{"schema":"pubphys.bundle/1","record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"129e8dc7b35e2ee5d40920516eca303614f9fd3306559f8a1ade2e118a7eb7c9","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":["ai:gpt-5.5"],"kind":"seed"},"parents":["5c39b1cf9388247bad5d00dae3c7a8a00e169bb3c1224ae145d6910d2981dd95","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"951f81b039855c9de9b67c50a4d1650abe9bedf2405116062e7eb7419a6138d0","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"mechanism","assisted_by":["ai:gpt-5.5"],"external_id":"amo.macroscopic-optomechanics.mechanical-cat-decoherence","kind":"phenomenon","literature_status":"open","n":"2","parents":[],"plain":"A 16-microgram vibrating crystal has been put into a cat state, a superposition of two distinct motions. The question is whether its decay is fully explained by known noise, or whether something extra appears at larger mass.","posed_since":"","precise":"Mechanical resonator of effective mass $m_{\\mathrm{eff}}$ in a cat state $\\left|\\alpha\\right> + \\left|-\\alpha\\right>$. Measure the cat decoherence rate $\\Gamma_{\\mathrm{cat}}$ versus $\\mid\\alpha\\mid^2$ and $m_{\\mathrm{eff}}$, and compare with the bath model $\\Gamma_{\\mathrm{cat}} = 2 \\mid\\alpha\\mid^2 \\Gamma_{\\mathrm{m}} (2 n_{\\mathrm{th}} + 1)$, with $\\Gamma_{\\mathrm{m}}$ the mechanical energy damping rate and $n_{\\mathrm{th}}$ the thermal phonon number, plus two-level-system defect noise. Answer: whether all decoherence is accounted for, and any excess as a function of mass.","problem_ref":"5c39b1cf9388247bad5d00dae3c7a8a00e169bb3c1224ae145d6910d2981dd95","references":"","settled_by":"Systematic Wigner-function tomography of cats across masses and separations with independently measured bath parameters.","status_note":"Cat states of a 16-microgram oscillator were reported in 2023 (Bild et al., Science).","title":"What limits mechanical cat-state coherence as mass 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