\uparrow\downarrow}$) and drive Rabi oscillations between the spin states.
- Coherence Extension: Dynamical decoupling sequences, specifically Carr-Purcell-Meiboom-Gill (CPMG) sequences with up to 32 rephasing $\pi$-pulses, were implemented to suppress dephasing caused by slowly evolving environmental fluctuations.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”6CCVD is uniquely positioned to supply the high-purity, custom-engineered MPCVD diamond required to replicate, extend, and integrate this groundbreaking $\text{SiV}^-$ research into scalable quantum devices.
Applicable Materials
Section titled “Applicable Materials”To achieve the demonstrated coherence times, the research requires diamond with extremely low strain and high isotopic purity, which 6CCVD provides through its specialized MPCVD growth processes.
| Research Requirement | 6CCVD Material Solution | Key Capability Match |
|---|---|---|
| Ultra-low Impurity (Type-IIa) | Electronic Grade SCD | Nitrogen < 5 ppb, Boron < 1 ppb (standard specifications). |
| Isotopic Purity ($10^{-3}% \text{ }^{13}\text{C}$) | Custom Isotopic SCD | We offer SCD substrates with custom $^{13}\text{C}$ depletion (e.g., < 0.01%) to minimize nuclear spin bath decoherence. |
| Low Surface Roughness | Optical Grade SCD | Polishing capability to Ra < 1 nm, critical for integrated nanophotonics and waveguide coupling. |
| Large Area Substrates | PCD Wafers | For scaling up integrated quantum circuits, we offer PCD plates up to 125 mm in diameter. |
Customization Potential
Section titled “Customization Potential”The experiment required precise ion implantation and the fabrication of coplanar waveguides. 6CCVD offers comprehensive post-processing services to streamline the fabrication workflow for quantum engineers.
- Custom Metalization: The coplanar waveguides require high-quality metal contacts. 6CCVD offers in-house metalization services, including common waveguide materials such as Ti, Pt, Au, and Cu, applied with high precision.
- Custom Dimensions and Thickness: We supply SCD plates in thicknesses ranging from 0.1 µm up to 500 µm, and substrates up to 10 mm thick, allowing researchers to optimize for specific ion implantation depths (e.g., 250 nm) or nanophotonic device integration.
- Surface Preparation: We provide ultra-low damage polishing (Ra < 1 nm for SCD) essential for minimizing surface defects that can degrade the coherence of near-surface $\text{SiV}^-$ centers.
- Laser Cutting and Shaping: Custom laser cutting services are available to produce precise geometries required for mounting in cryogenic systems or for specific waveguide layouts.
Engineering Support
Section titled “Engineering Support”6CCVD’s in-house PhD team specializes in defect engineering and material optimization for quantum applications.
- Defect Optimization: We provide consultation on optimizing diamond growth parameters and post-processing (e.g., annealing recipes) to maximize the yield and quality of specific color centers, including $\text{SiV}^-$ and NV centers.
- Cryogenic Integration: Our experts can assist with material selection and preparation to ensure optimal thermal and mechanical performance in extreme cryogenic environments (down to 100 mK).
- Application Focus: We offer dedicated engineering support for projects focused on Quantum Networks, Integrated Diamond Photonics, and Solid-State Quantum Memory based on the $\text{SiV}^-$ platform.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
The negatively charged silicon-vacancy (SiV^{-}) color center in diamond has recently emerged as a promising system for quantum photonics. Its symmetry-protected optical transitions enable the creation of indistinguishable emitter arrays and deterministic coupling to nanophotonic devices. Despite this, the longest coherence time associated with its electronic spin achieved to date (∼250 ns) has been limited by coupling to acoustic phonons. We demonstrate coherent control and suppression of phonon-induced dephasing of the SiV^{-} electronic spin coherence by 5 orders of magnitude by operating at temperatures below 500 mK. By aligning the magnetic field along the SiV^{-} symmetry axis, we demonstrate spin-conserving optical transitions and single-shot readout of the SiV^{-} spin with 89% fidelity. Coherent control of the SiV^{-} spin with microwave fields is used to demonstrate a spin coherence time T_{2} of 13 ms and a spin relaxation time T_{1} exceeding 1 s at 100 mK. These results establish the SiV^{-} as a promising solid-state candidate for the realization of quantum networks.