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

Abstract

We study the impact of atomic interactions on an in-situ collimation method for matter-waves. Building upon an earlier study with $^{87}$Rb, we apply a lensing protocol to $^{39}$K 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, realizing ballistic 2D expansion energies of 438(77) pK in our experiment. Our results are supported by an accurate simulation, describing the ensemble dynamics, which we further use 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 achieve state-of-the-art quantum state in typical dipole trap setups required to perform ultra-precise measurements without the need of complex micro-gravity or long baselines environments