Coherence of a charge stabilised tin-vacancy spin in diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-04-28 |
| Journal | npj Quantum Information |
| Authors | Johannes Görlitz, Dennis Herrmann, Philipp Fuchs, Takayuki Iwasaki, Takashi Taniguchi |
| Institutions | Saarland University, Element Six (United Kingdom) |
| Citations | 56 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research unveils and exploits the charge cycle of the tin-vacancy (SnV-) center in diamond, overcoming a critical limitation (fluorescence termination) for Quantum Information Processing (QIP).
- Charge Stabilization Breakthrough: A single-photon charge cycle mechanism is identified. Applying a continuous wave 445 nm laser rapidly and efficiently stabilizes the desired negative charge state (SnV-).
- High Efficiency Initialisation: The charge initialisation process achieves a saturation efficiency of 91(1) % and can be completed rapidly, demonstrating initialisation times as fast as ~10 ”s.
- Enhanced Coherence: The charge-stabilized SnV- exhibits a ground state spin dephasing time (T2) of 5(1) ”s at 1.7 K, competitive with other Group IV-vacancy (G4V) centers.
- Long-Term Stability: Optical transitions maintain exceptional long-term stability, showing spectral fluctuations with a standard deviation of less than 4(2) MHz over one hour, well below the lifetime-limited linewidth (25 MHz).
- High-Fidelity Readout: Proof-of-principle single-shot spin state readout achieved a fidelity of 74 %, demonstrating highly cycling optical transitions even when the magnetic field is applied at a large angle (54.7°) to the defect axis.
- Universal Applicability: The proposed charge cycle model and stabilization method are suggested to be universal for other G4V centers (SiV, GeV) in diamond.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Spin Dephasing Time (T2) | 5(1) | ”s | Ground state, measured via CPT. |
| Spin Lifetime (T1) | > 20 | ms | At 200 mT and 1.7 K. |
| Charge Initialisation Efficiency | 91(1) | % | Saturation value using 445 nm laser. |
| Rapid Initialisation Time | ~10 | ”s | Achieved at highest 445 nm laser power. |
| Initialisation Time Constant (Tau) | 780(27) | ”s | Exponential fit of initialisation efficiency growth. |
| Single Shot Readout Fidelity | 74 | % | Total fidelity, threshold set at 1 photon count. |
| Spectral Stability (Std. Dev.) | < 4(2) | MHz | Low power PLE, charge stabilized, over 1 hour. |
| Power Broadened Linewidth | 88(2) | MHz | High power PLE (10 nW excitation). |
| Base Temperature | ~1.7 | K | Closed cycle helium cryostat operation. |
| Magnetic Field (B) | 0.2 | T | Applied at 54.7° relative to defect axis for CPT/Readout. |
| SnV ZPL Energy | 2.0 | eV | Resonant excitation wavelength (~620 nm). |
| Charge Repump Wavelength | 445 | nm | Optimized wavelength for SnV- stabilization (2.8 eV). |
| Charge Transfer Rate (Slope) | 1.28(5) | Hz/nW | Linear dependence on resonant excitation power (single photon process). |
Key Methodologies
Section titled âKey MethodologiesâThe SnV- centers were created and characterized using a combination of high-precision material synthesis and advanced optical spectroscopy techniques under cryogenic conditions.
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Sample Preparation (NI58):
- Substrate: (001) electronic grade bulk diamond (Element Six), low nitrogen (< 5 ppb) and boron (< 1 ppb) concentration.
- Implantation: Tin ions implanted at 700 keV energy.
- Fluence: 8 x 1013 ions/cm2.
- Annealing (HPHT): Subsequent high-pressure-high-temperature annealing performed at 2100 °C and 7.7 GPa to reduce implantation damage and form SnV centers.
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Cryogenic Setup:
- Measurements conducted in a home-built confocal microscope using a closed cycle helium cryostat (attodry2100) operating at a base temperature of ~1.7 K.
- High numerical aperture (NA 0.9) objective used for photon collection.
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Optical Excitation and Stabilization:
- Resonant Excitation: Continuous wave Dye laser (Matisse 2DS) stabilized using a wavemeter (WS6-200).
- Charge Stabilization: Continuous wave diode laser (Cobolt 06-MLD) emitting at 445 nm was used as the charge repump source.
- Charge Cycle Investigation: A pulsed supercontinuum laser (SuperK FIANIUM) was used to scan wavelengths from 420 nm to 580 nm to identify the optimal charge repump threshold (found at > 2.4 eV).
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Spin Coherence Measurement (CPT):
- Coherent Population Trapping (CPT) was performed all-optically to probe ground state spin coherence.
- Optical sidebands were generated using an Electro-Optical Phase Modulator (EOM, WPM-K0620) driven by a microwave generator (mg3692c).
- A magnetic field of 0.2 T was applied to lift spin state degeneracy.
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Single Shot Readout:
- A proof-of-principle single-shot readout sequence was implemented using two microwave generators (SG384) and switches to create sidebands resonant with both spin-conserving (SC) transitions (A1 and B2).
Commercial Applications
Section titled âCommercial ApplicationsâThe development of a stable, coherent, and efficiently readable SnV- spin qubit is highly relevant for several emerging quantum technologies:
- Quantum Computing (QIP): SnV- centers serve as promising solid-state spin qubits due to their long coherence times (T2 = 5 ”s) and lifetime-limited optical transitions, crucial for building quantum registers and processors.
- Quantum Networking and Communication: The high indistinguishability potential of photons emitted from charge-stabilized SnV- centers is essential for generating entangled photons and establishing quantum links between remote nodes.
- Quantum Sensing: Stable, coherent spin centers in diamond can be used for high-sensitivity magnetic field or temperature sensing, leveraging the long T1 time (> 20 ms).
- Integrated Photonics: The SnV- centerâs compatibility with diamond nanophotonic structures (waveguides, micropillars, photonic crystal cavities) makes it ideal for developing integrated quantum photonic interfaces.
- Diamond Material Science: The detailed understanding of the charge cycle (involving divacancies and charge traps) provides critical insight for optimizing diamond growth and defect engineering recipes for QIP applications.
View Original Abstract
Abstract Quantum information processing (QIP) with solid state spin qubits strongly depends on the efficient initialisation of the qubitâs desired charge state. While the negatively charged tin-vacancy (SnV â ) centre in diamond has emerged as an excellent platform for realising QIP protocols due to long spin coherence times at liquid helium temperature and lifetime limited optical transitions, its usefulness is severely limited by termination of the fluorescence under resonant excitation. Here, we unveil the underlying charge cycle, potentially applicable to all group IV-vacancy (G4V) centres, and exploit it to demonstrate highly efficient and rapid initialisation of the desired negative charge state of single SnV centres while preserving long term stable optical resonances. In addition to investigating the optical coherence, we all-optically probe the coherence of the ground state spins by means of coherent population trapping and find a spin dephasing time of 5(1) ÎŒ s. Furthermore, we demonstrate proof-of-principle single shot spin state readout without the necessity of a magnetic field aligned to the symmetry axis of the defect.