Quantum Photonic Interface for Tin-Vacancy Centers in Diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-07-26 |
| Journal | Physical Review X |
| Authors | Alison E. Rugar, Shahriar Aghaeimeibodi, Daniel Riedel, Constantin Dory, Haiyu Lu |
| Institutions | SLAC National Accelerator Laboratory, Stanford University |
| Citations | 95 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research reports the first successful integration and Purcell enhancement of Tin-Vacancy (SnV-) centers in a diamond photonic crystal cavity, establishing a highly efficient spin-photon interface critical for scalable quantum networks.
- High Efficiency Interface: The coupling of the SnV Zero-Phonon Line (ZPL) emission to a one-dimensional photonic crystal cavity resulted in a 40-fold increase in emission intensity.
- Strong Purcell Enhancement: The system achieved an experimental Purcell factor (FP) of 25 and a 10-fold reduction in the excited-state lifetime (from 7.0 ns to 0.69 ns).
- Near-Unity Coupling: The probability of an excited state decaying into the cavity mode via the ZPL (ÎČ factor) reached 90.1 ± 1.1%, enabling a ZPL photon creation rate greater than 1 GHz.
- Single Photon Source: Second-order autocorrelation measurements confirmed the enhanced SnV center acts as a single-photon source, with g(2)(0) = 0.29 ± 0.08.
- Scalability Advantage: SnV centers exhibit long spin coherence times accessible at temperatures above 1 K, eliminating the need for complex dilution refrigerators required by other platforms (like SiV centers), making this platform highly promising for practical quantum networks.
- Fabrication Method: Devices were fabricated using a scalable quasi-isotropic diamond undercut method combined with a shallow ion implantation and growth (SIIG) technique for precise SnV center generation.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Operating Temperature | ~5 | K | Cryogenic measurement environment |
| Cavity Type | 1D Photonic Crystal Nanobeam | N/A | Suspended diamond waveguide |
| Measured Quality Factor (Q) | 2135 ± 170 | N/A | Transmission measurement (Fig 1e) |
| Simulated Mode Volume (Vmode) | 0.56 (λ/η)3 | N/A | FDTD simulation |
| Waveguide Width (w) | 300 | nm | Cavity design parameter |
| Waveguide Thickness (h) | 200 | nm | Cavity design parameter |
| Cavity Resonance Wavelength (λres) | 619.6 | nm | Tuned to SnV C transition ZPL |
| SnV ZPL Wavelength (C transition) | 619.6 | nm | Highest count rate transition |
| Emission Intensity Enhancement | 40 ± 4 | fold | On-resonance vs. off-resonance (Fig 2b) |
| Maximum Saturation Intensity Contrast | Up to 30 | times | Resonant vs. off-resonant saturation data |
| Off-Resonance Lifetime (Ïoff) | 6.980 ± 0.078 | ns | Non-resonant radiative decay rate |
| On-Resonance Lifetime (Ïon) | 0.685 ± 0.014 | ns | Excited-state lifetime reduction (10.1 ± 1.2 fold) |
| Experimental Purcell Factor (FP) | 24.8 ± 3.0 | N/A | Corrected for non-unity radiative probability |
| Beta Factor (ÎČ) | 90.1 ± 1.1 | % | Probability of emission into cavity mode |
| Second-Order Autocorrelation (g(2)(0)) | 0.29 ± 0.08 | N/A | Confirms single-photon emission |
| Sn Ion Implantation Energy | 1 | keV | Shallow Ion Implantation and Growth (SIIG) |
| Sn Ion Implantation Dose | 5 x 1011 | cm-2 | SnV center generation |
| Diamond Overgrowth Thickness | 90 | nm | High-quality diamond film |
Key Methodologies
Section titled âKey MethodologiesâThe devices were fabricated on electronic-grade single-crystalline diamond using a combination of shallow ion implantation and quasi-isotropic etching techniques.
1. SnV Center Generation (Shallow Ion Implantation and Growth - SIIG)
Section titled â1. SnV Center Generation (Shallow Ion Implantation and Growth - SIIG)â- Substrate Preparation: The diamond chip (Element Six) was cleaned in a boiling tri-acid solution (1:1:1 Sulfuric/Nitric/Perchloric acids). The top 500 nm was removed via O2 plasma etch.
- Implantation: 120Sn+ ions were implanted shallowly at 1 keV with a dose of 5 x 1011 cm-2.
- Overgrowth (CVD): A 90 nm high-quality diamond film was subsequently grown using Microwave Plasma Chemical Vapor Deposition (MPCVD) under the following conditions:
- Stage Temperature: 650° C
- Microwave Power: 1100 W
- Pressure: 23 Torr
- Gas Flow: 300 sccm H2, 0.5 sccm CH4
2. Nanophotonic Cavity Fabrication (Quasi-Isotropic Etching)
Section titled â2. Nanophotonic Cavity Fabrication (Quasi-Isotropic Etching)â- Masking: A 200 nm SixNy layer was grown and patterned via electron-beam lithography using hydrogen silsesquioxane (FOx-16) resist.
- Mask Etch: The SixNy was etched using SF6, CH4, and N2 Reactive Ion Etch (RIE).
- Diamond Etch (Anisotropic): The patterned SixNy mask was used for an anisotropic O2 RIE of the diamond substrate.
- Sidewall Passivation: 30 nm of Al2O3 was deposited via Atomic Layer Deposition (ALD). Horizontal Al2O3 planes were removed using Cl2, BCl2, and N2 RIE, leaving only the diamond sidewalls covered.
- Undercut (Quasi-Isotropic Etch): A second anisotropic O2 RIE exposed bare diamond sidewalls, followed by the critical quasi-isotropic O2 plasma etch step:
- Temperature: High temperature (300° C)
- Bias: Zero forward bias
- Power: High inductively coupled plasma (ICP) power
- Result: This etch preferentially undercuts the structure along the {110} planes, releasing the nanobeam waveguides.
3. Optical Characterization
Section titled â3. Optical Characterizationâ- Setup: Home-built confocal microscope setup at cryogenic temperatures (~5 K).
- Cavity Tuning: Argon gas condensation was used to red-shift the cavity resonance wavelength by increasing the effective refractive index of the device. Heating (local laser or heated stage) reversed the condensation.
- Lifetime Measurement: Time-Correlated Single Photon Counting (TCSPC) was used, exciting the SnV center with a pulsed supercontinuum laser (450 nm long-pass and 550 nm short-pass filters) and detecting the emission through a 568 nm long-pass filter and monochromator.
Commercial Applications
Section titled âCommercial ApplicationsâThe successful development of an efficient, coherent, and scalable spin-photon interface using SnV centers in diamond has direct implications for several high-growth quantum technology sectors:
- Quantum Networks and Communication:
- Quantum Repeaters: SnV centers serve as highly efficient quantum nodes, enabling long-distance entanglement distribution without the high decoherence rates associated with NV centers.
- Scalable Architectures: The high ÎČ factor (90%) ensures that the majority of emitted photons are channeled into the waveguide, maximizing coupling efficiency into optical fiber networks.
- Quantum Computing:
- Solid-State Qubits: SnV centers offer superior optical coherence compared to NV centers, making them excellent candidates for solid-state quantum memories and processors integrated into photonic circuits.
- Hybrid Integration: The demonstrated platform is compatible with on-chip photonic architectures, paving the way for large-scale quantum information processing systems.
- Quantum Sensing:
- High-Fidelity Readout: The strong Purcell enhancement facilitates fast, high-fidelity optical readout of the spin state, improving the performance of diamond-based quantum sensors.
- Diamond Material Science:
- Advanced CVD/Implantation: The SIIG method developed for precise, shallow placement of SnV centers (90 nm depth) is a key enabling technology for manufacturing high-performance diamond quantum devices.
View Original Abstract
The realization of quantum networks critically depends on establishing\nefficient, coherent light-matter interfaces. Optically active spins in diamond\nhave emerged as promising quantum nodes based on their spin-selective optical\ntransitions, long-lived spin ground states, and potential for integration with\nnanophotonics. Tin-vacancy (SnV$^{\,\textrm{-}}$) centers in diamond are of\nparticular interest because they exhibit narrow-linewidth emission in\nnanostructures and possess long spin coherence times at temperatures above 1 K.\nHowever, a nanophotonic interface for SnV$^{\,\textrm{-}}$ centers has not yet\nbeen realized. Here, we report cavity enhancement of the emission of\nSnV$^{\,\textrm{-}}$ centers in diamond. We integrate SnV$^{\,\textrm{-}}$\ncenters into one-dimensional photonic crystal resonators and observe a 40-fold\nincrease in emission intensity. The Purcell factor of the coupled system is 25,\nresulting in channeling of the majority of photons ($90\%$) into the cavity\nmode. Our results pave the way for the creation of efficient, scalable\nspin-photon interfaces based on SnV$^{\,\textrm{-}}$ centers in diamond.\n