Spin-defect qubits in two-dimensional transition metal dichalcogenides operating at telecom wavelengths

At a Glance

Metadata	Details
Publication Date	2022-12-06
Journal	Nature Communications
Authors	Yeonghun Lee, Yaoqiao Hu, Xiuyao Lang, Dongwook Kim, Kejun Li
Institutions	University of California, Santa Cruz, The University of Texas at Dallas
Citations	39
Analysis	Full AI Review Included

Technical Documentation & Analysis: Spin-Defect Qubits in 2D TMDs

Executive Summary

This computational study identifies the $M_X$ defect family in monolayer Transition Metal Dichalcogenides (TMDs) as highly promising candidates for solid-state spin qubits, offering distinct advantages over established 3D systems like the Nitrogen-Vacancy ($NV^-$) center in diamond.

Telecom Operation: The $M_X$ defects (e.g., $W_{Se}$ in $MoSe_2$) exhibit Zero-Phonon Line (ZPL) transitions around 0.74 eV to 0.94 eV, placing them directly in the highly desirable optical fiber telecom band (1260-1675 nm).
High Zero-Field Splitting (ZFS): Calculated ZFS values (D) are in the 10-20 GHz range, significantly higher than the 2.86 GHz benchmark of the $NV^-$ center in diamond, enabling high-temperature resonant spin readout.
Favorable Optical Properties: The defects show high Debye-Waller (DW) factors (up to 0.47 for $W_S$ in $MoS_2$) and fast Inter-System Crossing (ISC) rates (0.031 µs for $W_{Se}$), supporting efficient spin initialization and readout.
Tunability and Integration: The 2D nature of the host materials allows for effective strain engineering to fine-tune ZPL energy by hundreds of meV, crucial for single-frequency operation in quantum networks.
6CCVD Context: While the research focuses on TMDs, the $NV^-$ center in Single Crystal Diamond (SCD) is used as the critical 3D benchmark. 6CCVD supplies the highest quality SCD required for replicating and extending $NV^-$ research, alongside advanced customization capabilities necessary for integrating any solid-state qubit platform.

Technical Specifications

The following table summarizes key calculated parameters for the $W_{Se}$ defect in $MoSe_2$ and the benchmark $NV^-$ center in Diamond, as presented in the research.

Parameter	Value (W_Se in MoSe₂)	Unit	Context / Comparison
Host Bandgap (E_g)	2.07 (1.72)	eV	SCD Diamond E_g is 5.47 eV. Parentheses indicate Spin-Orbit Coupling (SOC) correction.
Zero-Phonon Line (ZPL)	0.79 (0.74)	eV	Telecom band operation (0.74 eV corresponds to ~1675 nm).
Zero-Field Splitting (D)	12.43	GHz	Large ZFS, approximately 4x greater than NV^- in Diamond (2.86 GHz).
Radiative Lifetime (T_R)	4.2	µs	Slower than NV^- (0.014 µs), but 5 orders of magnitude faster than Er-based qubits.
Debye-Waller (DW) Factor	0.14	N/A	High DW factor compared to NV^- (0.05), indicating strong ZPL emission.
ISC Transition Rate (Γ_ISC)	0.031	µs	Fast ISC rate, enabling spin-selective decay pathways for readout.
Hyperfine Tensor (A_zz)	333.0	MHz	Calculated for the ¹⁸³W (I = 1/2) nucleus.
Strain Tuning Range (ZPL)	Hundreds	meV	Demonstrated tunability via uniaxial/biaxial strain (Fig. 5).

Key Methodologies

The research utilized advanced first-principles computational methods to characterize the defect family, focusing on electronic, magnetic, vibrational, and optical properties.

Density Functional Theory (DFT): Calculations were performed using the Vienna Ab initio Simulation Package (VASP).
Hybrid Functional: The Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional was used to accurately address the bandgap problem inherent in local exchange-correlation functionals.
Supercell Modeling: A 6 × 6 × 1 primitive cell supercell was used for monolayer TMDs, including a 15-Å-thick vacuum region.
Charge Correction: The Freysoldt-Neugebauer-Van de Walle (FNV) correction scheme was employed to account for spurious image charge effects in anisotropic 2D materials when calculating defect formation energy.
Spin-Orbit Coupling (SOC): SOC effects were included in calculations for heavy elements (W, Se) to determine corrected ZPL energies and assess effects on spin coherence.
ZPL and DW Factor Calculation: Configuration coordinate diagrams were generated using constrained DFT to calculate the ZPL energy, Huang-Rhys factor (S), and the resulting DW factor (DW = e^-S).
Magnetic Properties: Subroutines implemented in VASP were used to compute the Zero-Field Splitting (ZFS) tensors and hyperfine tensors.
Intersystem Crossing (ISC): The ISC rate was calculated using Fermi’s golden rule, incorporating SOC and electron-phonon interaction, and utilizing cluster models with the ORCA code for SOC strength computation.

6CCVD Solutions & Capabilities

6CCVD is the world-leading supplier of MPCVD diamond materials, providing the foundational platforms necessary for both benchmarking and advancing solid-state qubit research. While this paper focuses on 2D TMDs, the $NV^-$ center in diamond remains the critical benchmark for coherence and stability, and 6CCVD’s capabilities directly address the integration and material challenges faced by all solid-state quantum platforms.

Applicable Materials

To replicate the $NV^-$ benchmark data or to develop hybrid quantum systems integrating 2D materials with robust 3D platforms, 6CCVD recommends the following materials:

6CCVD Material	Recommended Specification	Application in Quantum Research
Optical Grade SCD	SCD, High Purity, [100] or [111] orientation, Thickness 10 µm - 500 µm, Ra < 1 nm	Ideal host for high-coherence $NV^-$ centers, serving as the established 3D benchmark for ZFS and $T_2$ times.
Thin SCD Wafers	SCD, Thickness 0.1 µm - 10 µm, Polished Ra < 1 nm	Essential for creating surface-near $NV^-$ defects, facilitating integration with photonic structures (e.g., cavities) and enabling hybrid integration with 2D TMDs.
Boron-Doped Diamond (BDD)	PCD or SCD, Heavy Doping (Conductive)	Required for advanced quantum sensing applications (magnetometry, electrometry) where conductive diamond is necessary for microwave delivery or charge state control.
Polycrystalline Diamond (PCD)	Wafers up to 125 mm diameter, Polished Ra < 5 nm	Cost-effective substrates for large-scale deposition or integration of 2D materials like TMDs and hBN.

Customization Potential

The research highlights the need for precise integration, cavity coupling (Purcell effects), and strain engineering—all areas where 6CCVD provides critical material customization:

Custom Dimensions and Thickness: 6CCVD offers SCD and PCD plates/wafers up to 125 mm in diameter and thicknesses ranging from 0.1 µm to 10 mm. This capability is vital for researchers requiring ultra-thin membranes for strain application or large substrates for high-throughput fabrication.
Advanced Metalization Services: The paper discusses the necessity of cavity integration to reduce the radiative lifetime ($T_R$) via Purcell effects. 6CCVD provides in-house metalization (Au, Pt, Pd, Ti, W, Cu) for creating on-chip microwave antennas, electrical contacts, and photonic structures directly on the diamond surface, enabling efficient spin manipulation and readout.
Ultra-Low Roughness Polishing: Achieving high-quality interfaces for 2D material deposition (like the TMDs discussed) or for coupling to optical cavities requires exceptional surface quality. 6CCVD guarantees ultra-low surface roughness (Ra < 1 nm for SCD) essential for minimizing scattering losses and maximizing coupling efficiency.

Engineering Support

6CCVD’s in-house PhD team specializes in MPCVD growth, defect engineering, and material characterization for quantum applications. We offer authoritative professional support to researchers working on:

Material Selection: Assisting in selecting the optimal diamond type (SCD vs. PCD, doping level, orientation) to maximize $NV^-$ coherence times or to serve as a robust platform for 2D material integration.
Defect Creation and Control: Consulting on methods for creating shallow $NV^-$ centers or other color centers (e.g., SiV, GeV) that are competitive with the telecom-band defects discovered in TMDs.
Hybrid System Design: Providing technical consultation on integrating diamond with other materials, including metalization stack design for microwave control and photonic coupling.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41467-022-35048-0