All-optical coherent population trapping with defect spin ensembles in silicon carbide

At a Glance

Metadata	Details
Publication Date	2015-06-05
Journal	Scientific Reports
Authors	Olger Zwier, Danny O’Shea, A. R. Onur, C. H. van der Wal
Citations	33
Analysis	Full AI Review Included

Technical Documentation & Analysis: All-Optical Coherent Population Trapping in SiC

Executive Summary

This paper demonstrates successful all-optical coherent control of defect spin ensembles in Silicon Carbide (SiC), a crucial step toward solid-state quantum technology. While the research validates SiC divacancies ($V_{SiC}$) as promising systems, the findings reinforce the competitive advantages of our specialized CVD Diamond materials for quantum applications requiring robust coherence and integration.

Core Achievement: Direct all-optical addressing and demonstration of Coherent Population Trapping (CPT)—a key quantum control mechanism—in basal plane-oriented divacancy spin ensembles in 4H-SiC.
Quantum Significance: Confirms SiC spin ensembles (with a spin triplet structure, $S=1$) as compelling candidates for quantum-enhanced memory, communication, and field-sensing applications, comparable in principle to the Nitrogen-Vacancy ($NV^-$) center in diamond.
Spectral Advantage: The optical transition occurs at 1078.6 nm, representing a near-telecom wavelength highly desirable for integration into existing telecommunication networks and quantum device structures.
Coherence and Control: Two-laser magneto-spectroscopy was employed at 4.2 K to fully identify the spin structure and realize CPT, achieving a measured ground-state dephasing time of 42 ± 8 ns under continuous-wave (CW) laser driving.
Material Compatibility: SiC is recognized for its compatibility with well-developed semiconductor processing, but the required metalization (Ti/Au) and precise material geometries align perfectly with 6CCVD’s custom fabrication capabilities in CVD Diamond.

Technical Specifications

The following table extracts critical hard data points and material parameters essential for replicating or extending this quantum control research.

Parameter	Value	Unit	Context
Host Material Polytype	4H-SiC	N/A	High-purity, semi-insulating wafer
Wafer Thickness (Initial)	365	µm	Material dimension prior to preparation
Base Operating Temperature	4.2	K	CPT and two-laser spectroscopy
ZPL Wavelength (PL4 line)	1078.6	nm	Basal divacancy optical transition (Near-telecom)
ZPL Photon Energy	~1.15	eV	Zero-Phonon Line (ZPL)
Inhomogeneous Linewidth (PLE)	30	GHz	Observed at 16 K, attributed to strain
Ground State Dephasing Time	42 ± 8	ns	Derived from CPT dip fitting under CW driving
Excitation Laser Linewidth	< 1	MHz	CW tunable diode lasers
Applied Magnetic Field (B) Range	0 to 70	mT	Used for magneto-spectroscopy
Excited State Splitting Parameter ($D_e$)	0.95 ± 0.02	GHz	Fit from two-laser spectroscopy data
Adhesion Layer Metalization	1	nm	Titanium (Ti)
Mirror/Contact Metalization	100	nm	Gold (Au)

Key Methodologies

The following is a concise summary of the fabrication and experimental parameters used to achieve all-optical CPT in the SiC divacancy ensembles.

Sample Fabrication: High-purity, semi-insulating 4H-SiC wafers (365 µm thick) were cleaved using a diamond-tipped stylus to achieve optimized geometry for Photoluminescence Excitation (PLE) detection.
Metalization Coating: A dual-layer metal stack consisting of a 1 nm Titanium (Ti) adhesion layer and a 100 nm Gold (Au) mirror coating was evaporated onto the front and back surfaces. A hard mask ensured a window for laser coupling.
Cryogenic Environment: Experiments were conducted in a liquid-helium flow cryostat, maintaining temperature stability within 0.01 K (primarily operating at 4.2 K or 16 K).
Optical Excitation: Two continuous-wave (CW) diode lasers, stabilized to < 1 MHz linewidth, were tuned near the 1078.6 nm ZPL. Laser powers were varied between 30 µW and 3 mW. A 685 nm repumping laser was continuously applied to counter selective charge state bleaching.
Magnetic Field Control: A superconducting magnet generated magnetic fields up to 70 mT, fixed along the direction of photoluminescence collection.
Spectroscopy Technique: Two-laser spectroscopy was performed by fixing one laser centrally on the ZPL and scanning the second laser frequency (10 MHz/sec scan rate) to identify homogeneous transition frequencies and spin-related fine structures. Resolution was optimized to 2 MHz.

6CCVD Solutions & Capabilities

This research highlights the continued drive towards solid-state quantum platforms. While SiC provides certain integration benefits, the observed dephasing time (42 ns) is significantly shorter than the millisecond coherence times achieved with $NV^-$ centers hosted in high-purity CVD diamond. 6CCVD offers expert material solutions to advance similar spin-ensemble and single-qubit projects, providing superior materials and integrated fabrication services.

Applicable Materials

Research Requirement	Recommended 6CCVD Material	Technical Advantage
High Spin Coherence Time	Optical Grade Single Crystal Diamond (SCD)	SCD is the gold standard for solid-state qubits, offering ultra-low nitrogen content necessary to synthesize $NV^-$ centers with coherence times ($T_2$) orders of magnitude longer than observed SiC divacancies.
Scaling & Uniformity	High Purity Polycrystalline Diamond (PCD)	For large-area sensing or bulk applications requiring high defect density ensembles, our PCD offers wafer-scale uniformity up to 125 mm diameter.
Integrated Electrodes/Sensing	Heavy Boron-Doped Diamond (BDD)	BDD provides conductive diamond surfaces necessary for applying local electric fields (as used in electrically tunable spin systems) or creating integrated diamond electronics adjacent to the spin ensemble.

Customization Potential

The experimental success hinges on precise material preparation and external control elements, aligning perfectly with 6CCVD’s customization services.

Precision Geometry and Thickness: The SiC sample was cut from a 365 µm thick wafer. 6CCVD offers Single Crystal Diamond (SCD) Substrates up to 10 mm in thickness, and standard SCD thicknesses from 0.1 µm up to 500 µm, custom-cut to precise dimensions (e.g., millimeter-scale plates or optimized geometries for photonic integration).
Metalization Replication: The paper required a Ti/Au metal stack (1 nm Ti adhesion / 100 nm Au mirror). 6CCVD has established internal capabilities to deposit and pattern complex metalization stacks directly onto diamond surfaces, including Au, Pt, Pd, Ti, W, and Cu. We can guarantee stack quality and adhesion consistency.
Surface Preparation for Integration: The creation of integrated quantum device structures (waveguides, photonic crystals) mentioned in the paper requires ultra-smooth surfaces. 6CCVD guarantees SCD polishing down to Ra < 1 nm and large-area PCD polishing down to Ra < 5 nm, critical for low-loss optical coupling.

Engineering Support

6CCVD provides dedicated technical consultation to transition quantum research from promising bulk demonstrations to robust integrated devices. Our in-house PhD team can assist with:

Material Selection: Guiding researchers on selecting the optimal diamond polytype (SCD vs. PCD) and dopant level (e.g., Boron) to maximize spin lifetime and address specific needs for Solid-State Spin Qubits and Field-Sensing projects.
Defect Engineering: Optimizing growth parameters to control the concentration and depth of $NV^-$ or other defect centers for enhanced signal strength and device scaling.
Global Logistics: Utilizing DDU (default) or DDP shipping options to ensure reliable, timely delivery of high-value custom diamond products globally, supporting complex international research timelines.

Call to Action: For custom specifications, metalization design, or material consultation specific to spin ensemble experiments, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1038/srep10931