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Research dossier · version 1 · updated Oct 30, 2026

Photonic, Spin & Topological Qubits: State of the Field (October 2026)

An expert briefing, current to late October 2026, on three qubit families outside the superconducting and trapped-atom mainstream: photonic qubits built from fusion-based and continuous-variable/GKP architectures, semiconductor spin qubits in silicon and germanium, and Majorana-based topological qubits. Silicon-photonic platforms report component fidelities above 99% when photon detection is conditioned on, and the platform's authors identify optical loss as the main remaining gap. Silicon spin qubits have reached about 99% single-qubit control fidelity in research devices, and 2026 work centres on control electronics and shuttling. Majorana tetron preprints report parity lifetimes from microseconds to about 20 seconds, but whether these devices host topological zero modes remains contested.

4,876 words42 sources26 evidence-mapped claims21 benchmarks16 timeline events✓ citation-verified Oct 30, 2026

AI-assisted synthesis of the cited literature, independently fact-checked against its sources; not peer reviewed.

Contents

  1. Executive summary
  2. Background and core concepts
  3. Timeline of key milestones
  4. State of the art
  5. Photonic qubits: fusion-based architectures
  6. Continuous-variable photonics and GKP
  7. Silicon and germanium spin qubits
  8. Majorana-based topological qubits
  9. Quantitative benchmarks
  10. Open problems and active debates
  11. Major programs and players
  12. Outlook: what to watch (next 12-18 months)
  13. Key papers
  14. Glossary

Sample findings

  • A 2025 silicon-photonics platform reports dual-rail state preparation and measurement at 99.98% ± 0.01%, conditional on photon detection and excluding loss.
  • The same platform reports Hong–Ou–Mandel visibility of 99.50% ± 0.25%, two-qubit fusion fidelity of 99.22% ± 0.12% and chip-to-chip interconnect fidelity of 99.72% ± 0.04%, and the abstract states that these figures are conditional on photon detection and do not include loss.
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