Emergent inflation of the Efimov spectrum under three-body spin-exchange interactions

One of the most fascinating predictions of few-body quantum physics is the Efimov effect, a universal accumulation of an infinite geometric series of three-body bound states at a two-body scattering resonance. Ever since the first experimental observation of such an Efimov state, the precise characterization of their physical properties has continued to challenge few-body theory. This is demonstrated most strongly by the lithium few-body puzzle, a remarkable theoretical discrepancy with the observed Efimov spectrum in 7Li. Here, we resolve this long-standing puzzle, demonstrating that the discrepancy arises out of the presence of strong non-universal three-body spin-exchange interactions. This conclusion is obtained from a thorough numerical solution of the quantum mechanical three-body problem, including precise interatomic interactions and all spin degrees of freedom for three alkali-metal atoms. Our results show excellent agreement with the experimental data regarding both the Efimov spectrum and the absolute rate constants of three-body recombination, and in addition reveal a general product propensity for such triatomic reactions in the Paschen-Back regime, stemming from Wigner's spin conservation rule.