Robust nano-fabrication of an integrated platform for spin control in a tunable microcavity
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2017-11-21 |
| Journal | APL Photonics |
| Authors | Stefan Bogdanovic, Madelaine S. Z. Liddy, Suzanne B. van Dam, Lisanne C. Coenen, Thomas Fink |
| Institutions | ETH Zurich, QuTech |
| Citations | 23 |
| Analysis | Full AI Review Included |
Technical Documentation and Analysis: Integrated Platform for NV Spin Control
Section titled âTechnical Documentation and Analysis: Integrated Platform for NV Spin ControlâExecutive Summary
Section titled âExecutive SummaryâThe research details a robust fabrication methodology for an integrated platform enabling microwave control of Nitrogen-Vacancy (NV) center electron spins within a high-finesse, tunable Fabry-PĂ©rot microcavity. This work directly addresses critical engineering challenges required for developing high-efficiency diamond-based quantum networks.
- Integrated Quantum Platform: Successfully developed a platform incorporating microwave striplines adjacent to a large-area, thin diamond membrane (8 ”m thickness) inside a DBR Fabry-Pérot cavity architecture.
- High Optical Preservation: The multi-step nano-fabrication process (including ICP RIE etching and metalization) did not compromise the optical quality of the planar DBR mirror, achieving a preserved cavity finesse of F = (20 ± 2) * 103.
- Microwave Spin Control Demonstrated: Successfully used the embedded Ti/Au striplines to address and control the NV electron spin, verified via Optically Detected Electron Spin Resonance (ODMR) at 2.87 GHz.
- Advanced Bonding Technique: Established a reliable Van der Waals bonding method for fixing large-area diamond membranes (2 mm x 2 mm) to the patterned mirror surface without adhesives, maintaining tight control over surface profile and minimizing scattering losses (final roughness 0.2 nm RMS).
- Material Necessity: The successful implementation relies entirely on high-purity, ultra-thin SCD/PCD diamond substrates with precisely polished surfaces (Ra < 1 nm required) to maintain high finesse and minimize scattering loss.
- Application Relevance: This integrated design paves the way for efficient quantum network nodes by utilizing the Purcell effect to enhance the NV centerâs resonant Zero-Phonon Line (ZPL) emission rate while retaining crucial spin control capabilities.
Technical Specifications
Section titled âTechnical SpecificationsâHard data extracted from the fabrication and measurement results.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Measured Cavity Finesse (Processed) | (20 ± 2) * 103 | Dimensionless | Maintained high-finesse post-processing |
| Mirror DBR Residual Transmission | †10 | ppm | Measured @ 637 nm after 300°C vacuum anneal |
| Diamond Membrane Thickness | 8 | ”m | Thin SCD/PCD slab integrated into the cavity |
| Diamond Membrane Area | 2 x 2 | mm | Demonstrated large-area bonding capability |
| Polished Fiber Curvature Radius (R) | 22.4 | ”m | Extracted from surface profile fitting |
| Fiber Tip Roughness (Ra) | †0.20 ± 0.02 | nm | Achieved via CO2 laser ablation technique |
| Final Diamond Surface Roughness | 0.2 | nm | RMS, achieved after Ar/Cl2 RIE treatment |
| Microwave Stripline Recess Depth | 65 | nm | Etched depth into the Ta2O5/SiO2 DBR stack |
| Stripline Metalization Stack | 5 nm Ti / 65 nm Au | nm | Adhesion/Conductive layers for microwave control |
| Planar Mirror Annealing Temperature | 300 | °C | Applied in vacuum for 5 hours to reduce absorption |
| NV Center Zero Field Splitting (Dgs) | 2.87 | GHz | Measured electron spin resonance frequency |
Key Methodologies
Section titled âKey MethodologiesâThe experiment relies on precision micro- and nano-fabrication techniques, specifically tailored to ensure thin-film integrity and ultra-low surface roughness.
- Fiber Dimple Fabrication:
- Method: CO2 laser ablation (1 ms circularly polarized pulse focused on cleaved fiber facet).
- Result: Concave depression with Ra †0.20 nm, controlling curvature R.
- DBR Mirror Coating:
- Layers: 31 alternating high (Ta2O5, 75 nm) and low (SiO2, 100 nm) refractive index layers.
- Substrate: Low roughness fused silica plates (Ra 0.5 nm RMS) and ablated fiber tips.
- Vacuum Annealing:
- Conditions: Vacuum, 300 °C, held for 5 hours.
- Purpose: Reduced absorption losses from â 50 ppm down to †10 ppm.
- Embedded Stripline Fabrication (ICP RIE & Metalization):
- Masking: 1 ”m thick AZ 3007 photoresist patterned (4 mm x 45 ”m lines).
- Etch Recipe (DBR Stack): SF6(Ar) / O2 ICP RIE, removing 65 nm of material (combined rate 1.9 nm/s).
- Metalization: Evaporation of 5 nm Titanium (Ti adhesion) followed by 65 nm Gold (Au).
- Liftoff: Overnight soak in photoresist stripper (PRS) at 70 °C.
- Diamond Membrane Preparation:
- Source Material: 0.5 mm thick (100) bulk diamond (Element Six).
- Slab Creation: Sliced and mechanically polished to 30 ”m, then thinned via chemical/etching.
- Cleaning/Smoothing: Boiling acid mixture (Perchloric : Nitric : Sulfuric) for 1 hour, followed by Ar/Cl2 based ICP RIE (500 W, 0.01 mBar, 30 °C) achieving a smooth surface profile and 0.2 nm RMS roughness.
- Van der Waals Bonding:
- Preparation: Processed mirror chip activated with Oxygen plasma (0.4 mbar, 100 W, 45 s).
- Bonding: Water pipetted onto the activated surface; diamond membrane placed on top; water evaporated using microscope objective light, promoting bonding via strong interfacial forces.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research highlights the critical need for ultra-precise, high-quality diamond engineering, a core specialization of 6CCVD. Our capabilities directly enable the replication and advancement of this integrated quantum architecture.
Applicable Materials
Section titled âApplicable MaterialsâThe foundation of this quantum platform requires high-purity material with controlled thickness and exceptional surface quality.
| Material Requirement | 6CCVD Recommended Solution | Key Advantage |
|---|---|---|
| Thin Membrane (8 ”m) | Optical Grade SCD (0.1”m - 500”m) | SCD ensures the highest possible material purity, necessary for long coherence times of the integrated NV centers. |
| Large-Area Substrate (2 x 2 mm) | High Purity PCD (Wafers up to 125mm) | For scaling the platform beyond lab-scale prototypes, 6CCVD offers large area PCD wafers that can be engineered with sufficient purity for integrated quantum defects. |
| NV Generation | Custom Doping/Implantation | We provide SCD substrates ready for NV creation, or precursor material suitable for controlled N-implantation necessary for maximizing ZPL emission uniformity. |
| Electrode Stability | Boron-Doped Diamond (BDD) | BDD substrates can be used for novel electrode designs or integrated heating elements (not used here but often useful in cavity systems), leveraging diamondâs stability and conductivity. |
Precision Engineering & Fabrication Support
Section titled âPrecision Engineering & Fabrication Supportâ6CCVDâs in-house capabilities meet and exceed the precision requirements detailed in this paper, enabling engineers to rapidly iterate on cavity designs.
| Service | Paper Requirement Match | 6CCVD Capability & Advantage |
|---|---|---|
| Custom Thickness | 8 ”m thin membrane | SCD/PCD thickness range from 0.1 ”m up to 500 ”m, allowing optimization of ZPL coupling efficiency and mechanical stability. |
| Ultra-Low Roughness | 0.2 nm RMS roughness | Standard SCD polishing to Ra < 1 nm, and leading PCD polishing capabilities down to Ra < 5 nm for inch-size wafers, crucial for minimizing scattering loss (100 ppm loss attributed to 0.5 nm roughness). |
| Metalization Stacks | 5 nm Ti / 65 nm Au striplines | Internal, cleanroom-standard deposition capabilities for Au, Pt, Pd, Ti, W, Cu, allowing rapid prototyping of custom multi-layer striplines, markers, and contacts. |
| Patterning & Etching | RIE recess etching of 65 nm | Full engineering support for defining micron-scale features via advanced lithography and RIE techniques, ensuring precise integration of microwave structures into the diamond surface or underlying DBR. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house PhD team can assist with material selection and processing specifications for similar Cavity-Enhanced NV Spin Control projects, ensuring material purity, surface roughness, and thickness tolerances are optimized for high-finesse operation and quantum coherence. We facilitate global delivery with DDU (default) and DDP options available.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Coupling nitrogen-vacancy (NV) centers in diamonds to optical cavities is a promising way to enhance the efficiency of diamond-based quantum networks. An essential aspect of the full toolbox required for the operation of these networks is the ability to achieve the microwave control of the electron spin associated with this defect within the cavity framework. Here, we report on the fabrication of an integrated platform for the microwave control of an NV center electron spin in an open, tunable Fabry-PĂ©rot microcavity. A critical aspect of the measurements of the cavityâs finesse reveals that the presented fabrication process does not compromise its optical properties. We provide a method to incorporate a thin diamond slab into the cavity architecture and demonstrate the control of the NV center spin. These results show the promise of this design for future cavity-enhanced NV center spin-photon entanglement experiments.