Ultracold Heteronuclear Fermi-Fermi Molecules

We report on the first creation of ultracold bosonic heteronuclear molecules of two fermionic species, ${}^6\mathrm{Li}$ and ${}^{40}\mathrm{K}$, by a magnetic field sweep across an interspecies $s$-wave Feshbach resonance. This allows us to associate up to $4\times {10}^4$ molecules with high efficiencies of up to 50%. Using direct imaging of the molecules, we measure increased lifetimes of the molecules close to resonance of more than 100 ms in the molecule-atom mixture stored in a harmonic trap.

Figure 1

Lifetime of the ${}^6\mathrm{Li}$-${}^{40}\mathrm{K}$ mixture as a function of the magnetic field in the vicinity of a FR between $\mathrm{Li}|1/2,1/2⟩$ and $\mathrm{K}|9/2,-5/2⟩$.

Figure 2

Adiabaticity of the molecule conversion process as a function of the inverse sweep rate of the magnetic field strength. The decrease in atom number is attributed to molecule association. The lines represent an exponential fit based on the Landau-Zener theory.

Figure 3

Reconversion process of molecules to unbound atoms as a function of the final magnetic field strength. First, molecules are associated by an adiabatic sweep from $B_1$ to $B_2$. Then, the molecules are adiabatically reconverted to unbound atoms by a sweep to a variable final value $B_3$. The lines represent an empirical fit using an error function.

Figure 4

(a) Direct simultaneous absorption imaging of the molecular and atomic cloud after separation by a Stern-Gerlach force during time of flight (TOF). (b) Energies of molecular states (solid lines) and free atoms (dashed line): The molecular state has almost vanishing magnetic moment at the Feshbach resonance (encircled region).

Figure 5

Characterization of the molecular $1/e$ lifetime ${\tau }_{\mathrm{mol}}$ in the molecule-atom mixture as a function of the magnetic field strength. In addition, ${\tau }_{\mathrm{mol}}{n}_{\mathrm{mol}}$ is plotted, where $n_{\mathrm{mol}}$ is the initial molecular density, averaged over the cloud.