A Phononic Bus for Coherent Interfaces Between a Superconducting Quantum Processor, Spin Memory, and Photonic Quantum Networks
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-03-18 |
| Journal | arXiv (Cornell University) |
| Authors | Tomas Neuman, Matt Eichenfield, Matthew E. Trusheim, Lisa Hackett, Prineha Narang |
| Citations | 4 |
| Analysis | Full AI Review Included |
6CCVD Technical Documentation: Hybrid Quantum Transduction via Phononic Diamond Systems
Section titled â6CCVD Technical Documentation: Hybrid Quantum Transduction via Phononic Diamond SystemsâReference Paper: A Phononic Bus for Coherent Interfaces Between a Superconducting Quantum Processor, Spin Memory, and Photonic Quantum Networks
This technical documentation analyzes the requirements and achievements of the referenced research, focusing specifically on the demand for advanced MPCVD diamond materials necessary to realize high-fidelity, scalable hybrid quantum architectures.
Executive Summary
Section titled âExecutive SummaryâThis research establishes a theoretical and design framework for achieving high-fidelity quantum state transduction between disparate physical platformsâspecifically, Superconducting (SC) qubits and Silicon Vacancy ($\text{SiV}^-$) solid-state artificial atomsâusing a diamond-based phononic bus.
- Core Achievement: Numerical modeling estimates quantum state transduction fidelity exceeding $99%$ at a MHz-scale bandwidth, validating a critical requirement for fault-tolerant quantum systems.
- Architecture: A hybrid system employing an acoustic bus (phononic cavity/waveguide) couples the microwave domain (SC Qubit) via piezoelectric transduction and the optical/spin domain ($\text{SiV}^-$ in diamond) via strong strain-spin coupling.
- Scalability & Memory: The architecture provides long-lived quantum memory capacity via coupling the $\text{SiV}^-$ electron spin to neighboring $\text{C}^{13}$ nuclear spins, potentially offering thousands of memory qubits.
- Key Material Requirement: High-purity, low-loss, custom-dimensioned Single Crystal Diamond (SCD) is essential for hosting the $\text{SiV}^-$ centers and supporting the high-Q mechanical and optical cavities.
- Cavity Design: Two high-Q mechanical cavities were modeled: a heterogeneous silicon/thin diamond (100 nm) structure (2.0 GHz) and an all-diamond optomechanical structure (17.2 GHz).
- Engineering Challenge: Requires the demonstration of strong coupling of a single defect center spin to a high-quality mechanical cavity, demanding ultra-precise diamond fabrication and surface quality.
Technical Specifications
Section titled âTechnical SpecificationsâThe following key operational and material parameters were extracted from the theoretical modeling and analysis:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Target State Transfer Fidelity ($\mathcal{F}$) | > 99 | % | Required for efficient transduction |
| Transduction Bandwidth | MHz-scale | Hz | Operational speed requirement |
| Operating Temperature | $\sim$ mK | K | Required for non-thermal occupation of modes |
| Target Mechanical Quality Factor ($Q_p$) | $\sim 10^7$ | unitless | Required to limit phonon decay rate ($\gamma_p \le 10^{-7}$ GHz) |
| SCD Layer Thickness (Heterogeneous Design) | 100 | nm (0.1 ”m) | Thin diamond layer integrated onto silicon |
| SC Qubit Decay Rate ($\gamma_{sc}/2\pi$) | $\le 10^{-5}$ | GHz (10 kHz) | Conservative requirement for microsecond coherence |
| Electron Spin Decoherence Rate ($\gamma_e/2\pi$) | $\le 10^{-5}$ | GHz (10 kHz) | Max limit for achieving > 99% fidelity |
| All-Diamond Cavity Resonant Frequency ($\omega_p/2\pi$) | 17.2 | GHz | High-frequency mechanical mode analyzed |
| Maximum Bare Phonon-Spin Coupling ($g_{orb}/2\pi$) | 24 | MHz | Achieved in all-diamond optomechanical cavity (Fig. 3) |
| Optical Wavelength ($\lambda_{opt}$) | 732 | nm | SiV$^-$ optical addressing requirement |
| All-Diamond Optical Quality Factor ($Q_{opt}$) | $10^6$ | unitless | Calculated value for high efficiency optical addressing |
Key Methodologies
Section titled âKey MethodologiesâThe experimental feasibility hinges on combining precise material engineering with carefully controlled physical processes:
- High-Purity Diamond Synthesis: Use of Single Crystal Diamond (SCD) grown via MPCVD to minimize intrinsic defects and achieve sufficiently long coherence times ($T_2$) for the $\text{SiV}^-$ electron and nuclear spins.
- Cavity Fabrication (Silicon/Diamond): Creation of phononic crystal lattices and waveguides in silicon or all-diamond structures, designed to concentrate elastic energy density in a thin constriction where the $\text{SiV}^-$ centers reside.
- Strain Concentration: Engineering geometric distortions and thin diamond layers (as low as 100 nm) to achieve zero-point strain fluctuations on the order of $10^{-9}$ to $10^{-8}$ to facilitate strong spin-strain coupling ($g_{orb}$).
- Cryogenic Operation: Maintaining the system at millikelvin ($\sim$ mK) temperatures to ensure the superconducting qubit performs optimally and to avoid thermal occupation of mechanical modes.
- Coupling Modulation: Implementation of rapidly tunable couplings ($g_{sc-p}(t)$ and $g_{p-e}(t)$) via external magnetic fields, piezoelectric transducers, or optical/microwave drives.
- Pulsed State Transfer: Application of time-symmetric âpitch-and-catchâ pulse sequences to execute rapid, coherent Jaynes-Cummings SWAP gates, moving the quantum state sequentially from the SC qubit to the phonon mode and finally to the electron spin ($\text{SiV}^-$).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is an essential, high-precision supplier for the realization and scaling of this hybrid quantum transduction architecture. Our core expertise in MPCVD diamond growth, custom fabrication, and metalization directly addresses the key material challenges identified in this research.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research, high-quality CVD diamond wafers are required.
- Optical Grade Single Crystal Diamond (SCD): Required for the lowest possible background nitrogen concentration and highest material purity, which is critical for achieving the long spin coherence times ($T_2$ processes $\le 10 \text{ kHz}$) necessary for the $\text{SiV}^-$ centers and the $\text{C}^{13}$ nuclear-spin quantum memory.
- Application: SCD substrates are the host for $\text{SiV}^-$ creation, nanostructure etching (phononic/optical cavities), and subsequent integration.
- Custom Thickness SCD: The research specifically utilizes thin diamond layers (100 nm or 0.1 ”m) for heterogeneous integration and the concentration of elastic energy.
- 6CCVD Capability: We supply SCD films with thickness control down to 0.1 ”m on custom substrates, meeting the precise thickness requirements for strain-concentrating nanomechanical structures.
Customization Potential
Section titled âCustomization PotentialâThe complex architecture, which includes phononic crystal waveguides, cavities, and electrical interfaces, necessitates advanced customization capabilities.
| Requirement (Paper) | 6CCVD Customization Potential | Specification Guarantee |
|---|---|---|
| Thin Film/Membranes | Custom thickness SCD wafers (ready for etching into cavities) | Thickness control down to 0.1 ”m (SCD/PCD) |
| Ultra-Smooth Surfaces | Polishing required for high mechanical/optical Q-factors | SCD Polishing: Ra < 1 nm (Atomic flatness) |
| Complex Geometries | Custom cutting and shaping for integrated devices (Fig. 2, Fig. 3) | Laser micro-machining and custom dimensions (up to 125mm PCD) |
| Electrical Interfaces | Metalization for piezoelectric transducers and electrical contacts | Internal Metalization capabilities: Ti, Pt, Au, Pd, W, Cu |
| Substrate Size | Need for scalable, inch-sized platforms for QPU/QM integration | Wafers supplied up to 125mm diameter (PCD/BDD) |
Engineering Support
Section titled âEngineering SupportâThe successful fabrication of the high-Q phononic cavities and the integration of the $\text{SiV}^-$ centers within the zero-point strain field is an advanced technical hurdle. 6CCVDâs in-house team of PhD material scientists can assist with:
- Material Selection: Determining the optimal SCD grade (purity, isotopic composition) to maximize $\text{SiV}^-$ and $\text{C}^{13}$ spin coherence times ($T_2$).
- Interface Optimization: Consulting on the handling and surface preparation of thin SCD membranes required for high-fidelity heterogeneous integration onto silicon platforms.
- Fabrication Workflow: Assisting engineering teams in optimizing pre- and post-processing steps (polishing, cleaning) to preserve the ultra-low $\text{Ra}$ values critical for achieving high mechanical $Q$ in the fabricated cavities.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We provide global shipping (DDU default, DDP available) for expedited delivery of critical quantum-grade diamond substrates.
View Original Abstract
We introduce a method for high-fidelity quantum state transduction between a superconducting microwave qubit and the ground state spin system of a solid-state artificial atom, mediated via an acoustic bus connected by piezoelectric transducers. Applied to present-day experimental parameters for superconducting circuit qubits and diamond silicon vacancy centers in an optimized phononic cavity, we estimate quantum state transduction with fidelity exceeding 99% at a MHz-scale bandwidth. By combining the complementary strengths of superconducting circuit quantum computing and artificial atoms, the hybrid architecture provides high-fidelity qubit gates with long-lived quantum memory, high-fidelity measurement, large qubit number, reconfigurable qubit connectivity, and high-fidelity state and gate teleportation through optical quantum networks.