Polytype control of spin qubits in silicon carbide

Abstract: Crystal defects can confine isolated electronic spins and are promising candidates for solid-state quantum information. Alongside research focusing on nitrogen vacancy centers in diamond, an alternative strategy seeks to identify new spin systems with an expanded set of technological capabilities, a materials driven approach that could ultimately lead to "designer" spins with tailored properties. Here, we show that the 4H, 6H and 3C polytypes of SiC all host coherent and optically addressable defect spin states, including spins in all three with room-temperature quantum coherence. The prevalence of this spin coherence shows that crystal polymorphism can be a degree of freedom for engineering spin qubits. Long spin coherence times allow us to use double electron-electron resonance to measure magnetic dipole interactions between spin ensembles in inequivalent lattice sites of the same crystal. Together with the distinct optical and spin transition energies of such inequivalent spins, these interactions provide a route to dipole-coupled networks of separately addressable spins.

• The paper demonstrates that defect spin qubits in various SiC polytypes exhibit coherent and optically addressable states with spin polarizations up to 60%.
• The authors use ODMR and pulsed magnetic resonance sequences such as Rabi, Ramsey, and Hahn-echo to reveal coherence times up to 360 μs at cryogenic temperatures and around 50 μs at room temperature.
• The research underscores silicon carbide’s polytypism as a versatile tool for engineering scalable quantum systems through controlled defect patterning and precise ion implantation techniques.

Overview of Polytype Control of Spin Qubits in Silicon Carbide

The paper "Polytype Control of Spin Qubits in Silicon Carbide" presents an exploration of silicon carbide (SiC) polytypes as a promising platform for solid-state quantum information systems. The research investigates the coherent and optically addressable defect spin states in the 4H, 6H, and 3C polytypes of SiC, highlighting their potential for room-temperature quantum coherence. This examination offers evidence that SiC's crystal polymorphism can serve as a versatile parameter for engineering tailored spin qubits.

Coherent Spin States Across SiC Polytypes

The study sets out to identify new defect-based spin systems capable of providing desirable characteristics for quantum technology applications. Through optically detected magnetic resonance (ODMR) measurements, the authors demonstrate that all three examined polytypes possess coherent spin states. These spin states are found in neutral divacancies and similar defects, retaining coherence at ambient temperatures, which is crucial for practical quantum computing applications. Notably, the research identifies high optical spin polarizations, pivotal for efficient spin control, ranging between 35% to 60% depending on the defect species.

Spin Coherence and Defect Engineering

Through advanced pulsed magnetic resonance techniques, including Rabi, Ramsey, and Hahn-echo sequences, the authors detail the long coherence times achieved across the different SiC polytypes. At cryogenic temperatures, spin relaxation times span from 8 to 24 ms, with Hahn-echo coherence times reaching up to 360 μs, depending on the sample's attributes. Importantly, certain defects maintain coherent spin states at room temperature, such as neutral divacancies in 4H-SiC, exhibiting coherence times around 50 μs.

Spin Interactions and Technological Implications

The research explores magnetic dipole-dipole interactions between spin ensembles at inequivalent lattice sites, utilizing double electron-electron resonance (DEER) techniques. This interaction knowledge is essential for devising coupled spin networks, a fundamental requirement in quantum technologies. The capability to pattern spin ensembles further enables the spatial engineering of spin qubits, providing a pathway towards scalable spin-based quantum systems.

Silicon carbide's polymorphic nature provides a unique feature not available in diamonds, the current frontrunner material for hosts of spin qubits. This polymorphism facilitates the creation of hybrid quantum systems incorporating mechanical and photonic elements, given 3C-SiC's compatibility as an epitaxial film on silicon substrates.

Considerations and Future Prospects

The experimental approach involves comprehensive ion implantation and annealing strategies to control defect concentrations effectively. Patterning through ion implantation techniques demonstrates the feasibility of spatial organization of defect sites within SiC. The prospect of further developing these techniques could leverage established semiconductor manufacturing processes to integrate defect spins into larger optoelectronic platforms.

The findings from this paper suggest that silicon carbide, through its polytype variability, offers an innovative and versatile playground for solid-state quantum information science. Further explorations that refine the control over defect creation and addressability could propel SiC to the forefront as a quantum information material, complementing and potentially surpassing current technologies in certain applications. The advancement of coherent spin control within SiC holds promising potential for expanding the capabilities and integration of quantum information systems.