Design and low-temperature characterization of a tunable microcavity for diamond-based quantum networks
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-04-24 |
| Journal | Applied Physics Letters |
| Authors | Stefan BogdanoviÄ, Suzanne van Dam, Cristian Bonato, Lisanne C. Coenen, Anne-Marije J. Zwerver |
| Institutions | ETH Zurich, QuTech |
| Citations | 55 |
| Analysis | Full AI Review Included |
Advanced Technical Documentation: Diamond Microcavities for Quantum Networking
Section titled âAdvanced Technical Documentation: Diamond Microcavities for Quantum NetworkingâReference Paper: Design and low-temperature characterization of a tunable microcavity for diamond-based quantum networks (arXiv:1612.02164v2)
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates a high-finesse, tunable Fabry-Perot (F-P) microcavity architecture enclosing a thin single-crystal diamond (SCD) membrane suitable for embedding Nitrogen-Vacancy (NV) quantum emitters. The findings are critical for scalable quantum network applications requiring enhanced photon generation and collection efficiency.
- Core Achievement: Demonstrated F-P cavity finesse ranging from F = 4,000 to F = 12,000 at cryogenic temperatures (11 K) using a diamond membrane.
- Material Specification: Successfully fabricated thin diamond membranes (â4 ”m thickness) exhibiting ultra-low surface roughness (0.35 nm RMS).
- Performance Limiter: The achieved finesse was primarily limited by scattering loss introduced by the diamond surface, highlighting the absolute necessity of sub-nanometer polishing.
- Quantum Enhancement: Modeling predicts that coupling NV centers to this cavity architecture boosts ZPL (Zero Phonon Line) emission probability into the cavity mode to over 80%, compared to 3% in uncoupled bulk diamond.
- Application Impact: The demonstrated enhancement in photon generation and collection efficiency is projected to yield an increase of approximately 10Âł times in remote quantum entanglement success rates.
- Cryogenic Stability: The tunable cavity demonstrated excellent mechanical stability, achieving a measured length stability of 0.48 nm at 11 K.
- Fabrication Process: Diamond membranes were prepared using Ar/Cl2 inductively coupled plasma Reactive Ion Etching (RIE) to preserve surface smoothness before Van der Waals bonding to the plane mirror.
Technical Specifications
Section titled âTechnical SpecificationsâThe following table summarizes the key physical and operational parameters extracted from the research characterizing the tunable F-P microcavity system.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Material Type | Single Crystal Diamond | N/A | Membrane for NV center hosting |
| Diamond Thickness (d) | â4 | ”m | Final etched membrane thickness |
| Surface Roughness (RMS) | 0.35 | nm | Measured on the diamond membrane via AFM |
| Operating Temperature (T) | 11 | K | Cryogenic environment for quantum operation |
| Achieved Cavity Finesse (F) | 4,000 - 12,000 | N/A | Measured at 11 K with diamond membrane |
| Expected Bare Finesse (F) | â29,000 | N/A | Based on mirror reflectivity (R â 99.99%) |
| Refractive Index (nd) | 2.417 | N/A | High refractive index used in model |
| Coupled ZPL Emission Probability | >80 | % | Simulated (ideal emitter placement) |
| Uncoupled ZPL Emission Probability | â3 | % | Bulk SCD reference value |
| Quantum Success Rate Boost | â10Âł | times | Estimated increase for entangling protocols |
| Cavity Displacement Stability | 0.48 | nm | Measured during low-vibration interval |
| Laser Input Frequency | 471.3 | THz | Diode laser used for linewidth measurement |
Key Methodologies
Section titled âKey MethodologiesâThe following process steps were essential for fabricating the high-performance diamond microcavity and characterizing its performance under cryogenic conditions:
- Diamond Membrane Fabrication: A 30 ”m polished SCD sheet (ElementSix) was thinned down to approximately 4 ”m using Ar/Cl2 Inductively Coupled Plasma RIE. This method was chosen specifically to maintain exceptionally low surface roughness (0.35 nm RMS).
- Plane Mirror Preparation: The thin diamond membrane was bonded to a high-reflectivity (R â 99.99%) plane mirror using Van der Waals forces.
- Concave Fiber Tip Fabrication: A concave fiber mirror (Radius of Curvature = 18.4 ”m) was manufactured using CO2 laser ablation and subsequently coated with a dielectric mirror stack (LASEROPTIK).
- Cryogenic Integration: The completed F-P cavity configuration (fiber tip facing the diamond/plane mirror assembly) was mounted inside a closed-cycle cryostat (Montana Instruments) capable of operation at 11 K.
- Mechanical Noise Mitigation: A high-frequency resonance cryo-positioning stage and a low-frequency passive vibration isolation stage were employed to mitigate mechanical noise generated by the cryostation pulse tube operation.
- Finesse and Linewidth Measurement: Narrow-linewidth diode laser light (471.3 THz) was coupled into the cavity. Cavity length was scanned via a piezo positioner, and transmission spectra were recorded to extract finesse and linewidth values at 300 K and 11 K.
- Quantum Prediction: The intrinsic cavity properties (Finesse, Purcell factor F) were used in conjunction with bulk NV parameters (ZPL branching ratio 3%, lifetime 12 ns) to simulate the excited state lifetime and emission probability into the cavity mode.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is uniquely positioned to supply the advanced diamond materials and engineering services required to replicate, scale, and extend the state-of-the-art research presented in this paper, particularly focusing on ultra-low scattering loss interfaces critical for achieving high finesse (F > 12,000).
Applicable Materials
Section titled âApplicable MaterialsâTo replicate the ultra-high-quality required for embedded NV centers and minimize optical scattering losses, 6CCVD recommends:
- Optical Grade Single Crystal Diamond (SCD): Required for hosting well-defined NV centers with bulk-like optical properties. Our standard SCD is grown via MPCVD, ensuring high purity necessary for quantum applications.
- Thickness Match: We can supply custom SCD wafers and plates ranging from 0.1 ”m to 500 ”m, perfectly covering the 4 ”m membrane thickness used in this study.
- Heavy Boron-Doped Diamond (BDD) Substrates: While not the active material, BDD substrates (up to 10 mm thickness) can be supplied for specialized heat sinking or integration platforms often used in complex cryogenic systems.
Customization Potential & Ultra-Polishing Services
Section titled âCustomization Potential & Ultra-Polishing ServicesâAchieving Finesse values above 12,000 is directly dependent on reducing the scatter loss introduced by the diamond surface (as noted by the authors, 0.35 nm RMS leads to F â 21,000 reduction). 6CCVD excels at meeting these demanding surface quality requirements.
| Research Requirement | 6CCVD Capability | Value Proposition |
|---|---|---|
| Ultra-Smooth Surfaces | SCD Polishing: Ra < 1 nm | Guaranteed surface roughness quality to minimize cavity scattering losses and maximize Finesse (F). Our polishing often achieves results comparable to or exceeding the 0.35 nm RMS requirement. |
| Custom Dimensions | Plates/Wafers up to 125 mm (PCD) | Ability to scale quantum device fabrication from lab-scale test pieces (Figure 1(b) scale: ~100 ”m) to production-ready platforms. |
| Thin Membrane Fabrication | SCD thickness control: 0.1 ”m - 500 ”m | Precise control over membrane dimensions, crucial for optimizing air-like vs. diamond-like mode coupling as defined by thickness d (Equation 1). |
| Integrated Functionality | Custom Metalization Services | In-house capability for depositing contact layers (Au, Pt, Pd, Ti, W, Cu). Useful for integrating electrostatic tuning electrodes or localized heating elements onto the mirror or diamond interfaces. |
| Precision Shaping | Custom Laser Cutting and Shaping | Providing custom shapes, patterns, or precise cleaving necessary for bonding or integration into complex cryostation mounts. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house team of PhD material scientists and technical engineers specializes in NV center technology and quantum applications. We offer comprehensive support in selecting the optimal SCD grade (high-purity, low-strain) and designing the required geometry (thickness and surface finish) to maximize Purcell enhancement and coherence times in similar diamond quantum emitter projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
We report on the fabrication and characterization of a Fabry-Perot microcavity enclosing a thin diamond membrane at cryogenic temperatures. The cavity is designed to enhance resonant emission of single nitrogen-vacancy centers by allowing spectral and spatial tuning while preserving the optical properties observed in bulk diamond. We demonstrate cavity finesse at cryogenic temperatures within the range of F=4000-12 000 and find a sub-nanometer cavity stability. Modeling shows that coupling nitrogen-vacancy centers to these cavities could lead to an increase in remote entanglement success rates by three orders of magnitude.