{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"a3875db023ff9f175ba6c7fe37cf767c55bec25cb475714d2b26bd79d2913db0","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["3c8c7499f24150242a9bc23ab6ed431ed45c742fd87c8665341629e3ab6a55f6","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"284c26b2047520a0de6f1a30742f7961c792d6ade19bea466e31d67761dac6f4","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"qi.monitored-circuits.postselection-free-observation","kind":"well-posed","literature_status":"partially-resolved","n":"2","parents":[],"plain":"Seeing the transition directly requires repeating the same random set of measurement outcomes, which happens with exponentially small probability. A way to detect it in generic circuits with resources that grow only polynomially with size is not established.","posed_since":"","precise":"For non-Clifford monitored circuits on $N$ qubits under Born-rule measurements, find an estimator that detects $p_c$ with $\\operatorname{poly}(N)$ samples and $\\operatorname{poly}(N)$ classical processing, or prove that every such probe needs $\\exp(N)$ resources. Known probes use Clifford circuits, require classically simulating the circuit (cross-entropy benchmark of Li, Zou, Glorioso, Altman and Fisher, PRL 130, 220404, 2023), or postselect.","problem_ref":"3c8c7499f24150242a9bc23ab6ed431ed45c742fd87c8665341629e3ab6a55f6","references":"","settled_by":"An efficient detection protocol with proof and a demonstration on hardware, or a lower bound on sample complexity.","status_note":"Google Quantum AI (Nature 2023) observed measurement-induced entanglement signatures on a processor of about 70 qubits (approximate) using decoding methods; the general question is open.","title":"Observing the measurement-induced transition without exponential 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