All-Optical Control of the Silicon-Vacancy Spin in Diamond at Millikelvin Temperatures
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2018-01-30 |
| Journal | Physical Review Letters |
| Authors | Jonas N. Becker, Benjamin Pingault, David GroĂ, Mustafa GĂŒndoÄan, Nadezhda Kukharchyk |
| Institutions | Element Six (United Kingdom), Saarland University |
| Citations | 128 |
| Analysis | Full AI Review Included |
Technical Analysis and Documentation for SiV Qubit Research
Section titled âTechnical Analysis and Documentation for SiV Qubit ResearchâExecutive Summary
Section titled âExecutive SummaryâThis research demonstrates a critical advance in solid-state quantum computing by achieving all-optical coherent control of the Silicon-Vacancy (SiV$^{-}$) electron spin, confirming its viability as an ultra-fast spin qubit.
- Qubit Control: Successful implementation of all-optical Rabi oscillations and control sequences (Ramsey, Hahn-echo) on the SiV$^{-}$ electron spin at millikelvin temperatures.
- Decoherence Mitigation: Cooling the HPHT Type IIa diamond sample to 12 mK suppressed phonon-induced decoherence, dramatically improving the spin relaxation time (T$_{1}^{spin}$) by a factor of 300, reaching 108(24) ”s.
- Coherence Achievement: A spin echo time (T${2,echo}$) of 138(43) ns was achieved, representing a 4.8x improvement over the simple dephasing time (T${2}$).
- Material Limitation Identified: The ultimate spin coherence is limited by resonant coupling to the electron spin bath formed by substitutional nitrogen impurities (P1 centers) prevalent in the HPHT diamond substrate (estimated 3.8 ppm concentration).
- Future Requirement: The paper emphasizes the necessity of utilizing ultra-pure, electronic-grade diamond substrates to suppress P1 noise and achieve the intrinsic T$_{1}$ limit of 216 ”s.
- 6CCVD Solution: 6CCVD specializes in high-purity, Electronic Grade MPCVD Single Crystal Diamond (SCD) that meets the purity requirements necessary to advance this SiV qubit research.
Technical Specifications
Section titled âTechnical SpecificationsâThe following key data points were extracted from the coherence and relaxation measurements performed at millikelvin temperatures:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Base Operating Temperature | 12 | mK | Achieved via dilution refrigerator cooling |
| Qubit Center | SiV$^{-}$ (Negatively charged Silicon-Vacancy) | N/A | Targeted color center for quantum computing |
| Applied Magnetic Field (B) | 0.21 | T | Used to lift spin degeneracy (Zeeman splitting) |
| Spin Dephasing Time (T$_{2}$) | 29(3) | ns | Measured via Ramsey interferometry at 12 mK |
| Spin Echo Coherence Time (T$_{2,echo}$) | 138(43) | ns | Measured via Hahn-echo sequence at 12 mK |
| Spin Relaxation Time (T$_{1}^{spin}$) | 108(24) | ”s | Measured at 12 mK, 300x improvement vs. 3.7 K |
| Intrinsic Coherence Limit (2T$_{1}$) | 216 | ”s | Theoretical limit in the absence of external noise sources |
| Rabi Frequency (Max Power, 80 nW) | 4.13 | MHz | Demonstrating all-optical two-photon control |
| Material Used | HPHT Type IIa bulk diamond | N/A | Sample characterized by high substitutional nitrogen concentration |
| Nitrogen Impurity Concentration (P1) | ~3.8 | ppm | Estimated average spin bath density, limiting T$_{2}$ coherence |
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized highly sophisticated cryogenic and optical techniques to achieve coherent spin control and noise analysis:
- Material and Orientation: A (111)-oriented HPHT Type IIa bulk diamond sample was used, known to contain a high concentration of substitutional nitrogen impurities (P1 centers).
- Cryogenic Confocal Setup: The sample was cooled to a base temperature of 12 mK using a dilution refrigerator equipped with free-space optical access and a high numerical aperture (NA 0.9) objective.
- Spin Level Splitting: A permanent SmCo magnet applied a 0.21 T magnetic field at an angle of 70.5° relative to the SiV symmetry axis, inducing Zeeman splitting of the S=1/2 electronic spin states.
- All-Optical Qubit Control: Ultrafast spin manipulation was performed using a bi-chromatic Raman pulse sequence, generated by a Ti:Sapphire laser combined with an Electro-Optical Modulator (EOM) and Acousto-Optical Modulators (AOMs).
- Coherence Characterization: Standard quantum sensing protocols, including Ramsey interference (for T${2}$) and Hahn-echo sequence (for T${2,echo}$), were employed to measure spin dephasing, revealing a non-Markovian noise component rephased by the Ï-pulse.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research clearly demonstrates that material purity is the primary bottleneck preventing SiV qubits from reaching their intrinsic T${1}$ coherence limit (216 ”s). The high concentration of P1 centers in the commercial Type IIa HPHT diamond severely restricts T${2}$ coherence.
6CCVD offers the Electronic Grade MPCVD Single Crystal Diamond necessary to eliminate this P1 noise floor, accelerating quantum device development.
| Research Requirement | Material/Service Solution | 6CCVD Capability & Advantage |
|---|---|---|
| Ultra-Low Impurity Substrate | Electronic Grade SCD (Single Crystal Diamond) | Our MPCVD growth process yields nitrogen concentrations significantly lower than the 3.8 ppm estimated in the paper (typically sub-ppb levels), effectively suppressing the P1 spin bath noise and enabling T$_{1}$-limited coherence. |
| Specific Crystal Orientation | Custom (111) SCD Wafers | We provide precise crystal cuts and orientations, including the required (111) surface, critical for deterministic SiV incorporation (via implantation) and optimal magnetic field alignment. |
| High Surface Quality | Optical Grade Polishing | SCD wafers are polished to Ra < 1 nm, essential for minimizing scattering losses in the confocal setup and optimizing coupling efficiency for ZPL fluorescence (737 nm) measurement. |
| Quantum Device Integration | Custom Dimensions and Thickness | We supply SCD plates/wafers up to 500 ”m thick, and can deliver thin membranes (0.1 ”m) necessary for integration into nanophotonic platforms like waveguides and photonic crystals, as referenced in QIP roadmaps. |
| Advanced Device Fabrication | Custom Metalization Services | Internal capability to deposit thin films (Au, Pt, Pd, Ti, W, Cu) for engineers designing integrated components such as microwave control lines, electrodes for Stark shift tuning, or on-chip cryo-elements. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house team of PhD material scientists are experts in quantum-grade diamond selection. We can assist engineers and researchers in defining precise specifications for MPCVD growth required to maximize SiV$^{-}$ coherence times for similar quantum information processing (QIP) and ultrafast spin manipulation projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
The silicon-vacancy center in diamond offers attractive opportunities in quantum photonics due to its favorable optical properties and optically addressable electronic spin. Here, we combine both to achieve all-optical coherent control of its spin states. We utilize this method to explore spin dephasing effects in an impurity-rich sample beyond the limit of phonon-induced decoherence: Employing Ramsey and Hahn-echo techniques at temperatures down to 40 mK we identify resonant coupling to a substitutional nitrogen spin bath as limiting decoherence source for the electron spin.