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 2026-08-15T00:05:55.127Z. 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
- The physical-qubit requirement for factoring RSA-2048 has fallen by more than an order of magnitude since the ~20 million-qubit 2019 estimate, with current credible work placing it below one million physical qubits under similar error-rate assumptions.
- That qubit-cost reduction is driven primarily by algorithmic, compilation, and error-correction innovations (approximate arithmetic, yoked surface codes, improved magic-state handling), not by major improvements in physical-qubit coherence or gate error rates.
- Post-quantum migration strategies that treat very high qubit-count thresholds (10^7–10^9 qubits) as a robust safety margin are structurally fragile, because software and architectural overhead can and demonstrably does collapse faster than hardware coherence improves.
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