Ultrathin fiber-taper coupling with nitrogen vacancy centers in nanodiamonds at cryogenic temperatures
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-12-02 |
| Journal | Optics Letters |
| Authors | Masazumi Fujiwara, Hong-Quan Zhao, Tetsuya Noda, Kazuhiro Ikeda, Hitoshi Sumiya |
| Institutions | Hokkaido University, Sumitomo Electric Industries (Japan) |
| Citations | 31 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Ultrathin Fiber-Taper Coupling with NV Centers
Section titled âTechnical Documentation & Analysis: Ultrathin Fiber-Taper Coupling with NV CentersâThis document analyzes the research detailing the successful cryogenic operation of nitrogen vacancy (NV) center/nanofiber hybrid systems, providing technical specifications and outlining how 6CCVDâs advanced MPCVD diamond materials and engineering services can accelerate and enhance similar quantum information and metrology projects.
Executive Summary
Section titled âExecutive SummaryâThe research successfully demonstrates a critical step toward fiber-integrated quantum devices by operating nanodiamond-coupled fiber tapers at cryogenic temperatures.
- Cryogenic Breakthrough: First successful demonstration of cooling fragile NV/nanofiber hybrid systems to a stable operating temperature of 9 K.
- Material Precursor: Nanodiamonds containing multiple NV centers were derived from Type Ib bulk diamond synthesized under high-pressure, high-temperature (HPHT) conditions (5.5 GPa, 1350 °C).
- Enhanced Coupling: Fluorescence from the NV centers was efficiently channeled into the single guided mode of the 480 nm nanofiber, achieving a photon count rate three times higher than detection via a high-NA objective lens.
- Quantum Application: The system provides a robust testbed for NV-based quantum information devices (e.g., quantum memories, phase gates) and highly sensitive nanoscale magnetometry in cryogenic environments.
- Spectroscopic Confirmation: Characteristic sharp zero-phonon lines (ZPLs) were observed for both neutral (NVâ° at 577 nm) and negatively charged (NVâ» at 639 nm) centers, confirming the high quality of the NV emission at 9 K.
- 6CCVD Value Proposition: 6CCVD specializes in high-purity MPCVD Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD), offering superior material control (especially nitrogen doping) necessary to optimize NV center creation and coherence times beyond the capabilities of the HPHT precursor used in this study.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental methodology and results:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Stable Operating Temperature | 9 | K | Achieved using optimized cooling speed in LHe flow cryostat. |
| Nanofiber Diameter | 480 | nm | Subwavelength region used for nanodiamond deposition. |
| HPHT Synthesis Pressure (Precursor) | 5.5 | GPa | Used for Type Ib bulk diamond growth. |
| HPHT Synthesis Temperature (Precursor) | 1350 | °C | Used for Type Ib bulk diamond growth. |
| Nitrogen Concentration (Precursor) | ~100 | ppm | Estimated in synthetic Type Ib crystals (via FT-IR). |
| Electron Irradiation Dose | 100 | kGy | Used to create NV centers (4.6 MeV beam). |
| Annealing Temperature | 800 | °C | Post-irradiation treatment (1 hour in vacuo). |
| Nanodiamond Particle Size Range | 500 nm to 2.0 | ”m | Range observed via SEM. |
| Neutral NV ZPL Wavelength (NVâ°) | 577 | nm | Zero-phonon line observed at 4.2 K. |
| Negative NV ZPL Wavelength (NVâ») | 639 | nm | Zero-phonon line observed at 4.2 K. |
| Taper Detection Photon Rate | 551 | kHz | Detected photon count rate (3x objective detection). |
| Objective Detection Photon Rate | 174 | kHz | Detected photon count rate (NA=0.8 objective). |
| Theoretical Coupling Efficiency (Average) | 15.4 | % | For 480 nm nanofiber (average of radial, azimuthal, and axial dipoles). |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relied on precise material synthesis and careful device integration to achieve cryogenic stability and efficient optical coupling.
- Diamond Precursor Synthesis: High-quality Type Ib bulk diamond was synthesized using a temperature-gradient method under high-pressure and high-temperature (HPHT) conditions (5.5 GPa and 1350 °C), resulting in a nitrogen concentration of approximately 100 ppm.
- NV Center Creation: Synthetic crystals were irradiated with a 4.6 MeV electron beam up to a dose of 100 kGy, followed by annealing at 800 °C for 1 hour in vacuo.
- Nanodiamond Preparation: The bulk diamond was crushed, separated, dispersed in ethanol, and sonicated to create a nanodiamond suspension with particle sizes ranging from 500 nm to 2.0 ”m.
- Fiber Taper Fabrication: Commercial single-mode optical fibers (Thorlabs, 630HP) were adiabatically tapered to achieve a subwavelength diameter of 480 nm, maintaining transmission > 0.9.
- Nanodiamond Deposition: Nanodiamond solution was deposited onto the nanofiber region using a dip-coating process, moving the fiber taper along its axis.
- Cryogenic Mounting Optimization: An asymmetric mounting holder was designed, using UV adhesives placed 10 mm and 25 mm from the center, enabling successful cooling to 9 K while conserving high optical throughput and preventing abrupt breakage.
- Cryogenic Operation: The device was cooled in an LHe flow cryostat using an optimized slow cooling speed (e.g., -6 K hâ»Âč below 20 K) to prevent thermal expansion damage, achieving a temperature stability of ±0.05 K at 9 K.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD provides the advanced MPCVD diamond materials and customization services necessary to replicate this research using higher-quality substrates, or to extend it toward integrated quantum circuits and commercial sensors.
Applicable Materials
Section titled âApplicable MaterialsâThe use of HPHT Type Ib diamond as a precursor limits the ultimate coherence time and spectral stability of the NV centers. 6CCVD offers superior MPCVD alternatives:
| Material Recommendation | Description & Advantage |
|---|---|
| High-Purity SCD (Single Crystal Diamond) | Provides extremely low background impurity levels (e.g., < 1 ppb N), essential for creating high-quality NVâ» centers with long spin coherence times (T2), critical for quantum memory and phase gate applications. |
| Controlled Nitrogen Doped SCD | 6CCVD can precisely control nitrogen concentration (from ppb to 100s of ppm) during MPCVD growth, allowing researchers to optimize the NV center density and the crucial NVâ°/NVâ» ratio for specific optical coupling experiments. |
| Optical Grade PCD (Polycrystalline Diamond) | Available in large formats (up to 125 mm diameter) for high-throughput processing or for applications where large-area coverage is prioritized over single-crystal coherence. |
| Boron-Doped Diamond (BDD) | Available for researchers exploring alternative solid-state defects or requiring conductive diamond layers for integrated electrical control (e.g., Stark tuning of NV centers). |
Customization Potential
Section titled âCustomization PotentialâThe integration of nanodiamonds onto fragile fiber tapers highlights the need for precise material handling and custom geometry. 6CCVD supports the entire device fabrication chain:
- Custom Dimensions & Thickness: We provide SCD and PCD plates in custom dimensions up to 125 mm (PCD) and thicknesses ranging from 0.1 ”m to 500 ”m (SCD/PCD). This is ideal for researchers developing top-down fabrication methods (e.g., etching, milling) to create uniform micro- or nanodiamond structures superior to the crushed particles used in the paper.
- Ultra-Precision Polishing: Our SCD substrates are polished to an industry-leading surface roughness of Ra < 1 nm. This ultra-smooth surface is critical for minimizing optical scattering and surface-related decoherence when integrating diamond close to subwavelength structures. Inch-size PCD can be polished to Ra < 5 nm.
- Integrated Metalization: For future NV-based quantum devices requiring electrical control (e.g., applying electric fields for Stark shifts or creating microwave antennas), 6CCVD offers in-house metalization services, including Au, Pt, Pd, Ti, W, and Cu deposition.
Engineering Support
Section titled âEngineering Supportâ6CCVD acts as a technical partner, not just a supplier.
- Expert Consultation: 6CCVDâs in-house PhD team can assist researchers in optimizing material selection and post-processing recipes (e.g., irradiation and annealing parameters) specifically for cryogenic quantum metrology and quantum information projects, ensuring the highest possible NV center yield and performance.
- Global Logistics: We offer reliable global shipping (DDU default, DDP available) to ensure rapid delivery of custom diamond substrates to international research facilities.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
We demonstrate cooling of ultrathin fiber tapers coupled with nitrogen vacancy (NV) centers in nanodiamonds to cryogenic temperatures. Nanodiamonds containing multiple NV centers are deposited on the subwavelength 480-nm-diameter nanofiber region of fiber tapers. The fiber tapers are successfully cooled to 9 K using our home-built mounting holder and an optimized cooling speed. The fluorescence from the nanodiamond NV centers is efficiently channeled into a single guided mode and shows characteristic sharp zero-phonon lines (ZPLs) of both neutral and negatively charged NV centers. The present nanofiber/nanodiamond hybrid systems at cryogenic temperatures can be used as NV-based quantum information devices and for highly sensitive nanoscale magnetometry in a cryogenic environment.