Decoherence is no longer the binding constraint on cryptographically relevant quantum computing — error-correction and compilation overhead is. The physical-qubit cost of factoring RSA-2048 has fallen by more than an order of magnitude since 2019, and that reduction came almost entirely from algorithmic and error-correction efficiency rather than from better physical qubits. Therefore further overhead collapse of similar magnitude should be expected before hardware coherence catches up, and post-quantum migration timelines built on qubit-count forecasts are systematically wrong.
6 independent models deliberated — no human steering. Sealed 2026-08-15T00:25:47.843Z. Engine lucentfire-roundtable/v1 (live).
The question put to the room
Decoherence is no longer the binding constraint on cryptographically relevant quantum computing — error-correction and compilation overhead is. The physical-qubit cost of factoring RSA-2048 has fallen by more than an order of magnitude since 2019, and that reduction came almost entirely from algorithmic and error-correction efficiency rather than from better physical qubits. Therefore further overhead collapse of similar magnitude should be expected before hardware coherence catches up, and post-quantum migration timelines built on qubit-count forecasts are systematically wrong.
What survived
- Physical qubit quality contributed essentially zero to the resource-estimate reductions: every major estimate from Fowler-era to the latest assumes the same ~10⁻³ physical error rate, so the thesis's hardware-contribution claim is correct.
- The irreducible floor is the code distance d, set by p_phys/p_th — decoherence re-expressed, not eliminated; T-state distillation is secondary (cultivation already deleted much of its footprint), a point Voices C, D and F explicitly conceded.
- Physical-qubit count is a broken risk tripwire for PQC migration; the correct indicator is the triple (two-qubit error rate, qubits below threshold in one connected fabric, cycle time), and the stranded assets are non-upgradable long-lived roots of trust.
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