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

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2023-07-10
JournalApplied Physics Letters
AuthorsFlorian Feuchtmayr, Robert Berghaus, Selene Sachero, Gregor Bayer, Niklas Lettner
InstitutionsUniversité de Tours, Centre National de la Recherche Scientifique
Citations15
AnalysisFull AI Review Included

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

Section titled “Enhanced Spectral Density of a Single Germanium Vacancy Center in a Nanodiamond by Cavity-Integration”

Executive Summary

Section titled “Executive Summary”
  • Core Achievement: Demonstrated the successful integration of a single, high-quality Germanium Vacancy (GeV-) center within a 200 nm nanodiamond (ND) into a tunable, open Fabry-PĂ©rot (FP) microcavity using Atomic Force Microscope (AFM) nanomanipulation.
  • Performance Enhancement: Achieved a 48-fold Spectral Density Enhancement (SDE) of the GeV- zero phonon line (ZPL) emission at room temperature, attributed primarily to cavity funneling.
  • Cavity Quality: The assembled microcavity maintained exceptional optical quality, exhibiting a high finesse of F = 7,700 ± 1,800 and a quality factor of QCav = 260,000 ± 60,000.
  • Emitter Quality: The GeV- center demonstrated high-purity single-photon emission (g(2)(0) = 0.11 ± 0.04) and a narrow ZPL linewidth (1.24 nm) with a high Debye-Waller factor (>0.6).
  • Platform Stability: The system is passively stable and intrinsically aligned, reducing technical overhead and making it robust for extension to cryogenic temperatures, where a Purcell factor (P*) greater than 50 is anticipated.
  • Application Focus: This robust hybrid platform serves as a critical building block for efficient spin-photon interfaces necessary for scalable quantum networks and quantum repeater nodes.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
ND Synthesis Temperature1,450°CHigh Pressure High Temperature (HPHT)
ND Synthesis Pressure8GPaHPHT method
Nanodiamond Size (GeV-I)190 x 180 x 130nmAFM measurement (transferred ND)
ZPL Wavelength (Free Space)599.11 ± 0.03nmGreen excitation (532 nm)
ZPL FWHM (Free Space)1.24 ± 0.03nmCorresponds to QGeV = 483 ± 12
Excited State Lifetime (τLT)2.53 ± 0.20nsFree space emission
Second-Order Correlation (g(2)(0))0.11 ± 0.04-High-purity single photon source
Debye-Waller (DW) Factor>0.6-High ZPL emission fraction
Cavity Finesse (F)7,700 ± 1,800-Achieved value (Room temperature)
Cavity Quality Factor (QCav)260,000 ± 60,000-Calculated value
Cavity Mode Volume (V)(140 ± 40) (λ/n)3-Calculated value
Spectral Density Enhancement (SDE)48 ± 20-Cavity vs. Free Space (Room Temp)
Cavity Length (L)15.72 ± 0.06”mDetermined for resonance n=51
DBR Transmission Minimum (T)<310ppmAt 601 nm
Projected Purcell Factor (P)*>50-Potential at cryogenic temperatures

Key Methodologies

Section titled “Key Methodologies”
  1. GeV- Nanodiamond Synthesis:
    • NDs were synthesized using the HPHT method (1,450 °C, 8 GPa).
    • Carbon sources included detonation NDs, fluoroadamantane (C10H15F), and hepta-fluoronaphtalene (C10F8).
    • Germanium doping was achieved using Germanium triphenyl-chloride (GeC18H15Cl).
  2. Cavity Mirror Fabrication:
    • Concave mirror structures were created on a SiO2 substrate using a CO2 laser ablation process.
    • A Distributed Bragg Reflector (DBR) coating was applied, resulting in a low transmission minimum (<310 ppm) and forming a field antinode 62 nm into the diamond surface.
  3. Emitter Identification and Selection:
    • NDs were characterized on a sapphire substrate using a confocal microscope (532 nm excitation, NA = 0.9) and AFM imaging.
    • ND GeV-I was selected based on its narrow ZPL (1.24 nm) and strong anti-bunching (g(2)(0) = 0.11).
  4. Nanomanipulation and Integration (Pick and Place):
    • The AFM was used to transfer the ND GeV-I (approx. 200 nm size) from the sapphire substrate to the curved mirror structure.
    • A platinum cantilever was used for picking up the ND in contact mode.
    • The ND was precisely placed in the center of the curved mirror structure, ensuring intrinsic alignment with the cavity mode field maximum.
  5. Cavity Assembly and Tuning:
    • The curved mirror (containing the ND) and a second plane mirror (identical coating) were assembled to form the FP microcavity.
    • The cavity length (L) was tuned using a z-piezo nanopositioner attached to the plane mirror.
  6. Optical Characterization:
    • The cavity finesse (F) was extracted from the reflection signal by scanning the plane mirror piezo.
    • Photoluminescence (PL) was measured under off-resonant excitation (587.8 nm) to observe the cavity-modulated ZPL signal and calculate the Spectral Density (SD) and SDE.

Commercial Applications

Section titled “Commercial Applications”
  • Quantum Key Distribution (QKD): Provides high-rate, high-purity single-photon sources necessary for secure quantum communication protocols.
  • Quantum Repeaters and Networks: The robust, efficient spin-photon interface is a fundamental requirement for building scalable quantum repeater nodes, extending the range of quantum networks beyond 100 km.
  • Quantum Memory: The GeV- center, with its favorable spin properties at accessible cryogenic temperatures (below 1 K), serves as a promising solid-state quantum memory element.
  • Cavity Quantum Electrodynamics (cQED) Platforms: The high-Q, low-V FP microcavity platform is ideal for fundamental cQED experiments and for developing efficient quantum gates and state manipulation techniques.
  • Cryogenic Quantum Systems: The passively stable, intrinsically aligned platform, built with low thermal expansion components, is optimized for reliable operation in complex cryogenic environments required for achieving high Purcell factors (P* > 50).
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-PĂ©rot 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-PĂ©rot microcavity under ambient conditions with the potential to extend the experiments to cryogenic temperatures toward an efficient spin-photon platform.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2008 - The quantum internet [Crossref]
  2. 2009 - The security of practical quantum key distribution [Crossref]
  3. 2020 - Advances in quantum cryptography [Crossref]
  4. 2018 - Quantum internet: A vision for the road ahead [Crossref]
  5. 2009 - Quantum repeater with encoding [Crossref]
  6. 2006 - Repeat-until-success quantum computing using stationary and flying qubits [Crossref]
  7. 1998 - Quantum repeaters: The role of imperfect local operations in quantum communication [Crossref]
  8. 2003 - Optical microcavities [Crossref]
  9. 2020 - Cavity quantum electrodynamics with color centers in diamond [Crossref]
  10. 1946 - Spontaneous emission probabilities at radio frequencies [Crossref]

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