Hybrid Quantum Device Based onNVCenters in Diamond Nanomechanical Resonators Plus Superconducting Waveguide Cavities
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-10-08 |
| Journal | Physical Review Applied |
| Authors | Peng-Bo Li, Yong Chun Liu, S.Y. Gao, Ze-Liang Xiang, Peter Rabl |
| Institutions | TU Wien, Collaborative Innovation Center of Quantum Matter |
| Citations | 88 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Hybrid Quantum Devices using MPCVD Diamond
Section titled âTechnical Documentation & Analysis: Hybrid Quantum Devices using MPCVD DiamondâExecutive Summary
Section titled âExecutive SummaryâThis research demonstrates a highly efficient hybrid quantum architecture integrating Nitrogen-Vacancy (NV) centers in single-crystal diamond (SCD) nanomechanical resonators with superconducting Coplanar Waveguide (CPW) cavities.
- Core Achievement: Realization of coherent information transfer between a single NV spin qubit and a microwave photon via mechanically dark polaritons.
- Strong Coupling: Achieved strong coupling regimes for both photon-motion ($g/2\pi \sim 16$ kHz) and spin-motion ($\lambda/2\pi \sim 16$ kHz), exceeding direct magnetic coupling by three orders of magnitude.
- Mechanism: Coupling is mediated by dielectric interaction (via an AC electric field) and a strong magnetic field gradient ($\sim 10^7$ T/m).
- Material Requirement: Requires ultra-high purity, single-crystal diamond (SCD) to host stable NV centers and achieve exceptional mechanical quality factors ($Q > 10^5$).
- Thermal Management: Successfully modeled ground state cooling of the mechanical mode to $n_f \sim 0.3$ using cavity-assisted sideband cooling in a dilution refrigerator environment ($T \sim 20$ mK).
- Scalability: The proposed design is scalable and compatible with lithographic processes for large arrays of diamond microbeams.
Technical Specifications
Section titled âTechnical SpecificationsâThe following critical parameters were identified for achieving the strong coupling regime and quantum state transfer:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Material | Single Crystal (SCD) | N/A | Required for NV center coherence and high $Q$ |
| Optimal Beam Length ($l$) | 80 | ”m | Doubly clamped microbeam resonator |
| Beam Radius ($r$) | 50 - 100 | nm | Cross-sectional radius of the diamond beam |
| Mechanical Quality Factor ($Q$) | > 105 | N/A | Demonstrated in recent SCD cantilevers |
| Fundamental Frequency ($\omega_m/2\pi$) | 320 | kHz | Lowest vibrational mode |
| Final Phonon Number ($n_f$) | 0.3 | N/A | Achieved via sideband cooling |
| CPW Cavity Frequency ($\omega_c/2\pi$) | 2 - 6 | GHz | Typical range for $L \sim 1$ cm stripline |
| Photon-Motion Coupling ($g/2\pi$) | 16 | kHz | Achieved via dielectric interaction |
| Spin-Motion Coupling ($\lambda/2\pi$) | 16 | kHz | Achieved via $10^7$ T/m magnetic gradient |
| AC Electric Field Amplitude ($E_p$) | 10 | V/”m | Applied via external electrodes |
| Magnetic Field Gradient ($\partial B/\partial x$) | 107 | T/m | Generated by a micromagnet (e.g., Co nanobar) |
Key Methodologies
Section titled âKey MethodologiesâThe experimental design relies on precise material engineering and advanced cryogenic techniques:
- Diamond Nanofabrication: Fabrication of microscale, doubly clamped diamond beams (nanoresonators) from high-quality Single Crystal Diamond (SCD) using techniques compatible with achieving ultra-low dimensions (e.g., $r \sim 100$ nm).
- NV Center Integration: Embedding a single, well-controlled NV center spin within the diamond beam, requiring precise implantation or growth control in ultrapure SCD.
- CPW Integration: Positioning the diamond nanoresonator in the near field (approximately 1 ”m distance) of a superconducting CPW cavity fabricated on a dielectric substrate.
- Dielectric Coupling Actuation: Applying a strong AC electric field ($E_p$) via external electrodes to induce a macroscopic electric dipole moment in the diamond, enabling strong photon-phonon coupling.
- Spin-Motion Coupling: Utilizing a micromagnet (e.g., Co nanobar) to generate a large magnetic field gradient ($\sim 10^7$ T/m) along the beamâs axis to mediate strong spin-motion interaction.
- Quantum Cooling: Operating the system in a dilution refrigerator ($T \sim 20$ mK) and employing cavity-assisted sideband cooling in the resolved sideband regime ($\omega_m \gg \kappa$) to reach the mechanical quantum ground state.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the foundational diamond materials and advanced processing required to replicate and extend this cutting-edge hybrid quantum research.
Applicable Materials
Section titled âApplicable MaterialsâTo achieve the exceptional mechanical quality factors ($Q > 10^5$) and long spin coherence times ($T_2$) necessary for this strong coupling regime, the following 6CCVD materials are essential:
| Material Specification | 6CCVD Offering | Relevance to Research |
|---|---|---|
| Single Crystal Diamond (SCD) | Optical Grade SCD (Ultra-High Purity) | Essential for minimizing defects and maximizing NV center spin coherence ($T_2$ up to milliseconds), critical for qubit performance. |
| Thin Film SCD | SCD Layers (0.1 ”m - 500 ”m) | Provides the thin, high-quality starting material required for fabricating the microscale nanoresonators (beams with $r \sim 100$ nm). |
| Custom Doping | Controlled NV Precursors | While the paper focuses on single NV centers, 6CCVD can provide materials optimized for controlled NV creation via implantation or in-situ doping. |
Customization Potential
Section titled âCustomization PotentialâThe fabrication of this hybrid device requires precise dimensional control and integration with superconducting circuitry. 6CCVD offers the following capabilities to meet these specific engineering demands:
- Custom Dimensions: We supply SCD plates and wafers up to 125 mm in size, providing ample material for fabricating large arrays of microbeams, supporting the scalability mentioned in the conclusion.
- Precision Thickness Control: We provide SCD substrates and thin films with thickness control from 0.1 ”m up to 500 ”m, enabling researchers to optimize the Euler-Bernoulli parameters for specific resonance frequencies ($\omega_m/2\pi \sim 320$ kHz).
- Advanced Polishing: Our internal polishing capabilities achieve surface roughness Ra < 1 nm on SCD. Minimizing surface defects is crucial for maintaining high mechanical $Q$ factors and reducing surface-related decoherence.
- Custom Metalization Services: The CPW cavity and external electrodes require precise metal deposition. 6CCVD offers in-house metalization using materials including Ti, Pt, Au, Pd, W, and Cu, allowing for direct integration of contact pads or CPW components onto the diamond substrate or beam structure.
- Laser Cutting and Shaping: We offer precision laser cutting services to define complex geometries and micro-structures, assisting in the initial definition of the doubly clamped diamond beams.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD engineering team specializes in diamond material science for quantum applications. We can assist researchers in:
- Material Selection: Optimizing the SCD grade and thickness required to balance mechanical stability, NV center performance, and integration compatibility with superconducting CPW circuits.
- Interface Optimization: Consulting on metalization recipes and surface preparation techniques necessary for robust, low-loss interfaces between the diamond resonator and the superconducting cavity.
- Replication and Extension: Providing expert guidance for scaling up similar Spin-Electromechanical Hybrid Quantum projects, leveraging our experience in high-purity MPCVD growth.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
We propose and analyze a hybrid device by integrating a microscale diamond beam with a single built-in nitrogen-vacancy (NV) center spin to a superconducting coplanar waveguide (CPW) cavity. We find that under an ac electric field the quantized motion of the diamond beam can strongly couple to the single cavity photons via dielectric interaction. Together with the strong spin-motion interaction via a large magnetic field gradient, it provides a hybrid quantum device where the dia- mond resonator can strongly couple both to the single microwave cavity photons and to the single NV center spin. This enables coherent information transfer and effective coupling between the NV spin and the CPW cavity via mechanically dark polaritons. This hybrid spin-electromechanical de- vice, with tunable couplings by external fields, offers a realistic platform for implementing quantum information with single NV spins, diamond mechanical resonators, and single microwave photons.