Physics / mechanism
Silicon spin qubits encode quantum information in the spin state (↑/↓) of single electrons or holes confined in gate-defined quantum dots fabricated on silicon or Si/SiGe heterostructures. Confinement is electrostatic; qubit control uses microwave pulses via exchange coupling or electron dipole spin resonance (EDSR). Key parameters: T2* coherence ~1–100 µs (isotopically purified ²⁸Si pushes toward the upper bound), single-qubit gate fidelities >99.9% demonstrated at single-dot level, two-qubit fidelities 96–99% in best academic results. Intel’s Horse Ridge cryogenic controller + Tunnel Falls 12-qubit chip and Quantum Motion’s CMOS-native foundry approach represent the industrial frontier. Operating temperature: 50–300 mK (some demonstrations at 1K). Qubit density potential is high; dot pitch ~50 nm is compatible with existing fab nodes.
Competitive landscape
Competing modalities: superconducting transmons (Google, IBM) have faster gates (~10–100 ns) but lower T2 and require dilution temps; trapped ions offer >99.9% two-qubit fidelity but poor scalability density; photonic qubits (PsiQuantum) sidestep coherence but demand extreme loss specs. Within solid-state spin: NV centers in diamond offer room-temp operation but poor uniformity; germanium spin qubits (Delft) show higher hole mobility and easier spin-orbit control.
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Frontier (open questions)
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