Feshbach resonance: a(B) = a_bg(1 − Δ/(B − B_0)) — tunable interactions

Feshbach 1958 (nuclear scattering); Tiesinga-Verhaar-Stoof 1993 (ultracold atoms); Inouye et al 1998 (observation in ²³Na condensate). When the energy of a molecular bound state in a closed channel crosses the scattering threshold of an…