Magneto-association near an atom-dimer resonance

Over the past decade the universal scaling of Efimov trimers has been explored in various atomic species by measuring the three-body loss coefficient. An enhancement of the three-body loss at the atom-dimer resonance has been observed,\footnote{S.E. Pollack, D. Dries, \& R.G. Hulet, Science, 326, 1683 (2009) }$^{,}$\footnote{M. Zaccanti et al. Nature Physics, 5, 586 (2009)} but remains unexplained. It has been attributed to an ``avanlanche mechanism'' based on resonant atom-dimer scattering, yet the effectiveness of the hypothesis is under scrutiny.\footnote{J. Schuster et al. Phys. Rev. Lett. 87, 170404 (2001) }$^{,}$\footnote{M. Hu et al. Phys. Rev. A 90, 013619 (2014)} We present a new piece to the puzzle. In our work, Feshbach dimers and Efimov trimers are formed near the atom-dimer resonance by RF-association, from a Bose-Einstein condensate of $^7$Li atoms. The molecular binding energies are tunable by the broad Feshbach resonance of the atoms in the $|1,1\rangle$ state. We observe that the dimer formation rate is significantly enhanced at the atom-dimer resonance. The origin of this enhanement is unclear, but it may be closely related to the enhancement of the three-body loss rate.