Interaction control in ultracold Fermi-Fermimixtures (Vol. 42, No. 3)

Many present-day experiments on ultracold quantum gases crucially rely on the ability to control the interparticle interaction via Feshbach resonances [C. Chin et al., Rev. Mod. Phys. 82, 1225 (2010)]. Such resonances occur when colliding atoms couple to a bound molecular state and manifest themselves in a pronounced dependence of the scattering length on the magnetic field (Fig.). This phenomenon provides experimentalists with a unique "tuning knob" to control the two-body, few-body, and many-body properties of the system.

Ultracold mixtures of two fermionic species hold great promise for synthesizing novel types of few- and many body quantum states, including exotic types of superfluids. The investigation of such systems has been pursued in the collaborative project FerMix in the network EuroQUAM (an ESF EUROCORE). The prime candidate for experimental realizations is a combination of the fermionic isotopes ⁶Li and ⁴⁰K. The article presents a state-of-the-art characterization of Feshbach resonances in a mixture of two Fermi gases of ⁶Li and ⁴⁰K. A thorough case study is reported for a particularly promising resonance near a magnetic field strength of 155G, and the comparison of experimental results with theory highlights the high understanding gained for the system. A survey of other resonances allows experimentalists to identify the most suited “tuning knobs” in such Fermi-Fermi systems.

The deep understanding of the collisional properties in the ultracold domain opens towards all applications concerning complex quantum states of strongly interacting fermionic matter.