Evidence for an Excited-State Efimov Trimer in a Three-Component Fermi Gas

We observe enhanced three-body recombination in a three-component ${}^6\mathrm{Li}$ Fermi gas attributable to an excited Efimov trimer state intersecting the three-atom scattering threshold near 895 G. From measurements of the recombination rate we determine the Efimov parameters ${\kappa }_{*}$ and ${\eta }_{*}$ for the universal region above 600 G which includes three overlapping Feshbach resonances. The value of ${\kappa }_{*}$ also predicts the locations of loss features previously observed near 130 and 500 G [T. B. Ottenstein et al., Phys. Rev. Lett. 101, 203202 (2008); J. H. Huckans et al., Phys. Rev. Lett. 102, 165302 (2009)] suggesting they are associated with a ground-state Efimov trimer near threshold. We also report on the realization of a degenerate three-component Fermi gas with approximate SU(3) symmetry.

Figure 1

(a) Three overlapping $s$-wave Feshbach resonances in ${}^6\mathrm{Li}$ for states $|1⟩$, $|2⟩$, and $|3⟩$ [11]. At high field, $a_{ij}\to -2140a_0$. (b) The binding energies ($E_{12}$, $E_{23}$, $E_{13}$) of the universal dimer states associated with the Feshbach resonances. The dashed lines ($n$ and $n^{\prime }$) depict the binding energies of the Efimov trimer states (not yet accurately known). Resonant three-body recombination occurs (arrows) when an Efimov trimer intersects the three-atom scattering threshold. The gray-shaded areas identify nonuniversal regions where $E<E_{\mathrm{vdW}}={\hslash }^2/m{\ell }_{\mathrm{vdW}}^2$ or $|a_{ij}|<2{\ell }_{\mathrm{vdW}}$. (For ${}^6\mathrm{Li}$, ${\ell }_{\mathrm{vdW}}=62.5a_0$.)

Figure 2

The measured three-body recombination rate constant $L_3$. Resonant three-body recombination near 900 G is caused by an excited Efimov trimer crossing the three-atom scattering threshold (see text). The inset shows typical data for $N(t)$ and $T(t)$ which are fit to extract $L_3$. In the inset the solid (dashed) line shows the fit to a model which does not include (includes) antievaporation.