Coupling a single nitrogen-vacancy center to a superconducting flux qubit in the far-off-resonance regime
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-11-30 |
| Journal | Physical Review A |
| Authors | Tom Douce, Michael Stern, N. Zagury, Patrice Bertet, P. Milman |
| Institutions | Centre National de la Recherche Scientifique, CEA Paris-Saclay |
| Citations | 17 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Hybrid NV-Flux Qubit Coupling
Section titled âTechnical Documentation & Analysis: Hybrid NV-Flux Qubit CouplingâThis document analyzes the requirements for realizing a hybrid quantum system coupling a Nitrogen-Vacancy (NV) center in diamond to a superconducting flux qubit (FQ), focusing on material specifications and 6CCVDâs capabilities to support this advanced quantum research.
Executive Summary
Section titled âExecutive SummaryâThis research proposes a robust theoretical framework for coupling highly detuned quantum systemsâa diamond NV center and a superconducting flux qubit (FQ)âfor quantum information processing.
- Core Achievement: Demonstrates effective coupling ($g/2\pi \sim 100$ kHz) between the NV spin and the FQ in the far off-resonance regime ($\Delta - \omega_S \sim 300-500$ MHz).
- Methodology: Coupling is achieved by strongly driving (dressing) the FQ with a classical microwave field, creating dressed states whose frequency can be tuned to match the detuning.
- Material Requirement: Requires ultra-high purity Single Crystal Diamond (SCD) to host the NV center, leveraging its low decoherence rates ($\Gamma_S$) for long-term quantum memory applications.
- Precision Engineering: Successful coupling relies on placing the NV center within $r \approx 15$ nm of the superconducting constriction, demanding exceptional surface quality (Ra < 1 nm) for subsequent nanofabrication.
- Quantum Protocols: Protocols are validated for spin state initialization, arbitrary single-qubit rotations, and full state tomography, achieving high fidelity (up to 0.97) even with realistic FQ decoherence times ($T_1 \sim 20$ ”s).
- 6CCVD Value Proposition: 6CCVD provides the necessary Electronic Grade SCD substrates, custom dimensions (up to 125mm), ultra-low roughness polishing, and integrated metalization services required for the precise fabrication of the hybrid device.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the analysis, highlighting the critical physical and operational parameters of the proposed hybrid system.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| NV Center Zero-Field Splitting ($D/2\pi$) | 2.88 | GHz | Electronic ground state splitting. |
| Electron Gyromagnetic Ratio ($ | \gamma_e | /2\pi$) | 28 |
| Required Spin-Qubit Distance ($r$) | 15 | nm | Critical proximity for efficient coupling. |
| Flux Qubit Persistent Current ($I_p$) | 500 | nA | Used to calculate coupling strength. |
| Target Coupling Constant ($g/2\pi$) | 100 | kHz | Achieved at $r=15$ nm. |
| Resonance Detuning ($\Delta - \omega_S$)/$2\pi$ | 300 - 500 | MHz | Typical detuning overcome by dressing. |
| FQ Energy Relaxation Time ($T_{1}$) | 10 - 20 | ”s | Realistic experimental range for FQ. |
| FQ Dephasing Time ($T_{2}$) | 10 - 15 | ”s | Realistic experimental range for FQ. |
| Initialization Fidelity (5 Iterations) | 0.97 | N/A | Achieved with $T_{1}=20$ ”s, $T_{2}=15$ ”s. |
Key Methodologies
Section titled âKey MethodologiesâThe theoretical proposal relies on precise material preparation and the application of external fields to achieve effective coupling between the highly detuned systems.
- NV Center Preparation: Utilize a negatively-charged NV center (Spin S=1) embedded in high-purity diamond.
- Zeeman Splitting: Apply an external magnetic field ($B_{ext}$) along the NV axis to lift the degeneracy of the $m_S = \pm 1$ levels, creating a two-level system.
- Flux Qubit (FQ) Tuning: Tune the magnetic flux threading the FQ loop ($\Phi$) precisely to half a flux quantum ($\Phi = \Phi_{0}/2$) to operate at the optimal point, maximizing the FQ coherence time.
- Physical Proximity: Position the NV center extremely close ($r \approx 15$ nm) to the FQ constriction to maximize the magnetic dipole coupling ($g$).
- Classical Microwave Dressing: Subject the FQ to an intense classical microwave magnetic field (frequency $\omega = \Delta$) normal to the persistent currents. This strong driving creates âdressed statesâ in the FQ.
- Effective Coupling: The dressed states enable an effective, tunable coupling between the NV spin and the FQ, overcoming the large natural frequency detuning ($\Delta - \omega_S$).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe successful realization of this hybrid quantum device hinges on the quality and precision of the diamond substrate and subsequent nanofabrication. 6CCVD is uniquely positioned to supply the foundational materials and engineering services required for this research.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate or extend this research, the highest quality diamond is mandatory to ensure the intrinsic properties of the NV center (long coherence times) are preserved.
- Electronic Grade Single Crystal Diamond (SCD): Required for hosting isolated NV centers with minimal background spin noise. 6CCVD offers low-nitrogen concentration SCD, critical for maximizing $T_{2}$ and $T_{2}^{*}$ coherence times necessary for quantum memory applications.
- Custom Thickness: We provide SCD plates in the required thickness range (0.1 ”m to 500 ”m) for optimal integration into superconducting circuit architectures.
Customization Potential
Section titled âCustomization PotentialâThe integration of the NV center and the FQ requires complex, multi-layer fabrication steps, which 6CCVD supports through advanced processing capabilities.
| Requirement from Paper | 6CCVD Capability | Technical Specification |
|---|---|---|
| Ultra-Close Proximity (15 nm) | Precision Polishing: Essential for minimizing the gap between the NV layer and the deposited superconducting circuit. | Surface roughness (Ra) < 1 nm (SCD). |
| Superconducting Circuit Integration | Custom Metalization: We offer in-house deposition of metals commonly used in superconducting circuits (e.g., Ti adhesion layers, Au/Pt contacts, or W/Cu for specific applications). | Au, Pt, Pd, Ti, W, Cu (Internal capability). |
| Scalability and Device Size | Custom Dimensions: We can provide large-area substrates for scaling up the fabrication process and integrating multiple qubits. | Plates/wafers up to 125 mm (PCD) and large-area SCD. |
| Precise Device Definition | Laser Cutting/Machining: Custom shaping and dicing of diamond substrates to fit specific cryostat or chip carrier requirements. | Custom dimensions and geometries available. |
Engineering Support
Section titled âEngineering SupportâThe challenges inherent in hybrid quantum systemsâespecially those requiring nanoscale proximity and integration of disparate materials (superconductors and semiconductors)âdemand expert consultation.
- 6CCVDâs in-house PhD team specializes in MPCVD growth and material optimization for quantum applications. We can assist researchers in selecting the optimal SCD grade and orientation to maximize NV center yield and coherence for similar Hybrid Quantum Computing and Quantum Memory projects.
- We offer consultation on surface preparation techniques necessary to ensure compatibility between the diamond substrate and subsequent low-temperature superconducting thin-film deposition processes.
Call to Action
Section titled âCall to ActionâTo achieve the stringent material specifications required for nanoscale NV-qubit coupling, rely on 6CCVDâs expertise in high-purity diamond substrates and custom processing.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
We present a theoretical proposal to couple a single Nitrogen-Vacancy (NV)\ncenter to a superconducting flux qubit (FQ) in the regime where both systems\nare off resonance. The coupling between both quantum devices is achieved\nthrough the strong driving of the flux qubit by a classical microwave field\nthat creates dressed states with an experimentally controlled characteristic\nfrequency. We discuss several applications such as controlling the NV centerâs\nstate by manipulation of the flux qubit, performing the NV center full\ntomography and using the NV center as a quantum memory. The effect of\ndecoherence and its consequences to the proposed applications are also\nanalyzed. Our results provide a theoretical framework describing a promising\nhybrid system for quantum information processing, which combines the advantages\nof fast manipulation and long coherence times.\n