{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"5e0a692fe09e5c23e7c4b3d27ece3db22744dceb4974164e5245cdacf3a80199","created":"2026-10-03T07:18:10Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"84008892507b9379574d8b11a180da8be85cd1dbc2add2f37491b6c3ae275e17","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":"1","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 $\\operatorname{exp}(N)$ 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":null,"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 postselection","topic_ref":"da5948613fb7c747a01db9b5effa765ea41c69dc5d5e33ffbeb4df2a77c0fb36"},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"3c8c7499f24150242a9bc23ab6ed431ed45c742fd87c8665341629e3ab6a55f6","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"f9eb4d85dd6829609a7762b9791ac05f938c3a1ac91c26d31c02f3846bafe2eb","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"7spAO05s6ZtioFak7PgiqCgDrRUYVZ3xfETVHiPTI6ZaOsgCrmjxe8ZRpHj12icbnAyHyTyU6GYZogcptZaYAg"},"schema":"pubphys.envelope/1"},"record_hash":"3c8c7499f24150242a9bc23ab6ed431ed45c742fd87c8665341629e3ab6a55f6","leaf_index":2022}