Electrical Tuning of Tin-Vacancy Centers in Diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-06-03 |
| Journal | Physical Review Applied |
| Authors | Shahriar Aghaeimeibodi, Daniel Riedel, Alison E. Rugar, Constantin Dory, Jelena VuÄkoviÄ |
| Institutions | Stanford University |
| Citations | 31 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Achievement: Demonstrated reversible electrical tuning of Tin-Vacancy (SnV-) centers in diamond using the direct-current (DC) Stark effect, achieving a tuning range exceeding 1.7 GHz.
- Performance Metric: The 1.7 GHz tuning range is approximately 57 times the natural transition linewidth (~30 MHz), sufficient to overcome typical inhomogeneous broadening in nanostructures (< 15 GHz).
- Stark Effect Characterization: Both quadratic (expected for inversion-symmetric defects) and linear (attributed to strain-induced broken symmetry) dependencies on the applied electric field were observed and quantified.
- Coefficient Magnitude: The measured Stark coefficients (change in dipole moment and polarizability) are several orders of magnitude smaller than those of non-inversion-symmetric color centers (e.g., NV-).
- Mechanism Validation: Careful control experiments confirmed that the observed frequency shift is genuinely due to the Stark effect, distinguishing it from parasitic thermal tuning caused by Joule heating, particularly below local fields of 40 MV/m.
- Fabrication Details: SnV centers were generated via 370 keV 120Sn+ ion implantation followed by high-temperature vacuum annealing (up to 1100°C) in electronic-grade diamond.
- Application Potential: This technique enables precise spectral matching of distinct SnV emitters, paving the way for multi-emitter quantum networks requiring indistinguishable photons.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Maximum Tuning Range | > 1.7 | GHz | Reversible shift of C transition |
| Natural Linewidth (E1) | 194 ± 12 | MHz | Measured at 0 V applied field |
| Operating Temperature | ~5 | K | Cryostat environment |
| SnV Implantation Energy | 370 | keV | 120Sn+ ions |
| SnV Implantation Dose | 2 x 1011 | cm-2 | Target depth ~90 nm (SRIM simulation) |
| High Annealing Temperature | 1100 | °C | Vacuum, 90 minutes |
| Ground State Splitting (E1) | 819.6 | GHz | Energy difference between C and D transitions |
| Polarizability Volume (E1, Îα / 4ÏΔ0) | 3.28 ± 0.18 | A3 | Quadratic Stark coefficient |
| Dipole Moment Change (E1, Δ) | 1.9 ± 1.1 x 10-4 | D | Residual linear Stark coefficient |
| Electrode Gap | 1 | ”m | Spacing between 4 ”m wide parallel electrodes |
| Maximum Local Field Tested | ~50 | MV/m | Achieved with 200 V applied voltage |
| Linewidth Broadening Threshold | 40 | MV/m | Onset of significant Joule heating effects |
Key Methodologies
Section titled âKey Methodologiesâ-
Diamond Preparation:
- Substrate: Electronic-grade, single-crystal diamond (Element Six).
- Cleaning: Boiling tri-acid solution (1:1:1 sulfuric/nitric/perchloric acids).
- Surface Etch: Removed top 300 nm of diamond using O2 plasma etch.
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SnV Center Generation:
- Implantation: 120Sn+ ion implantation (370 keV, 2 x 1011 cm-2).
- Annealing: Two-step vacuum annealing: 800°C (30 min) followed by 1100°C (90 min).
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Nanostructure and Electrode Fabrication:
- Mask Layer: 200 nm of silicon nitride (SixNy) grown via low-pressure chemical vapor deposition.
- Patterning: E-beam lithography using hydrogen silsesquioxane (FOx-16) resist.
- Diamond Etch: O2 plasma etch to create 500-nm tall diamond nanopillars and mesas.
- Electrode Definition: E-beam lithography (PMMA resist) followed by metal liftoff.
- Metal Stack: 5 nm Titanium (Ti) adhesion layer followed by 30 nm Gold (Au).
- Geometry: Parallel electrodes (4 ”m wide) placed 1 ”m apart, aligned along the [100] direction.
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Optical Characterization and Tuning:
- Setup: Home-built scanning confocal microscope in a cryostat (~5 K).
- Excitation: 532-nm continuous-wave laser for PL mapping; tunable laser for Photoluminescence Excitation (PLE) spectroscopy.
- Detection: Emission collected into the phonon sideband (PSB) using specific bandpass filters.
- Stark Tuning: DC voltage applied via a high-voltage power supply (Stanford Research Systems PS325).
- Data Analysis: Lorentzian fits applied to PLE spectra to extract shift, linewidth (FWHM), and intensity as a function of the local electric field (FLocal, approximated using COMSOL simulations).
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Joule Heating Control:
- Method 1 (External Emitter): Applied voltage to electrodes while monitoring an SnV center (Eout) located outside the electrode region to isolate thermal effects from leakage current.
- Method 2 (Stage Heating): Directly heated the cryostat stage up to ~20 K and monitored the frequency shift and FWHM of the primary emitter (E1) to characterize temperature dependence.
Commercial Applications
Section titled âCommercial ApplicationsâThe ability to precisely and reversibly tune the optical frequency of solid-state quantum emitters is critical for scalable quantum technologies.
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Quantum Networks and Repeaters:
- Enabling the realization of multiple, identical quantum nodes by compensating for fabrication-induced inhomogeneous spectral broadening.
- Crucial for achieving high-fidelity two-photon interference (HBT) between remote emitters.
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Quantum Information Processing:
- Multi-emitter quantum experiments requiring precise resonance matching between distinct qubits on the same chip.
- Dynamic stabilization of optical transition frequencies using feedback-based electric field tuning to counteract spectral diffusion.
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Integrated Photonics:
- Offers an alternative to electromechanical tuning (which is limited to freestanding waveguide structures) for controlling emitter frequency in integrated diamond devices.
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Quantum Sensing:
- While SnV centers are primarily spin qubits, the precise control over optical transitions is foundational for advanced quantum sensing protocols that rely on resonant excitation and readout.
View Original Abstract
Group-IV color centers in diamond have attracted significant attention as solid-state spin qubits because of their excellent optical and spin properties. Among these color centers, the tin-vacancy (Sn-V<sup>-</sup>) center is of particular interest because its large ground-state splitting enables long spin coherence times at temperatures above 1 K. However, color centers typically suffer from inhomogeneous broadening, which can be exacerbated by nanofabrication-induced strain, hindering the implementation of quantum nodes emitting indistinguishable photons. Although strain and Raman tuning have been investigated as promising tuning techniques to overcome the spectral mismatch between distinct group-IV color centers, other approaches need to be explored to find methods that can offer more localized control without sacrificing emission intensity. Here, we study the electrical tuning of Sn-V<sup>-</sup> centers in diamond via the direct-current Stark effect. We demonstrate a tuning range beyond 1.7 GHz. We observe both quadratic and linear dependence on the applied electric field. Further, we also confirm that the tuning effect we observe is a result of the applied electric field and is distinct from thermal tuning due to Joule heating. Stark tuning is a promising avenue toward overcoming detunings between emitters and enabling the realization of multiple identical quantum nodes.