Scalable quantum information transfer between nitrogen-vacancy-center ensembles

At a Glance

Metadata	Details
Publication Date	2015-02-14
Journal	Annals of Physics
Authors	feng-yang Zhang, Chui-Ping Yang, He-Shan Song, feng-yang Zhang, Chui-Ping Yang
Institutions	Dalian University of Technology, Hangzhou Normal University
Citations	6
Analysis	Full AI Review Included

Technical Documentation and Analysis: Scalable QIT using NVCE in Diamond

This document analyzes the technical requirements and achievements of the research paper “Scalable quantum information transfer between nitrogen-vacancy-center ensembles” and maps them directly to 6CCVD’s diamond material and fabrication capabilities, offering tailored solutions for advancing hybrid quantum computing.

Executive Summary

This paper validates a critical architecture for scalable Quantum Information Transfer (QIT) using Nitrogen-Vacancy Center Ensembles (NVCEs) within diamond, a core application for 6CCVD materials.

Core Achievement: Proposal and theoretical validation of a hybrid QIT architecture linking two spatially-separated NVCEs via coupled flux qubits and an LC circuit data bus.
Material Role: Diamond hosting NVCEs serves as a long-lived quantum memory unit, leveraging its long coherence times ($T_{2}$ potentially approaching 1 second).
Performance Metrics: High-fidelity QIT (Fidelity F > 0.9) is achievable in both resonant and large detuning regimes.
Feasibility Confirmed: The system feasibility is verified using current experimental parameters, demonstrating a fast QIT time of $\sim 14$ ns, which is orders of magnitude shorter than the reported coherence times of the system components.
Scalability: The architecture is inherently scalable, proposing extension to multiple flux qubits and NVCEs using a single LC circuit (Fig. 8), crucial for large-scale quantum information processing (QIP).
Material Requirement: Replicating this research requires ultra-high purity Single Crystal Diamond (SCD) suitable for precise NV center creation via ion implantation and subsequent bonding to superconducting chips.

Technical Specifications

The following table summarizes the key physical and performance parameters discussed in the research paper, demonstrating the highly demanding environment of hybrid quantum circuits.

Parameter	Value	Unit	Context
NVC Zero-Field Splitting (D)	2.88	GHz	Electronic ground state characteristic
Electron Spin $T_1$	6	ms	Relaxation time (Ref. [13])
Diamond $T_2$ (Dephasing)	2	ms	Reported for isotopic purity sample (Ref. [14])
NVC $T_2$ (Recent Improvement)	Up to 1	second	Enhanced coherence time achieved (Ref. [16], [43])
Flux Qubit Size	$\sim 1$	µm	Linear dimension requirement for integration
Effective Coupling ($J$)	$\sim 70$	MHz	Demonstrated coupling between Flux Qubit and NVCE (Ref. [26])
Required QIT Time ($t$)	$\sim 14$	ns	Calculated required transfer time ($t \sim 1/J$)
Flux Qubit Coherence ($T_{2}$)	$\sim 20$	µs	Typical coherence time of superconducting flux qubits (Ref. [42])
Decoherence Rate (Modeled)	$0.001 J$	-	Simulated dissipation rates ($\kappa, \gamma_{qj}, \gamma_{Nj}$) used for robust QIT modeling (Fig. 7)

Key Methodologies

The proposed QIT architecture is based on specific hybrid material integration and resonant engineering techniques:

NVCE Creation: Nitrogen-Vacancy Center Ensembles are created within a diamond crystal, typically through ion implantation (N or C) followed by high-temperature annealing.
Hybrid Integration: The diamond crystal is bonded on top of a superconducting flux qubit chip, ensuring the NVCE layer faces the chip surface to maximize magnetic coupling.
Circuit Architecture: The system employs two flux qubits magnetically coupled to two spatially-separated NVCEs.
Data Bus Function: A common LC circuit acts as a data bus, inducing the necessary interaction and facilitating coupling between the spatially separated flux qubits.
Coupling Regimes Investigated: QIT performance is analyzed for two key regimes:
- Resonant Interaction: LC circuit frequency ($\omega$) matches the NVCE transition frequency ($\Omega_j$).
- Large Detuning: Large detuning ($\delta_j \gg g_j$) between the LC circuit and the flux qubits, leading to adiabatic elimination of the LC circuit and reduced population loss.

6CCVD Solutions & Capabilities

This research highlights the critical need for high-specification diamond substrates for scalable quantum hardware. 6CCVD is uniquely positioned to supply the materials required to replicate and scale this QIT architecture.

Applicable Materials for Hybrid Quantum Systems

To achieve the long coherence times and robust integration demonstrated in this work, high-quality, ultra-pure diamond is essential:

Optical Grade Single Crystal Diamond (SCD): This is the ideal foundational material.
- Required for minimal native nitrogen and vacancy defects, ensuring maximum NVCE coherence time ($T_{2} \to 1$ second goals).
- 6CCVD provides High Purity SCD up to 500 µm thickness, allowing precise control over the implantation depth and minimizing substrate-induced strain.
Custom Boron-Doped Diamond (BDD) / Polycrystalline Diamond (PCD):
- While SCD is preferred for the NVCE layer, BDD layers can be integrated into the diamond structure for highly conductive contacts or gate electrodes necessary for complex quantum control (e.g., $p-n$ junctions or gate voltage modulation).
- For testing or large-area prototypes, 6CCVD can supply PCD wafers up to 125mm diameter, offering cost-effective solutions for large-scale fabrication studies.

Customization Potential for QIT Device Replication

Successful device integration relies on highly controlled physical interfaces and customized fabrication features, all available through 6CCVD’s internal capabilities:

Custom Capability	Paper Requirement Alignment	6CCVD Solution Offering
Precision Polishing	Required for low-loss, high-fidelity bonding between the diamond and the superconducting chip surface.	SCD Polishing: Achieve surface roughness $R_a \lt 1$ nm. Essential for minimizing loss at the diamond/qubit interface.
Custom Dimensions	Scalability shown in Fig. 8 necessitates larger wafers than typical lab samples. Flux qubit size is $\sim 1 \mu\text{m}$ order.	Plates and wafers up to 125 mm available (PCD). SCD available up to 500 µm thickness and custom shapes/sizes via laser cutting.
Integrated Metalization	Superconducting flux qubits and LC circuits require precise metal contacts and interconnects.	Internal Metalization: In-house deposition of thin films including Ti, Pt, Au, Cu, and Pd. This allows for the integration of customized contact pads or coupling elements directly onto the diamond surface, simplifying device fabrication.
Substrate Thickness	SCD Substrates up to 10 mm available for robust handling and specialized packaging requirements in complex QIP systems.

Engineering Support

6CCVD’s in-house team of PhD material scientists and engineers understands the strict demands of hybrid quantum architectures. We provide dedicated support for:

Material Selection: Guiding customers in selecting the optimal SCD grade, orientation, and nitrogen content necessary to maximize NVCE yield and coherence properties during the ion implantation and annealing process.
Interface Engineering: Consulting on the optimal surface preparation and metalization schemes required for reliable, low-strain bonding to superconducting qubit chips.
Project Scaling: Assisting with material choices and custom dimensions for Scalable Quantum Information Transfer projects, ensuring material supply meets research demands from R&D to pilot production.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global DDP shipping options available.

Tech Support

Original Source

DOI: https://doi.org/10.1016/j.aop.2015.02.004