{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"6cff69ea6ea1b3437d27044cd2f818dd1833b8af3e6bf825c0cf8bb930bb32df","created":"2026-10-03T07:18:09Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"ce38f636494fce047f7657213ca0cfacc53477cda60b138002a385ebd6e0e0ae","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"yes-no","assisted_by":[],"external_id":"qi.contextuality-nonlocality.werner-povm-locality","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"Measurements can be generalized beyond simple projections by using helper systems. For Werner states it is unknown whether such generalized measurements reveal nonlocality at higher noise than projective ones.","posed_since":"2002","precise":"Let $v_c^{\\mathrm{POVM}}$ be the critical visibility of $\\rho_W(v)$ under arbitrary local POVMs. Known: rho_W(v) is local for all POVMs when $v \\le 1/2$ (Zhang and Chitambar, arXiv:2309.09960) and for projective measurements when $v \\le 0.6875$. Determine whether $v_c^{\\mathrm{POVM}}$ equals the projective threshold $v_c$.","problem_ref":null,"references":"","settled_by":"A local model for all POVMs up to the projective threshold, or a POVM Bell inequality violated below it.","status_note":"The analogous steering question was settled in 2023: POVMs give no advantage and the threshold is $v = 1/2$ (arXiv:2309.09960).","title":"Do general measurements beat projective ones for Werner-state 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