Enhanced spectral density of a single germanium vacancy center in a nanodiamond by cavity integration

At a Glance

Metadata	Details
Publication Date	2023-07-10
Journal	Applied Physics Letters
Authors	Florian Feuchtmayr, Robert Berghaus, Selene Sachero, Gregor Bayer, Niklas Lettner
Institutions	Université de Tours, Centre National de la Recherche Scientifique
Citations	15
Analysis	Full AI Review Included

Enhanced Spectral Density of a Single Germanium Vacancy Center in a Nanodiamond by Cavity-Integration

Analysis by 6CCVD: Expert MPCVD Diamond Solutions

This research successfully demonstrates a critical step toward scalable quantum networks by integrating a single Germanium Vacancy (GeV^-) center nanodiamond into a high-finesse Fabry-Pérot (FP) microcavity. The achievement of a 48-fold Spectral Density Enhancement (SDE) confirms the viability of this robust, passively stable platform for efficient spin-photon interfaces.

Executive Summary

Core Achievement: Successful integration of a single GeV^- center nanodiamond (ND) into an open, tunable Fabry-Pérot microcavity using Atomic Force Microscope (AFM) nanomanipulation.
Performance Metric: Achieved a significant 48-fold Spectral Density Enhancement (SDE) of the GeV^- emission at room temperature.
Optical Quality: The assembled cavity maintained a high optical quality, demonstrating a finesse of F = 7,700.
Single Photon Purity: The GeV^- center proved to be a high-purity single photon source, confirmed by strong anti-bunching (g⁽²⁾(0) = 0.11 ± 0.04).
Methodology: Utilized a precise “pick and place” technique to align the 200 nm ND intrinsically with the cavity field, reducing technical overhead.
Future Potential: The platform is robust and stable, offering a promising path for extension to cryogenic temperatures to achieve higher Purcell factors (P > 50) and establish an efficient spin-photon quantum interface.

Technical Specifications

Parameter	Value	Unit	Context
Spectral Density Enhancement (SDE)	48 ± 20	Fold	Cavity vs. Free Space Emitter
Cavity Finesse (F)	7,700 ± 1,800	N/A	Achieved with ND integrated
Quality Factor (Q_Cav)	260,000 ± 60,000	N/A	Calculated for the cavity
Second-Order Correlation (g⁽²⁾(0))	0.11 ± 0.04	N/A	Single Photon Source Purity
ZPL Wavelength (ND in Cavity)	599.25 ± 0.03	nm	Zero Phonon Line
ZPL FWHM (ND in Cavity)	1.10 ± 0.04	nm	Spectral linewidth
Excited State Lifetime (τ_LT)	2.53 ± 0.20	ns	Free space measurement
Mode Volume (V)	140 ± 40	µm³	Calculated effective mode volume
Corrected Purcell Factor (P*)	0.28 ± 0.03	N/A	Calculated for room temperature operation
Nanodiamond Size (Transferred)	190 x 180 x 130	nm	Dimensions of the integrated ND

Key Methodologies

Diamond Synthesis: Germanium-doped nanodiamonds (NDs) were grown via High Pressure High Temperature (HPHT) synthesis under extreme conditions (1,450°C and 8 GPa).
Doping: Germanium Vacancy (GeV^-) centers were incorporated using Germanium triphenyl-chloride (GeC₁₈H₁₅Cl) as the doping component.
Cavity Mirror Fabrication: The concave mirror was fabricated by CO₂ laser ablation of a SiO₂ substrate, followed by the deposition of a Distributed Bragg Reflector (DBR) coating (minimum transmission T < 310 ppm at 601 nm).
Emitter Identification: Confocal microscopy (532 nm excitation) was used to identify single GeV^- centers with narrow ZPL emission and strong anti-bunching (g⁽²⁾(0) = 0.11).
Nanomanipulation: An Atomic Force Microscope (AFM) was used in a “pick and place” technique to transfer the pre-characterized 200 nm ND precisely into the center of the curved mirror structure.
Cavity Characterization: The assembled FP cavity was characterized via reflection signals to determine finesse and quality factor, and photoluminescence (PL) measurements were performed under off-resonant excitation (587.8 nm) to quantify SDE.

6CCVD Solutions & Capabilities

This research highlights the critical need for high-quality diamond materials and precise geometric control to realize robust quantum optical devices. 6CCVD specializes in providing the foundational MPCVD diamond substrates necessary to replicate and advance this work, particularly by transitioning from nanodiamonds to high-purity Single Crystal Diamond (SCD) membranes for enhanced stability and coherence at cryogenic temperatures.

Research Requirement	6CCVD Solution & Capability	Technical Advantage
Applicable Materials	Optical Grade SCD (0.1µm - 500µm thickness)	Provides superior crystalline quality and reduced strain compared to NDs, essential for achieving the Fourier Transform (FT) limit and maximizing the Purcell effect (P > 50) required for efficient quantum repeaters.
Custom Dimensions	SCD Plates/Wafers up to 125mm; Custom Laser Cutting	Enables the fabrication of large-area, high-uniformity SCD membranes (0.1µm to 500µm) suitable for direct integration into FP cavities or for creating robust photonic crystal waveguides (as referenced in the paper).
Surface Quality	Ultra-Low Roughness Polishing (Ra < 1nm for SCD)	Ensures minimal scattering losses when integrating the diamond surface directly into the optical resonator, crucial for maintaining high cavity finesse (F = 7,700).
Customization Potential	In-House Metalization (Ti, Pt, Au, Pd, W, Cu)	We offer custom metal deposition services, allowing researchers to apply precise metal contacts for potential electrical gating experiments or for creating integrated mirror structures directly on the diamond surface.
Advanced Doping	High-Purity SCD for Post-Growth Implantation	While the paper uses HPHT GeV^- NDs, 6CCVD supplies the ideal low-strain SCD host material for precise, controlled ion implantation of Group IV centers (SiV, GeV, SnV) necessary for scalable quantum device manufacturing.
Engineering Support	In-House PhD Team Consultation	6CCVD’s material scientists can assist with material selection, thickness optimization, and surface preparation protocols for similar Quantum Repeater Node or Spin-Photon Interface projects.

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

View Original Abstract

Color centers in diamond, among them the negatively charged germanium vacancy (GeV−), are promising candidates for many applications of quantum optics, such as a quantum network. For efficient implementation, the optical transitions need to be coupled to a single optical mode. Here, we demonstrate the transfer of a nanodiamond containing a single ingrown GeV− center with excellent optical properties to an open Fabry-Pérot microcavity by nanomanipulation utilizing an atomic force microscope. Coupling of the GeV− defect to the cavity mode is achieved, while the optical resonator maintains a high finesse of F=7700, and a 48-fold spectral density enhancement is observed. This article demonstrates the integration of a GeV− defect with a Fabry-Pérot microcavity under ambient conditions with the potential to extend the experiments to cryogenic temperatures toward an efficient spin-photon platform.

Tech Support

Original Source

DOI: https://doi.org/10.1063/5.0156787

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