Realization of a multinode quantum network of remote solid-state qubits
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-04-15 |
| Journal | Science |
| Authors | Pompili M, S. L. N. Hermans, S. Baier, H. K. C. Beukers, P. C. Humphreys |
| Institutions | QuTech, Delft University of Technology |
| Citations | 564 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Multi-Node Quantum Network using NV Diamond
Section titled âTechnical Documentation & Analysis: Multi-Node Quantum Network using NV DiamondâReference Paper: Pompili et al., âRealization of a multi-node quantum network of remote solid-state qubitsâ (arXiv:2102.04471v1, 2021).
Executive Summary
Section titled âExecutive SummaryâThis research successfully demonstrates the realization of a three-node quantum network utilizing Nitrogen-Vacancy (NV) centers in diamond, establishing a critical platform for the future quantum internet.
- Core Achievement: First experimental realization of a three-node entanglement-based quantum network using solid-state qubits (NV centers in diamond).
- Key Protocols Demonstrated: Successful distribution of genuine multipartite entangled Greenberger-Horne-Zeilinger (GHZ) states (Fidelity F = 0.538(18)) and entanglement swapping (Average Fidelity F = 0.551(13)).
- Material Requirement: The network relies on high-purity, low-strain Single Crystal Diamond (SCD) to host indistinguishable NV communication qubits and controlled 13C nuclear spins for robust memory qubits.
- Scalable Architecture: Implemented a scalable, phase-stabilized architecture using a hybrid detection scheme (local heterodyne, global homodyne) and real-time feed-forward operations for heralded state delivery.
- High Fidelity Links: Achieved Bell state fidelities exceeding 0.8 on elementary links, demonstrating performance on par with the highest reported single-link experiments.
- Device Integration: Requires precision diamond processing, including on-chip metalization for DC Stark tuning and microwave (MW) pulse delivery, capabilities offered by 6CCVD.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points summarize the performance and physical parameters of the demonstrated quantum network:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Network Size | 3 | Nodes | Alice, Bob, Charlie configuration. |
| Communication Qubit Material | NV Center in Type-IIa SCD | N/A | High-purity, low-strain CVD diamond. |
| Memory Qubit Material | 13C Nuclear Spin | N/A | Located in the central node (Bob). |
| GHZ State Fidelity (Measured) | 0.538(18) | N/A | Certifies genuine multipartite entanglement (F > 0.5). |
| Entanglement Swapping Fidelity (Average) | 0.551(13) | N/A | Average fidelity across all BSM outcomes. |
| Bell State Fidelity (Highest Link) | 0.820(5) | N/A | Alice-Bob link fidelity. |
| GHZ State Delivery Rate | 1/(90) | s-1 | Heralded generation rate. |
| Entanglement Swapping Rate | 1/(40) | s-1 | Heralded rate (combining all BSM results). |
| Operating Temperature | 4 | K | Cryogenic environment for NV centers. |
| Magnetic Field (Bob Node) | 189 | mT | Used to increase 13C memory qubit robustness. |
| Intrinsic Memory Coherence (T2*) | 11.6(2) | ms | Equivalent to ~2000 entanglement attempts. |
| Optical Working Frequency | 470.455 55 | THz | Corresponds to 637.25 nm ZPL transition. |
| MW Pulse Error (Estimated) | 0.1% to 1% | N/A | Error budget for Hermite MW pulses across nodes. |
Key Methodologies
Section titled âKey MethodologiesâThe experimental success relies on precise material engineering and advanced control protocols:
- Diamond Substrate Preparation: Use of high-purity, Type-IIa CVD Single Crystal Diamond (SCD) cut along the (111) orientation, optimized for NV center performance.
- Optical Interface Fabrication: Solid Immersion Lenses (SILs) and Anti-Reflection (AR) coatings are fabricated directly onto the diamond surface to maximize photon collection efficiency (~10%).
- Qubit Resonance Tuning: DC Stark tuning is employed to bring the optical transition frequencies of all three NV centers into resonance (indistinguishability). This requires on-chip bias fields generated via metalized strip-lines.
- Hybrid Phase Stabilization: A novel scheme combining local heterodyne phase detection (using ~1% reflected excitation light off the diamond surface) and global single-photon-level homodyne detection is used to maintain phase stability across the fiber links.
- Memory Qubit Protection: The 13C nuclear spin memory qubit is operated at a high magnetic field (189 mT) to reduce dephasing errors, requiring active temperature stabilization of the permanent magnet to achieve < 1 ”T field stability.
- Real-Time Feed-Forward: An asynchronous bi-directional serial communication scheme between micro-controllers and Arbitrary Waveform Generators (AWGs) enables real-time translation of measurement outcomes into conditional quantum gates (e.g., Z-rotation compensation on the nuclear spin).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe realization of this multi-node quantum network hinges on access to highly specialized diamond materials and precision fabrication. 6CCVD is uniquely positioned to supply the necessary components to replicate, scale, and advance this research.
Applicable Materials
Section titled âApplicable MaterialsâTo achieve the high coherence and indistinguishability required for remote entanglement, researchers need diamond substrates with exceptional purity and strain control.
| Research Requirement | 6CCVD Solution & Material | Technical Advantage |
|---|---|---|
| High-Purity Qubits (NV Centers) | Optical Grade Single Crystal Diamond (SCD) | Ultra-low strain, Type-IIa purity, and controlled nitrogen concentration for optimal NV creation and long spin coherence times. |
| Robust Memory Qubits (13C) | Isotopically Controlled SCD | We offer SCD with tailored 13C concentrations, essential for engineering nuclear spin memory registers, replicating the high-field robustness demonstrated at 189 mT. |
| On-Chip MW/DC Control | Custom Metalized Diamond (SCD/PCD) | SCD or PCD substrates pre-patterned with high-quality metal films (e.g., Au, Ti/Pt/Au) for fabricating the strip-lines and electrodes necessary for DC Stark tuning and MW pulse delivery. |
Customization Potential
Section titled âCustomization PotentialâThe experimental setup requires integrating the diamond into complex optical and cryogenic systems, often demanding non-standard geometries and surface treatments.
- Custom Dimensions and Geometry: 6CCVD provides Custom SCD Plates and Wafers up to 125mm (PCD) and custom SCD dimensions up to 10mm thick. We can supply substrates tailored for specific cryostat mounts and optical integration, including precise laser cutting for complex geometries required for SIL fabrication.
- Precision Polishing: The phase stabilization scheme relies on light reflected off the diamond surface. We guarantee Ultra-Low Roughness Polishing (Ra < 1 nm for SCD) to minimize scattering losses and ensure optimal optical coupling for both excitation and single-photon paths.
- Advanced Metalization Services: We offer In-House Metalization (Au, Pt, Pd, Ti, W, Cu) to deposit multi-layer stacks with high adhesion and low resistance, critical for the on-chip DC bias fields and microwave control lines used in this architecture.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team specializes in the material science of quantum defects and can assist researchers in optimizing their diamond specifications for similar Quantum Network and Distributed Quantum Computing projects. We provide consultation on:
- Isotopic Engineering: Selecting the optimal 12C/13C ratio for maximizing T2* coherence or enabling specific nuclear spin logic gates.
- Crystal Orientation: Supplying (111) or (100) oriented diamond based on the specific NV alignment and strain requirements of the experiment.
- Surface Preparation: Ensuring the diamond surface is prepared optimally for subsequent device fabrication steps (e.g., SIL etching, metal deposition, and AR coating).
Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
A three-node quantum network Future quantum networks will provide the means to develop truly secure communication channels and will have applications in many other quantum-based technologies. Pompili et al. present a three-node remote quantum network based on solid-state spin qubits (nitrogen-vacancy centers in diamond) coupled by photons. The implementation of two quantum protocols on the network. entanglement distribution and entanglement swapping, illustrates a key platform for exploring, testing, and developing multinode quantum networks and quantum protocols. Science , this issue p. 259