Collisional Stability of ${}^{40}\mathbf{K}$ Immersed in a Strongly Interacting Fermi Gas of ${}^6\mathrm{Li}$

We investigate the collisional stability of a sample of ${}^{40}\mathrm{K}$ atoms immersed in a tunable spin mixture of ${}^6\mathrm{Li}$ atoms. In this three-component Fermi-Fermi mixture, we find very low loss rates in a wide range of interactions as long as molecule formation of ${}^6\mathrm{Li}$ is avoided. The stable fermionic mixture with two resonantly interacting spin states of one species together with another species is a promising system for a broad variety of phenomena in few- and many-body quantum physics.

Figure 1

Remaining number of ${}^6\mathrm{Li}$ atoms per spin state (open squares) and of ${}^{40}\mathrm{K}$ atoms (filled circles) after a hold time of 1 s at a variable magnetic field. The dashed line at 834 G marks the center of the broad ${}^6\mathrm{Li}$ Feshbach resonance and the dotted lines at 765 and 990 G indicate the strongly interacting regime, where $|k_F^{\mathrm{Li}}a|\ge 1$. The error bars indicate the statistical error of ten measurements.

Figure 2

${}^6\mathrm{Li}$ (open squares) and ${}^{40}\mathrm{K}$ (filled circles) atom number normalized to the respective initial atom number over hold time for 665 and 834 G.

Figure 3

Upper bounds ${\mathcal{L}}_2$ and ${\mathcal{L}}_3$ (circles and triangles, respectively) for the two- and three-body loss rate coefficients of ${}^{40}\mathrm{K}$ immersed in a strongly interacting degenerate ${}^6\mathrm{Li}$ sample throughout the ${}^6\mathrm{Li}$ BEC-BCS crossover. The dashed line at 834 G marks the center of the broad ${}^6\mathrm{Li}$ Feshbach resonance and the dotted lines at 765 and 990 G indicate the strongly interacting regime, where $|k_F^{\mathrm{Li}}a|\ge 1$. The error bars represent the statistical errors from fitting the loss curves. Additional uncertainties arise from our limited knowledge of the size of the Li sample. On the BCS side this is negligible in comparison with the shown statistical errors, but on the BEC side it may introduce additional errors of up to a few 10%.

Figure 4

Thermalization of ${}^{40}\mathrm{K}$ in a ${}^6\mathrm{Li}$ bath. The temperature evolution of the ${}^{40}\mathrm{K}$ probe is shown at 1190 G (filled circles) and at 834 G (open circles). For comparison we also show the temperature of the ${}^6\mathrm{Li}$ bath measured at 1190 G. The error bars represent the fit errors from analyzing time-of-flight images.