Narrow-Linewidth Tin-Vacancy Centers in a Diamond Waveguide
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-08-03 |
| Journal | ACS Photonics |
| Authors | Alison E. Rugar, Constantin Dory, Shahriar Aghaeimeibodi, Haiyu Lu, Shuo Sun |
| Institutions | SLAC National Accelerator Laboratory, Stanford University |
| Citations | 58 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates the successful integration of high-quality, narrow-linewidth tin-vacancy (SnV-) quantum emitters into suspended diamond nanobeam waveguides, a critical step toward scalable quantum photonic circuits.
- Core Achievement: First demonstration of coupling SnV- centers to a nanophotonic waveguide, a fundamental building block for waveguide quantum electrodynamics.
- High Quality Emitters: Achieved near-lifetime-limited optical linewidths, with the narrowest measured at 36 ± 2 MHz.
- Fabrication Platform: The device relies on combining the Shallow Ion Implantation and Growth (SIIG) method for emitter generation with an advanced quasi-isotropic undercut etch technique for waveguide fabrication.
- Temperature Advantage: SnV- centers are promising candidates because they are expected to maintain long spin coherence times at temperatures above 1 K, potentially simplifying cooling requirements compared to SiV- systems.
- Device Structure: The resulting suspended waveguides are 400 nm wide, 280 nm thick, and 10 ”m long, featuring inverse-designed vertical couplers (VCs).
- Stability Analysis: The emitters exhibited instabilities, including blinking and spectral diffusion, quantified with a full width at half maximum (FWHM) of approximately 130 MHz.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Emitter Type | SnV- | N/A | Negatively charged tin-vacancy center |
| Minimum Linewidth | 36 ± 2 | MHz | Measured via Lorentzian fit (VC-to-VC configuration) |
| Average Linewidth | 36 ± 3 | MHz | Average across multiple SnV- centers |
| Operating Temperature (PLE) | 1.7 | K | Photoluminescence Excitation measurements |
| Implantation Ion | 120Sn+ | N/A | Used in the SIIG method |
| Implantation Energy | 1 | keV | Used for SnV- generation |
| Implantation Dose | 1.6 x 1010 | cm-2 | Used for SnV- generation |
| Emitter Depth | 90 | nm | Below the diamond surface (post-growth) |
| Waveguide Width | 400 | nm | Final suspended nanobeam dimension |
| Waveguide Thickness | 280 | nm | Final suspended nanobeam dimension |
| Waveguide Length | 10 | ”m | Final suspended nanobeam dimension |
| Spectral Diffusion (FWHM) | ~130 | MHz | Quantified via Gaussian fit to histogram |
| Non-resonant Excitation | 532 | nm | CW laser for PL mapping |
| Etch Mask 1 Material | SixNy | N/A | 200 nm thick, grown via PECVD |
| Etch Mask 2 Material | Al2O3 | N/A | 30 nm thick, grown via ALD |
Key Methodologies
Section titled âKey MethodologiesâThe integration relies on a multi-step nanofabrication process combining shallow ion implantation, diamond growth, and quasi-isotropic etching:
- Initial Cleaning and Etch: Electronic grade diamond (ElementSix) is cleaned in a boiling tri-acid solution, followed by an oxygen (O2) plasma etch to remove the top ~500 nm of the surface.
- Shallow Ion Implantation and Growth (SIIG):
- 120Sn+ ions are implanted at 1 keV with a dose of 1.6 x 1010 cm-2.
- The chip is cleaned with H2 plasma immediately before 90 nm of diamond is grown via Microwave-Plasma Chemical Vapor Deposition (MPCVD).
- Etch Mask Deposition and Patterning: 200 nm of SixNy is grown (PECVD) as an etch mask. The waveguide pattern is defined using electron-beam lithography (FOx-16) and transferred into the SixNy mask using SF6, CH4, and N2 Reactive Ion Etch (RIE).
- Anisotropic Diamond Etch: The diamond is etched using an anisotropic O2 RIE.
- Sidewall Protection: 30 nm of Al2O3 is grown via Atomic Layer Deposition (ALD). The horizontal planes of Al2O3 are removed using Cl2, BCl2, and N2 RIE. A second anisotropic O2 RIE exposes the vertical sidewalls of the diamond structure.
- Quasi-isotropic Undercut: The final release of the nanobeam is achieved using a quasi-isotropic O2 RIE. This step is performed at high temperature with high inductively coupled plasma power and the forward bias turned off, causing preferential etching along the {110} planes to undercut the structure.
- Mask Removal: The SixNy and Al2O3 etch masks are removed by soaking the sample in hydrofluoric acid (HF).
Commercial Applications
Section titled âCommercial ApplicationsâThe successful integration of high-quality SnV- centers into scalable photonic structures enables several advanced quantum technologies:
- Large-Scale Quantum Photonic Processors: Provides a fundamental, integrated platform for routing and manipulating photons on a chip, essential for scaling quantum computation architectures.
- High-Temperature Quantum Computing: SnV- centers are expected to function as robust qubits at temperatures above 1 K, reducing the complexity and cost associated with dilution refrigerator cooling required by other color centers (like SiV-).
- Quantum Network Infrastructure: Enables the development of on-chip spin-photon interfaces, crucial for creating quantum memory nodes and facilitating long-distance quantum communication.
- Quantum Nonlinear Optics: The narrow linewidth and strong coupling potential allow for advanced experiments such as spin-controlled photon switching and few-photon nonlinearity demonstrations.
- Deterministic Emitter Placement: The SIIG method is compatible with implantation masks, allowing for site-controlled generation of SnV- centers necessary for coupling multiple identical emitters to the same optical mode for superradiance experiments.
View Original Abstract
Integrating solid-state quantum emitters with photonic circuits is essential for realizing large-scale quantum photonic processors. Negatively charged tin-vacancy (SnV$^-$) centers in diamond have emerged as promising candidates for quantum emitters because of their excellent optical and spin properties including narrow-linewidth emission and long spin coherence times. SnV$^-$ centers need to be incorporated in optical waveguides for efficient on-chip routing of the photons they generate. However, such integration has yet to be realized. In this Letter, we demonstrate the coupling of SnV$^-$ centers to a nanophotonic waveguide. We realize this device by leveraging our recently developed shallow ion implantation and growth method for generation of high-quality SnV$^-$ centers and the advanced quasi-isotropic diamond fabrication technique. We confirm the compatibility and robustness of these techniques through successful coupling of narrow-linewidth SnV$^-$ centers (as narrow as $36\pm2$ MHz) to the diamond waveguide. Furthermore, we investigate the stability of waveguide-coupled SnV$^-$ centers under resonant excitation. Our results are an important step toward SnV$^-$-based on-chip spin-photon interfaces, single-photon nonlinearity, and photon-mediated spin interactions.