Laser Pulses for Studying Photoactive Spin Centers with EPR

At a Glance

Metadata	Details
Publication Date	2025-03-28
Journal	Micromachines
Authors	G. V. Mamin, Ekaterina Dmitrieva, Fadis F. Murzakhanov, Margarita A. Sadovnikova, S. S. Nagalyuk
Institutions	Ioffe Institute, Kazan Federal University
Citations	1
Analysis	Full AI Review Included

Technical Documentation & Analysis: Pulsed Laser Control for Solid-State Spin Qubits

Executive Summary

This research validates a crucial methodology for advancing solid-state quantum technologies by demonstrating high-fidelity spin control using synchronized optical pulses. The key findings and implications for 6CCVD customers are summarized below:

Enhanced Coherence: Pulsed laser operation significantly improves the phase coherence time (T₂) of NV centers in 6H-SiC (e.g., 73.9 µs pulsed vs. 53.4 µs continuous wave at 50 K), confirming that precise optical control is essential for maintaining qubit fidelity.
Material Validation: The study successfully utilized key wide-band-gap materials—Single Crystal Diamond (SCD), Silicon Carbide (SiC), and Hexagonal Boron Nitride (hBN)—as host matrices for optically active spin centers (NV and V_B).
Decoherence Mitigation: The use of short, synchronized optical pulses (405-1064 nm) minimizes local sample heating and suppresses charge noise fluctuations, which are primary decoherence channels in semiconductor qubits.
Quantum Memory Focus: The methodology facilitates high-resolution Electron Nuclear Double Resonance (ENDOR) spectroscopy, enabling the investigation of weak electron-nuclear interactions necessary for developing long-lived quantum memory utilizing nuclear spins.
Cost-Effective Control: The development of a low-cost, high-precision pulse sequence programmer (based on STM32F373 microcontroller) makes advanced multi-pulse quantum experiments more accessible for research groups.
6CCVD Relevance: Replicating and extending this high-fidelity research requires ultra-high-purity, low-defect SCD substrates, which are 6CCVD’s core specialty, ensuring minimal intrinsic noise sources.

Technical Specifications

The following hard data points were extracted from the experimental setup and results, highlighting the precision required for quantum spin control:

Parameter	Value	Unit	Context
EPR Operating Frequency	94	GHz	W-band spectroscopy
MW Pulse Duration (π/2)	36 - 44	ns	Required for 90° spin rotation
RF Generator Power (ENDOR)	150	W	Used for Mims pulse sequence
Laser Wavelength Range	405 - 1064	nm	Visible to Near-Infrared excitation
SiC Sample Dimensions	0.45 x 0.45 x 0.67	mm³	Isotopically enriched 6H-²⁸SiC
Diamond Sample Dimensions	2 x 1 x 0.30	mm³	HPHT SCD, 5 x 10¹⁸ cm^-3 N impurities
Electron Irradiation Dose	4 x 10¹⁸	cm^-2	Used for defect generation in SiC
SiC Annealing Temperature	900	°C	In Argon atmosphere
T₂ (SiC, 50 K, CW Laser)	53.4 ± 0.2	µs	Phase coherence time (Continuous Wave)
T₂ (SiC, 50 K, Pulse Laser)	73.9 ± 0.4	µs	Phase coherence time (Pulsed Mode)
T₂ (Diamond, Dark Mode, 297 K)	1.910(8)	ms	Transverse relaxation time (Room Temperature)
Maximum Pulse Repetition Time	2.3 x 10⁹	µs	Programmer capability

Key Methodologies

The experiment focused on achieving precise temporal synchronization between optical and microwave/RF pulses to isolate spin dynamics from optical noise.

Spectroscopy Platform: Experiments utilized a Bruker Elexsys E680 spectrometer operating in pulsed mode at 94 GHz (W-band), coupled with a superconducting magnet (up to 6 T) and a flow helium cryostat (25 K to 300 K).
Pulse Sequence Generation: A custom pulse sequence programmer, built around an affordable 32-bit STM32F373 microcontroller, was implemented to generate stable, synchronized TTL pulses for laser control.
Optical Synchronization: The programmer was configured to shift the start of the microwave/RF sync pulse relative to the laser pulse (e.g., 100 µs shift) to ensure that the EPR/ENDOR measurements were performed in the “dark” state, immediately following spin initialization, minimizing light-induced decoherence.
Defect Initialization: Spin centers (NV in Diamond/SiC, V_B in hBN) were initialized using short optical pulses (405-1064 nm) via intersystem crossing (ISC) to preferentially populate the M_S = 0 ground state.
Relaxation Measurement: Transverse magnetization decay (T₂) was measured using the two-pulse Hahn echo sequence (π/2 - τ - π - τ - ESE). Electron-nuclear interactions were probed using the Mims ENDOR sequence (π_MW/2 - τ - π_RF - π_MW/2 - τ - ESE).
Sample Preparation: Samples (SiC, Diamond, hBN) were irradiated with 2 MeV electrons (dose up to 6 x 10¹⁸ cm^-2) to create vacancy defects, followed by high-temperature annealing (up to 900 °C) for defect activation and stabilization.

6CCVD Solutions & Capabilities

The successful replication and scaling of this quantum research depend critically on the quality and customization of the host materials. 6CCVD provides the necessary high-specification MPCVD diamond and related materials to meet these stringent requirements.

Applicable Materials

Research Requirement	6CCVD Solution	Technical Specification
High-Purity SCD Diamond	Optical Grade Single Crystal Diamond (SCD)	Ultra-low intrinsic nitrogen content (< 1 ppb) to maximize T₂ coherence times and ensure a stable environment for externally implanted NV centers.
SiC Substrates	Custom SCD/PCD SiC Substrates	High-purity SiC material (SCD or PCD) ready for isotopic enrichment or external electron irradiation/ion implantation for controlled defect generation.
Alternative Qubit Platforms	Boron-Doped Diamond (BDD)	Available for researchers exploring alternative solid-state spin systems or utilizing BDD as high-conductivity electrodes for integrated quantum devices.
Surface Quality	Polished SCD Wafers	SCD surfaces polished to Ra < 1 nm, crucial for minimizing surface defects and charge noise that contribute to spectral diffusion and decoherence.

Customization Potential

The W-band EPR experiments utilized small, custom-sized samples (e.g., 0.45 x 0.45 x 0.67 mm³ SiC, 2 x 1 x 0.30 mm³ Diamond) to fit the high-frequency resonator. 6CCVD excels at providing materials tailored precisely for such demanding experimental setups:

Custom Dimensions: We supply SCD and PCD plates/wafers up to 125 mm in diameter, with in-house laser cutting and dicing services to produce custom sub-millimeter samples required for high-frequency EPR/ENDOR resonators.
Thickness Control: We offer precise thickness control for SCD (0.1 µm to 500 µm) and PCD (0.1 µm to 500 µm), allowing researchers to optimize the material volume for maximum filling factor and signal-to-noise ratio (S/N).
Integrated Metalization: For future device integration (e.g., creating on-chip microwave waveguides or electrodes for enhanced spin control), 6CCVD offers custom metalization services including Au, Pt, Pd, Ti, W, and Cu deposition directly onto the diamond or SiC surface.

Engineering Support

The paper highlights the complexity of optimizing material properties (purity, defect density, annealing) to achieve long coherence times. 6CCVD’s in-house team of PhD material scientists specializes in the growth and characterization of MPCVD diamond for quantum applications.

Material Selection for Quantum Projects: Our experts can assist researchers in selecting the optimal SCD grade (e.g., low-strain, low-nitrogen) and thickness required to replicate or extend high-fidelity quantum memory and sensing projects, ensuring the starting material minimizes intrinsic decoherence sources.
Global Logistics: We ensure reliable, global delivery of sensitive materials, offering DDU (default) and DDP shipping options to streamline procurement for international research collaborations.

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

View Original Abstract

Quantum technologies are currently being explored for various applications, including computing, secure communication, and sensor technology. A critical aspect of achieving high-fidelity spin manipulations in quantum devices is the controlled optical initialization of electron spins. This paper introduces a low-cost programming scheme based on a 32-bit STM32F373 microcontroller, aimed at facilitating high-precision measurements of optically active solid-state spin centers within semiconductor crystals (SiC, hBN, and diamond) utilizing a multi-pulse sequence. The effective shaping of short optical pulses across semiconductor and solid-state lasers, covering the visible to near-infrared range (405-1064 nm), has been validated through photoinduced electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) spectroscopies. The application of pulsed laser irradiation influences the EPR relaxation parameters associated with spin centers, which are crucial for advancements in quantum computing. The presented experimental approach facilitates the investigation of weak electron-nuclear interactions in crystals, a key factor in the development of quantum memory utilizing nuclear qubits.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi16040396

References

2018 - Material Platforms for Spin-Based Photonic Quantum Technologies [Crossref]
2004 - Low Temperature Annealing of Electron Irradiation Induced Defects in 4H-SiC [Crossref]
2018 - Controlled Generation of Intrinsic Near-Infrared Color Centers in 4H-SiC via Proton Irradiation and Annealing [Crossref]
2018 - Defects Related to Electrical Doping of 4H-SiC by Ion Implantation [Crossref]
2022 - Ultrafast Pulsed Laser Stealth Dicing of 4H-SiC Wafer: Structure Evolution and Defect Generation [Crossref]
2023 - NV-Centers in SiC: A Solution for Quantum Computing Technology? [Crossref]
2016 - Spin Centres in SiC for Quantum Technologies [Crossref]
2022 - Silicon Carbide Photonics Bridging Quantum Technology [Crossref]
2020 - Chapter One—Color Centers in Diamond for Quantum Applications [Crossref]