Matter-wave collimation to picokelvin energies with scattering length and potential shape control

We study the impact of atomic interactions on an in-situ collimation method for matter-waves. Building upon an earlier study with ^87Rb, we apply a lensing protocol to ^39K where the atomic scattering length can be tailored by means of magnetic Feshbach resonances. Minimizing interactions, we show an enhancement of the collimation compared to the strong interaction regime observing a one-dimensional expansion corresponding to (340 ± 12) pK in our experiment. Our results are supported by an accurate simulation, describing the ensemble dynamics, which allows us to extrapolate a 2D ballistic expansion energy of (438 ± 77) pK from our measurements. We further use the simulation to study the behavior of various trap configurations for different interaction strengths. Based on our findings we propose an advanced scenario which allows for 3D expansion energies below 16 pK by implementing an additional pulsed delta-kick collimation directly after release from the trapping potential. Our results pave the way to realize ensembles with hundreds of thousands of particles and 3D expansion energies in the two-digit pK range in typical dipole trap setups required to perform ultra-precise measurements without the need of complex micro-gravity or long-baseline environments.