High-fidelity spin and optical control of single silicon vacancy centres in silicon carbide (1810.10296v1)

Abstract: Optically interfaced spins in the solid promise scalable quantum networks. Robust and reliable optical properties have so far been restricted to systems with inversion symmetry. Here, we release this stringent constraint by demonstrating outstanding optical and spin properties of single silicon vacancy centres in silicon carbide. Despite the lack of inversion symmetry, the system's particular wave function symmetry decouples its optical properties from magnetic and electric fields, as well as from local strain. This provides a high-fidelity spin-to-photon interface with exceptionally stable and narrow optical transitions, low inhomogeneous broadening, and a large fraction of resonantly emitted photons. Further, the weak spin-phonon coupling results in electron spin coherence times comparable with nitrogen-vacancy centres in diamond. This allows us to demonstrate coherent hyperfine coupling to single nuclear spins, which can be exploited as qubit memories. Our findings promise quantum network applications using integrated semiconductor-based spin-to-photon interfaces.

• The paper achieves high-fidelity optical and spin control of single silicon vacancy centers, enabling stable photon emissions with near-transform-limited 60 MHz linewidth.
• The study employs electron irradiation and confocal microscopy on isotopically purified 4H-SiC, yielding spin coherence times around 20.85 ms.
• The significant hyperfine coupling and spectral stability broaden the potential of non-inversion symmetric systems for scalable quantum communication and computing.

High-Fidelity Spin and Optical Control of Single Silicon Vacancy Centres in Silicon Carbide

The paper under discussion presents significant advancements in quantum information science using silicon carbide (SiC) as a host material for single silicon vacancy centers. This work addresses a primary challenge in developing quantum networks: the scalability of optically interfaced spins in solid-state environments. Historically, systems with inversion symmetry have been favored for their robust optical properties. However, this paper demonstrates that inversion symmetry is not a necessary condition, expanding the potential material candidates for quantum applications.

Key Findings:

1. Optical Properties and Stability: The paper details the discovery that single silicon vacancy centers in SiC offer exceptionally stable and narrow optical transitions with low inhomogeneous broadening. The optical properties are decoupled from external magnetic, electric fields, and local strain due to unique wavefunction symmetry. This decoupling results in high-fidelity spin-to-photon interfaces with a significant fraction of resonantly emitted photons.
2. Spin Coherence: The weak spin-phonon coupling in the silicon vacancy centers leads to spin coherence times comparable to nitrogen-vacancy (NV) centers in diamond. The coherence times in 4H-SiC are measured to be around 20.85 ms, making it a promising candidate for quantum computing and memory applications.
3. Hyperfine Coupling: The researchers demonstrate coherent hyperfine coupling to single nuclear spins, which are critical for developing qubit memories. The substantial hyperfine interaction enables potential integration into quantum networks and quantum memory applications.
4. Experimental Methodology: Utilizing a 4H polytype of SiC, the paper involved creating silicon vacancies by electron irradiation in isotopically purified layers of SiC, followed by optical and electron spin studies. Techniques like confocal microscopy facilitated the high-resolution examination at cryogenic temperatures.
5. Spectral Stability: The findings highlight that due to the intrinsic symmetry of the SiC defects, these centers show negligible sensitivity to strain and stray charges. A considerable experimental result was the nearly transform-limited linewidth of 60 MHz, approaching theoretical limits.

Implications and Future Directions:

This research has profound implications for the field of quantum information technology. By demonstrating that non-inversion symmetric systems can also possess desirable stability and coherence properties, a broader class of materials becomes available for future quantum technologies.

1. Applications in Quantum Networks: The favorable optical transition wavelength near 861 nm aligns well with existing telecom technologies, suggesting possible integration with fiber-optic networks for long-distance quantum communication.
2. Scalability: The potential for high-fidelity spin-photon entanglement and fast optical spin manipulation suggests that silicon vacancy centers in SiC can serve as scalable quantum bits in integrated semiconductor devices, advancing quantum computation and simulation.
3. Material Engineering: Future work could focus on optimizing the sample preparation, especially in mitigating defects introduced during processing, to further enhance coherence times beyond current values.

In summary, this paper contributes significantly to the understanding and application of silicon vacancy centers in silicon carbide, paving the way for novel quantum technologies. The reduction in reliance on systems with strict symmetry requirements could revolutionize the design and implementation of future quantum networks, emphasizing scalability, efficiency, and integration with current communication infrastructures. Future research could unravel even more potential of SiC and similar materials in quantum computing and sensing applications.