{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"2258ea1932f108d2f925e32a914d4226cf09b7442efe257f5668fd0bf10f6a81","created":"2026-10-03T07:18:09Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"b00c7064160625854ab3f140dbaafc00a29844c07ca036c87602507edb654716","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"qi.classical-simulability.nonunital-noise-sampling","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"Noise that scrambles qubits toward randomness makes deep quantum circuits easy to imitate classically. Noise that pushes qubits toward a fixed state, as energy loss does, behaves differently, and whether such noisy circuits can be imitated is open.","posed_since":"","precise":"For random geometrically local circuits on $n$ qubits (Haar two-qubit gates, brickwork, depth $D$) with single-qubit amplitude damping of strength $\\gamma > 0$ after each gate and no mid-circuit measurement, is there a $\\operatorname{poly}(n, 1/\\delta)$ classical algorithm that samples the output to total-variation error $\\delta$ for all $D \\ge D_0(\\gamma)$, with $D_0$ independent of $n$? Local expectation values are classically computable because this noise limits the effective depth to $O(\\log n)$ (Mele et al. 2024), but outputs do not anticoncentrate (Fefferman et al. 2024), so existing sampling arguments fail; for unital depolarizing noise of strength $p$, a 2026 preprint proves efficient sampling for $D \\ge \\Omega(p^{-1} \\log p^{-1})$ in any geometrically local circuit (arXiv:2610.00548).","problem_ref":null,"references":"","settled_by":"An efficient sampling algorithm with proof for the non-unital model above a noise-set depth, or a hardness argument for some depth regime growing with n.","status_note":"","title":"Classical sampling of random circuits with non-unital 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