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 2026-08-15T00:05:35.116Z. 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 error-rate assumptions were held essentially fixed (~10⁻³ surface-code) across the 2019 and post-2019 resource estimates, so the reduction is genuinely non-hardware in origin — this is the thesis's strongest and least contested plank.
- There is a hard floor set by the logical spacetime volume of modular exponentiation / non-Clifford count; compilation cleverness cannot go below it (all voices agree a floor exists, though they locate it differently: arithmetic gate complexity vs. magic-state distillation cost vs. logical-qubits × code-distance product).
- The practically binding failure in migration planning is data shelf-life and long-lived roots of trust (HNDL, 20-year certificates, firmware signing), not the qubit-count threshold itself — near-unanimous across seats.
Seal (sha-256, single-writer): 4b84febb04a7eb330a3ee774819aa31fad78281dd3bc476186b8b2018d155e7d
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