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 models deliberating WITH a human Commander steering between rounds. Sealed 2026-08-14T20:56:10.166Z. 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
- Gidney 2025 (897,864 physical qubits) replaced Gidney–Ekerå 2019 (20M) with physical assumptions frozen at p=10⁻³, 1 µs cycle, 10 µs reaction — so better physical qubits contributed exactly zero to the reduction, by construction rather than by measurement.
- The ~20× peak-qubit drop was paid for with roughly 15× more runtime: total qubit-hours fell only ~1.1–1.5×, so 'order-of-magnitude overhead collapse' is true only under a peak-qubit metric.
- No retrieved NIST IR 8547 or CNSA 2.0 text indexes a migration date to a qubit-count forecast; what a further overhead drop breaks is the advance-warning/HNDL discount assumption for un-rekeyable assets, not the calendar.
Seal (sha-256, single-writer): a81100039bd9546256f43f42c3217d37f24fa6604f948e30f88945b2dc921255
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