{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"0ade184a0a8309f199f91e422b0a8d1892dac0ab17438f11baed88e511416742","created":"2026-10-03T07:17:54Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["5475cf5dc5b1a72283d26dc95dc6e00d7ea4e00096a7c6492e409a1816eeb011"],"salt":"9fbbec9d742d2c22ffe0ec20748ce201a099d33d66f0c8e2cdeb617521bfa002","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"value","assisted_by":[],"external_id":"amo.unitary-fermi-transport.viscosity-entropy-minimum","kind":"well-posed","literature_status":"open","n":"1","parents":[],"plain":"Viscosity divided by entropy measures how close a fluid comes to flowing with no internal friction. A conjectured lower limit is 1/(4 pi) in natural units, and the unitary gas is among the closest fluids to it.","posed_since":"","precise":"Homogeneous unitary Fermi gas ($1/a = 0$). Measure $\\eta/s$ as a function of $T/T_F$ through $T_c = 0.167\\,T_F$, in units of $\\hbar/k_B$, and locate its minimum. Answer: minimum value and position with 10% uncertainty, including the two-fluid regime below $T_c$.","problem_ref":null,"references":"","settled_by":"Uniform-box measurements of viscous damping with local entropy thermometry, or a controlled Kubo-formula calculation that matches them.","status_note":"Trap-averaged measurements up to 2015 placed the minimum at roughly 0.4 to 0.5 $\\hbar/k_B$ near $T_c$, several times $1/(4\\pi)$; a 2020 uniform-box measurement found sound diffusivity of order $\\hbar/m$ near $T_c$ (Patel et al., Science 2020), but a homogeneous $\\eta/s(T)$ curve through $T_c$ is lacking.","title":"Minimum shear viscosity to entropy ratio of the unitary 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