Atom-Dimer Scattering in a Three-Component Fermi Gas

Ultracold gases of three distinguishable particles with large scattering lengths are expected to show rich few-body physics related to the Efimov effect. We have created three different mixtures of ultracold ${}^6\mathrm{Li}$ atoms and weakly bound ${}^6\mathrm{Li}_2$ dimers consisting of atoms in three different hyperfine states and studied their inelastic decay via atom-dimer collisions. We have found resonant enhancement of the decay due to the crossing of Efimov-like trimer states with the atom-dimer continuum in one mixture as well as minima of the decay in another mixture, which we interpret as a suppression of exchange reactions of the type $|12⟩+|3⟩\to |23⟩+|1⟩$. Such a suppression is caused by interference between different decay paths and demonstrates the possibility of using Efimov physics to control the rate constants for molecular exchange reactions in the ultracold regime.

Figure 1

(a) Magnetic field dependence of the two-body $s$-wave scattering lengths for different channels in units of Bohr radius $a_0$ [30]. (b) Binding energies of the universal dimer and trimer states according to 19. The vertical lines mark the predicted crossings of the trimer states with the $|1⟩\mathrm{\text{−}}|23⟩$ atom-dimer threshold. The red diamonds mark the positions of the resonant enhancement observed in ${\beta }_{1\mathrm{\text{−}}23}$ and the black squares mark the interference minima in ${\beta }_{3\mathrm{\text{−}}12}$.

Figure 2

Two-body loss rate for a mixture of state $|1⟩$ atoms and $|23⟩$ dimers versus magnetic field. The line is a fit according to Eq. (3); the solid part of the line marks the magnetic field range included in the fit.

Figure 3

Measured two-body loss rate for the $|3⟩\mathrm{\text{−}}|12⟩$ and $|2⟩\mathrm{\text{−}}|13⟩$ atom-dimer mixtures versus magnetic field.