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	The University of Texas at Dallas, University of Washington
Citations	39
Analysis	Full AI Review Included

Executive Summary

This research computationally discovers and characterizes a promising family of spin-defect qubits (M_X family) realized in two-dimensional (2D) Transition Metal Dichalcogenides (TMDs), specifically optimized for quantum network applications.

Telecom Operation: The defects, such as W_Se in MoSe₂, exhibit Zero-Phonon Line (ZPL) optical transitions in the highly desirable telecom band (0.74-0.94 eV or 1260-1675 nm), enabling long-distance quantum communication via standard optical fibers.
High Zero-Field Splitting (ZFS): The defects possess a large spin-triplet ground state with ZFS values typically ranging from 10 to 20 GHz, significantly higher than the NV center in diamond, facilitating robust microwave control and high-temperature resonant spin readout.
Fast Radiative Decay: Calculated radiative lifetimes (T_R) are in the microsecond range (e.g., 4.2 µs for W_Se in MoSe₂), which is 100 to 1000 times faster than the NV center in diamond, supporting efficient spin initialization and readout.
2D Integration Advantage: The 2D host material allows for seamless monolithic integration with semiconductor electronics, heterostructure engineering, and precise defect placement (e.g., via STM lithography).
Strain Tunability: The ZPL energy and radiative lifetime can be finely tuned by applying mechanical strain (uniaxial or biaxial), offering a method to minimize transmission loss and create highly sensitive quantum strain sensors.
Low Nuclear Spin Noise: TMD hosts offer reduced sensitivity to nuclear spin environments and the feasibility of isotopic purification, promising long spin coherence times (T₂).

Technical Specifications

The following data was derived from hybrid Density Functional Theory (DFT) calculations, primarily focusing on the W_Se defect in monolayer MoSe₂.

Parameter	Value	Unit	Context
Defect Family	M_X	N/A	Transition metal substituted at chalcogen site
Primary Host Material	MoSe₂	N/A	Monolayer Transition Metal Dichalcogenide
Primary Defect	W_Se	N/A	Tungsten substituted at Selenium site
Zero-Phonon Line (ZPL) Energy	0.74	eV	W_Se in MoSe₂ (SOC corrected)
ZPL Wavelength (W_Se in MoSe₂)	~1675	nm	Falls within the telecom band
ZPL Energy (W_S in MoS₂)	0.94	eV	W_S in MoS₂ (SOC corrected)
Zero-Field Splitting (D) Range	10-20	GHz	General range for M_X defect family
ZFS (W_Se in MoSe₂)	7.23	GHz	Calculated D value
Radiative Lifetime (T_R)	4.2	µs	W_Se in MoSe₂
Radiative Lifetime (T_R)	20.5	µs	W_S in MoS₂
Intersystem Crossing (ISC) Time	0.031	µs	T_ISC (W_Se in MoSe₂), faster than T_R
Strain Tuning Capability (ΔE)	Hundreds	meV	Modulation of energy gap (a₁ to e_x,y) under strain
Host Point Group Symmetry	C_3v	N/A	Symmetry of the defect environment
Telecom Band Range	1260-1675	nm	Low-loss optical fiber transmission window

Key Methodologies

The discovery and characterization of the M_X defect family were achieved through systematic first-principles computational methods, primarily based on Density Functional Theory (DFT).

Initial Screening: DFT calculations using the Perdew-Burke-Ernzerhof (PBE) functional were performed to identify defects meeting two criteria: (i) spin-triplet ground state, and (ii) spin-conserving intradefect optical transition without ionization.
Hybrid DFT Calculations: Detailed electronic structures were computed using the Vienna Ab initio Simulation Package (VASP) employing the Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional to accurately model bandgaps and defect energy levels.
Supercell Setup: Monolayer TMDs (MoS₂, MoSe₂, etc.) were modeled using 6 x 6 x 1 primitive supercells, including a 15-Angstrom vacuum region to simulate the 2D environment.
Defect Formation Energy: Defect formation energies were calculated using the COFFEE (Corrections For Formation Energy and Eigenvalues) code, which applies the FNV (Freysoldt-Neugebauer-Van de Walle) charge correction scheme to account for electrostatic interactions in charged supercells.
Magnetic Properties Calculation: VASP subroutines were utilized to compute the magnetic properties, including the Zero-Field Splitting (ZFS) tensors and the hyperfine tensors (A⁽ⁿ⁾).
Optical and Vibrational Properties: Configuration coordinate diagrams were generated using constrained-occupation DFT to model the Zero-Phonon Line (ZPL) emission and estimate the Huang-Rhys factor (S).
Intersystem Crossing (ISC) Rate: The ISC rate was calculated using Fermi’s golden rule, requiring the computation of Spin-Orbit Coupling (SOC) strength via the ORCA code (using time-dependent DFT and cluster models) and phonon wavefunction overlap.
Strain Engineering Simulation: Uniaxial and biaxial strains (up to ±3%) were applied computationally to the host materials to determine the resulting modulation of radiative lifetime (T_R) and ZPL energy (δE).

Commercial Applications

The unique combination of telecom operation, high ZFS, and 2D integration capability positions the M_X defect family for several advanced engineering and quantum technology applications.

Quantum Communication and Networks:
- Long-Distance QKD: Direct operation in the 1260-1675 nm telecom band allows for seamless integration with existing low-loss optical fiber infrastructure, enabling the realization of long-distance quantum entanglement networks.
- Quantum Repeaters: The defects serve as promising solid-state quantum memory nodes for storing and transmitting quantum information.
Integrated Quantum Devices:
- Monolithic Hybrid Devices: The 2D nature of the host materials facilitates integration with conventional 3D semiconductor electronic devices, enabling the creation of scalable, monolithically integrated hybrid classical-quantum systems.
- Photonic Integration: Ease of integration with on-chip photonic platforms (waveguides, cavities) allows for enhanced photon collection efficiency via the Purcell effect, compensating for moderate oscillator strengths.
Quantum Sensing and Metrology:
- Quantum Strain Sensors: The drastic and sensitive shift of defect energy levels under small uniaxial strain makes these defects highly susceptible quantum strain sensors.
- High-Temperature Sensing: The large ZFS (10-20 GHz) enables resonant spin readout and control at higher temperatures compared to defects with smaller ZFS.
Advanced Manufacturing and Lithography:
- Precision Defect Placement: The ability to place defects precisely within a 2D layer (versus being buried in 3D bulk) using techniques like Scanning Tunneling Microscope (STM) or focused electron beam lithography is critical for manufacturing scalable quantum registers.

Tech Support

Original Source

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