Purcell-Enhanced Single-Photon Emission from Nitrogen-Vacancy Centers Coupled to a Tunable Microcavity
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-11-22 |
| Journal | Physical Review Applied |
| Authors | Hanno Kaupp, Thomas HĂźmmer, Matthias Mader, Benedikt Schlederer, Julia Benedikter |
| Institutions | University of Stuttgart, Ludwig-Maximilians-Universität Mßnchen |
| Citations | 102 |
| Analysis | Full AI Review Included |
Technical Analysis of Purcell-Enhanced Single-Photon Emission in Diamond Microcavities
Section titled âTechnical Analysis of Purcell-Enhanced Single-Photon Emission in Diamond MicrocavitiesâDocumentation Generated by 6CCVD â The Global Leader in MPCVD Diamond Solutions.
Executive Summary
Section titled âExecutive SummaryâThe research demonstrates a path toward highly efficient solid-state single-photon sources (SPS) by coupling Nitrogen-Vacancy (NV) centers in nanodiamonds to a tunable fiber-based Fabry-Perot microcavity. This work validates the critical role of ultra-small mode volume and precision-engineered diamond materials in quantum optics.
- Core Achievement: Demonstrated Purcell-enhanced single-photon emission using a tunable, open-access microcavity with an ultra-small mode volume ($1.0 \lambda^{3}$).
- Quantified Enhancement: An experimental effective Purcell factor ($C_{\text{eff}}$) of up to 2.0 was observed, corresponding to a 40% reduction in fluorescence lifetime (down to 11.2 ns).
- High Brightness: Photon collection rates reached $1.6 \times 10^{6} \text{ s}^{-1}$ from a single NV center, significantly exceeding free-space collection rates.
- Advanced Prediction: Numerical simulations predict ideal Purcell factors of up to 11 for optimized NV centers and up to 63 for Silicon Vacancy (SiV) centers, promising ultra-bright SPS.
- Material Impact: The study confirms that nanodiamond morphology (specifically 155 nm cubic structure) provides additional mode confinement, demonstrating a âwaveguide effectâ critical for achieving maximal $C_{\text{eff}}$.
- 6CCVD Relevance: This application requires ultra-high purity CVD diamond substrates and precision polishing/metalization services, core specialties of 6CCVD, to scale the technology beyond nanodiamonds.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Minimal Cavity Mode Volume ($V$) | $1.0 \lambda^{3}$ (0.34 $\mu$m$^{3}$) | $\lambda^{3}$ | Achieved using advanced laser machining. |
| Measured Effective Purcell Factor ($C_{\text{eff}}$) | 2.0 | Dimensionless | Maximal measured enhancement at 1.1 $\mu$m cavity length. |
| Theoretical Ideal $C_{\text{eff}}$ (NV Center) | Up to 11 | Dimensionless | Predicted for optimal geometry (155 nm diamond cube). |
| Theoretical Ideal $C_{\text{eff}}$ (SiV Center) | Up to 63 | Dimensionless | Predicted for narrow-band emitters. |
| Saturation Count Rate ($K_{\infty}$) | $6.9 \times 10^{5}$ | $\text{s}^{-1}$ | Raw count rate for NV1 emitter. |
| Photon Collection Rate (First Lens) | $1.6 \times 10^{6}$ | $\text{s}^{-1}$ | Accounting for 43% detection efficiency. |
| Cavity Finesse ($\mathcal{F}$) | $42 \pm 1$ | Dimensionless | Measured at $\lambda_{0} = 690 \text{ nm}$. |
| Mirror Reflectivities ($R$) | 96% and 88% | % | Silver coatings on fiber tip and planar mirror, respectively. |
| Shortest Measured Lifetime ($\tau_c$) | 11.2 | ns | Corresponds to 40% reduction from free-space lifetime ($\tau_{0} \approx 34 \text{ ns}$). |
| Optimal Nanodiamond Size (Simulated) | $\approx 155$ | nm | Cubic shape for maximal waveguide effect and $C_{\text{eff}}$. |
| Outcoupling Efficiency ($\eta_{c}$) | 51 | % | Fraction of photons leaving cavity through the planar mirror. |
Key Methodologies
Section titled âKey MethodologiesâThe experiment successfully combined advanced materials processing, nanoscale fabrication, and precision spectroscopy to achieve controlled light-matter interaction.
- Diamond Emitter Source: Commercial nanodiamonds (Van-Moppes, 100-200 nm distribution) containing naturally occurring NV centers were spin-coated or drop-cast onto the planar mirror substrate.
- Fiber Cavity Fabrication: Ultra-small concave mirrors were created on the tip of an optical fiber using advanced $\text{CO}_{2}$ laser machining to achieve a radius of curvature ($r_c$) of 90 $\mu$m and structure depth $z < 100 \text{ nm}$.
- Mirror Coating: A metal coating stack was applied: 60 nm silver (fiber tip) and 33 nm silver (planar mirror), both finished with a 20 nm glass capping layer to prevent oxidation, prioritizing low field penetration over maximum reflectivity to minimize mode volume ($V$).
- Tunable Mechanism: The microcavity (plano-concave Fabry-Perot) utilized a three-axis nanopositioning stage for spatial scanning and a piezo actuator for dynamic, continuous tuning of the mirror separation ($d$) down to sub-$\mu$m gaps ($\lambda_{0}/2$ minimum).
- Characterization: Techniques included:
- Cavity-enhanced scanning fluorescence microscopy (to map emitters and determine mode waist $w_{0}$).
- Second-order correlation function $\text{g}^{(2)}(\tau)$ measurement (to confirm single-emitter purity, $\text{g}^{(2)}(0) = 0.27$).
- Time-correlated single photon counting (TCSPC) under pulsed excitation (to measure tunable fluorescence lifetime modification).
- Modeling and Prediction: Finite-Difference Time-Domain (FDTD) simulations were used to accurately model the complex dynamics (proximity effects, nanodiamond confinement) and predict optimal performance for both NV and SiV centers in optimized diamond geometries (e.g., 155 nm cube).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research highlights the critical need for highly controlled, high-purity diamond materials and specialized fabrication for the next generation of quantum light sources. 6CCVD offers the necessary expertise and manufacturing pipeline to advance this technology from proof-of-concept to integrated quantum devices.
Applicable Materials
Section titled âApplicable MaterialsâTo replicate and extend this research towards deterministic, high-yield quantum devices, 6CCVD recommends:
| Material Specification | Purpose in Quantum Cavities | 6CCVD Capability |
|---|---|---|
| Electronic Grade Single Crystal Diamond (SCD) | Deterministic Emitters: High-purity SCD allows for precise, low-damage implantation of NV or SiV centers (via $\text{N}_{2}$ or $\text{Si}$ ion beams) and subsequent annealing, enabling deterministic emitter placement crucial for scalability. | SCD plates up to 10 mm substrates; thickness control from $0.1 \mu\text{m}$ to $500 \mu\text{m}$. |
| Optical Grade Polycrystalline Diamond (PCD) | Large Area Planar Substrates: Required for the macroscopic planar mirror component, offering low auto-fluorescence and high thermal stability compared to glass. | PCD wafers up to 125 mm diameter; ideal for inch-size integrated optics. |
| Ultra-Low Roughness Substrates | High Finesse: Surface roughness must be minimized to achieve high cavity Finesse ($\mathcal{F}$) and reduce scattering loss (Ra must be minimized). | Polishing capability: SCD Ra < 1 nm; Inch-size PCD Ra < 5 nm. |
Customization Potential
Section titled âCustomization PotentialâThe success of the microcavity depends entirely on precision manufacturing and interface control. 6CCVD specializes in providing materials engineered for quantum applications:
- Custom Dimensions and Shaping: While this paper used commercial nanodiamonds, future optimization requires thin-film diamond membranes or structured diamond (e.g., pillars, waveguides, or optimized cubic structures) on insulating substrates. 6CCVD offers custom laser cutting and shaping services to meet precise geometry requirements for both thin films and thick substrates (up to 10 mm).
- Precision Polishing for Planar Mirrors: The planar mirror requires extremely low surface roughness to maintain high Finesse. 6CCVDâs proprietary polishing techniques guarantee $\text{Ra} < 1 \text{ nm}$ for SCD and $\text{Ra} < 5 \text{ nm}$ for large PCD substrates, exceeding the standard quality required for quantum optics interfaces.
- Advanced Metalization Stacks: The current work used $\text{Ag}$ coating with glass capping. 6CCVD provides in-house metalization services, including $\text{Ti}/\text{Pt}/\text{Au}$, $\text{Pd}$, $\text{W}$, and $\text{Cu}$. We can also work with clients to deposit specific high-reflectivity dielectric or hybrid (metal/dielectric) stacks required for optimized mode volume and outcoupling efficiency ($\eta_c$).
Engineering Support
Section titled âEngineering SupportâAchieving the predicted ideal Purcell factors (up to 63 for SiV) necessitates tight control over material properties, defect engineering, and integration geometry.
- Defect Engineering Consultation: Our in-house PhD material science team specializes in optimizing diamond crystal growth recipes and post-processing treatments to control the concentration and type of color centers (NV, SiV) for specific quantum applications.
- Thermal and Optical Modeling Support: We assist engineering teams in selecting the optimal diamond thickness and grade to minimize thermal load and maximize optical throughput for similar Purcell-enhanced Single-Photon Emitter projects.
- Global Supply Chain: We provide fast, reliable global shipping (DDU default, DDP available) to research facilities worldwide.
Call to Action: For custom specifications or material consultation necessary to unlock the full potential of diamond-based quantum light sources, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Optical microcavities are a powerful tool to enhance spontaneous emission of\nindividual quantum emitters. However, the broad emission spectra encountered in\nthe solid state at room temperature limit the influence of a cavity, and call\nfor ultra-small mode volume. We demonstrate Purcell-enhanced single photon\nemission from nitrogen-vacancy (NV) centers in nanodiamonds coupled to a\ntunable fiber-based microcavity with a mode volume down to $1.0\,\lambda^{3}$.\nWe record cavity-enhanced fluorescence images and study several single emitters\nwith one cavity. The Purcell effect is evidenced by enhanced fluorescence\ncollection, as well as tunable fluorescence lifetime modification, and we infer\nan effective Purcell factor of up to 2.0. With numerical simulations, we\nfurthermore show that a novel regime for light confinement can be achieved,\nwhere a Fabry-Perot mode is combined with additional mode confinement by the\nnanocrystal itself. In this regime, effective Purcell factors of up to 11 for\nNV centers and 63 for silicon vacancy centers are feasible, holding promise for\nbright single photon sources and efficient spin readout under ambient\nconditions.\n