{"record":{"author":{"account_ref":null,"orcid":null},"builds_on":[],"content_schema":"pubphys.content.revision/1","content_sha256":"a0ce9c7d71d350b265e62b67ef79218926729a497bb809302aac298961696fe3","created":"2026-10-15T23:43:22Z","files":[],"origin":{"assisted_by":[],"kind":"seed"},"parents":["a03adf8929526af28c3ccb8aebc93561e72f4fe6a087b541161396b3e506dec2","ce59fb6cd812fc05906d0c60a71c75ea22bc686bcf38e7c3ef7010834d98ee7b"],"salt":"745f8e5a7786daf45715322f1960b29ffc512c93c4099f54861a128e50994572","schema":"pubphys.record/2","site":"pubphys.com","target":null,"type":"revision"},"content":{"answer_type":"identification","assisted_by":[],"external_id":"beams.srf-cavities.residual-resistance-floor","kind":"well-posed","literature_status":"open","n":"2","parents":[],"plain":"Even far below the superconducting transition, cavities keep a small leftover energy loss whose sources are only partly identified.","posed_since":"","precise":"At $T <\\sim 1.5\\,\\mathrm{K}$, where the BCS surface resistance at 1.3 GHz is negligible, the quality factor of the best Nb cavities saturates at $Q_0$ of order $10^{11}$ (residual resistance $\\sim 1-3\\,\\mathrm{nOhm}$), set by a temperature-independent residual surface resistance. Determine the fractions contributed by trapped magnetic vortices, two-level systems in the surface $\\mathrm{Nb_2O_5}$ oxide, and subgap quasiparticle states, as functions of field, frequency and surface treatment.","problem_ref":"a03adf8929526af28c3ccb8aebc93561e72f4fe6a087b541161396b3e506dec2","references":"","settled_by":"Measurements of residual resistance versus trapped flux, frequency and field, combined with oxide removal or regrowth, that separate the three contributions.","status_note":"","title":"What sets the residual surface resistance floor of niobium cavities?","topic_ref":null},"attested":{"attestation":{"batch":null,"client_id":null,"id_token_sha256":null,"kind":"platform"},"record_hash":"e7b37b042911891c2d57b1be6f1038aff04636f820138fdf9d4fb2ee287ba223","schema":"pubphys.attested/1"},"envelope":{"attested_hash":"bd1500589ba2caa4cbbcdb84383916cd2f0efcda2558aca27bd0d6bdf2fd5b76","platform_signature":{"key_id":"c6afc19b31429869751f06879c75cd64ea92654423d15b44be775bf1310a60da","sig":"2nmdGLIook0Gw8cMf41KJSrwXTAh4aBNBf89u2kZAeV7FSY3x9XAR9UZtNHgbQBQgp1661yr3G9Sj8ZDAdhNCA"},"schema":"pubphys.envelope/1"},"record_hash":"e7b37b042911891c2d57b1be6f1038aff04636f820138fdf9d4fb2ee287ba223","leaf_index":2540}