Silicon-Carbide Defect Qubit

Figure

Description

Silicon-carbide defect qubits use optically addressable electron spins associated with point defects in a technologically mature wide-band-gap semiconductor. Two major branches must not be conflated: the neutral divacancy has an $S=1$ ground state analogous in control language to diamond NV centers, while the negatively charged silicon vacancy has an $S=3/2$ ground state and different level structure.

SiC combines optical initialization/readout, microwave spin control, nearby nuclear-spin registers, and wafer-scale growth and nanofabrication. Its near-infrared optical transitions are attractive for spin-photon interfaces, though spectral stability and photon collection remain less mature than the best diamond nanophotonics.

Hamiltonian

For an axial neutral divacancy, a useful ground-state spin Hamiltonian is

$H=D\left(S_z^2-\frac{S(S+1)}{3}\right)+E(S_x^2-S_y^2)+g{\mu }_B\mathbf{B}\cdot \mathbf{S}+\mathbf{S}\cdot \mathbf{A}\cdot \mathbf{I},$

with $S=1$, zero-field splitting $D$, transverse strain/electric-field parameter $E$, and hyperfine tensor $\mathbf{A}$. Both $D$ and the sign and magnitude of the optical spin contrast depend on polytype, lattice site, and defect configuration, so values such as $D/2\pi \approx 1.34$ GHz apply to a specified center (for example PL6), not to every SiC divacancy. Silicon-vacancy centers require an $S=3/2$ crystal-field Hamiltonian; they are a related defect branch, not the same qubit.

Motivation

• Retain optically addressable defect-spin physics in a semiconductor with established wafer processing.
• Integrate spin memories with nanophotonic cavities and electrical devices on the same material platform.
• Exploit multiple defect species and nuclear-spin registers while maintaining a clear physical taxonomy.

Experimental Status

Room-temperature coherent control of SiC defect spins was demonstrated in 2011. Christle et al. isolated and coherently controlled individual neutral divacancies and measured ensemble Hahn-echo coherence exceeding 1 ms. Nagy et al. demonstrated high-fidelity spin and optical control of single silicon-vacancy centers in 4H-SiC.

The platform has since advanced from isolated-spin control to network-node primitives. Bourassa et al. entangled a divacancy electron spin with a single ${}^{29}$Si nuclear spin while reporting 99.984(1)% electron-spin control fidelity and $T_2^{\mathrm{DD}}>14.5$ ms. Fang et al. generated V1 silicon-vacancy spin–photon entanglement with fidelity $75.7\pm 1.5$%. In 2024, Hu et al. prepared an ambient-condition PL6 electron–${}^{13}$C Bell state with fidelity 0.89 and retained 0.88 after integration into a silicon-carbide-on-insulator waveguide. Nishikawa et al. then demonstrated coherent room-temperature photoelectrical readout of an individual V2 silicon-vacancy spin with 1.7–2 times the signal-to-noise ratio of their optical readout. Morioka et al. broadened the electrical-readout picture in 2026 by demonstrating coherent photoelectrical detection and spectroscopy of PL3 and PL5–PL7 ensembles.

Key Metrics

Metric	Value	Notes	Fidelity reference
Hahn-echo $T_2$	>1 ms	Neutral divacancy ensemble in high-purity 4H-SiC	Christle et al. 2015
Electron-spin control	99.984(1)%	Isotopically engineered divacancy; randomized benchmarking	Bourassa et al. 2020
Dynamically decoupled $T_2$	>14.5 ms	Isotopically engineered divacancy; Hahn echo $T_2=2.3$ ms	Bourassa et al. 2020
Spin–photon entanglement fidelity	$75.7\pm 1.5$%	V1 silicon vacancy, time-bin photonic qubit	Fang et al. 2024
Electron–nuclear Bell-state fidelity	0.89 (0.88 after waveguide integration)	PL6 divacancy–${}^{13}$C register at ambient conditions	Hu et al. 2024
Operating regime	Room temperature demonstrated	Coherent defect-spin control	Koehl et al. 2011
Single-spin photoelectrical readout	1.7–2× optical-readout SNR	Individual V2 silicon vacancy at room temperature	Nishikawa et al. 2025
Photoelectrical readout	Room-temperature coherent PDMR	PL3 and PL5–PL7 defects	Morioka et al. 2026
Defect branches	$S=1$ and $S=3/2$	Divacancy and silicon-vacancy encodings	Nagy et al. 2019

Scaling Considerations

• Different polytypes, lattice sites, and charge states create a rich but fragmented device landscape.
• Transform-limited optical lines and stable charge-state control are required for remote entanglement.
• Isotopic purification and nuclear-spin engineering can extend coherence but add materials complexity.
• Foundry compatibility is promising, but reproducible cavity-coupled single-defect yield remains a bottleneck.
• Photoelectrical magnetic-resonance readout offers a path around inefficient near-infrared photon collection, but defect-dependent ionization and electrical contrast still require device-level optimization.

References

• W. F. Koehl et al., “Room temperature coherent control of defect spin qubits in silicon carbide,” Nature 479, 84–87 (2011).
• D. J. Christle et al., “Isolated electron spins in silicon carbide with millisecond coherence times,” Nature Materials 14, 160–163 (2015).
• R. Nagy et al., “High-fidelity spin and optical control of single silicon-vacancy centres in silicon carbide,” Nature Communications 10, 1954 (2019).
• A. Bourassa et al., “Entanglement and control of single nuclear spins in isotopically engineered silicon carbide,” Nature Materials 19, 1319–1325 (2020); arXiv:2005.07602.
• R.-Z. Fang et al., “Experimental Generation of Spin-Photon Entanglement in Silicon Carbide,” Physical Review Letters 132, 160801 (2024); arXiv:2311.17455.
• H. Hu et al., “Room-temperature waveguide integrated quantum register in a semiconductor photonic platform,” Nature Communications 15, 10256 (2024).
• T. Nishikawa et al., “Coherent photoelectrical readout of single spins in silicon carbide at room temperature,” Nature Communications 16, 3405 (2025).
• N. Morioka et al., “Photoelectrical detection and characterization of divacancy and PL5–PL7 spins in silicon carbide,” Physical Review B 113, 104426 (2026); arXiv:2512.05283.

Linked Papers

• koehl-2011-sic-defect-spin-control
• christle-2015-sic-divacancy
• nagy-2019-sic-silicon-vacancy
• bourassa-2020-sic-nuclear-spin-register
• fang-2024-sic-spin-photon-entanglement
• hu-2024-sic-waveguide-quantum-register
• nishikawa-2025-sic-single-spin-photoelectrical-readout
• morioka-2026-sic-photoelectrical-readout

Evergreen context

• coherence-time-hierarchy — connects electron-spin operations to longer nuclear-memory timescales.
• divincenzo-criteria — evaluates the trade between local spin quality and network-interface maturity.

Related Entries

• nv-center-qubit — diamond defect-spin baseline.
• siv-color-center-qubit — group-IV diamond defects optimized for optical quality.
• t-center-qubit — telecom-adjacent silicon defect node.
• quantum-transduction — frequency conversion for linking near-infrared SiC emitters to telecom networks.
• qubit-readout — optical and emerging photoelectrical spin-readout methods.