Rapid generation of all-optical ³⁹K Bose-Einstein condensates using a low-field Feshbach resonance

Ultracold potassium is a promising candidate for quantum technological applications as it allows changing intra-atomic interactions via low-field magnetic Feshbach resonances. However, the realization of high-flux sources of Bose-Einstein condensates remains challenging due to the necessity of optical trapping to use magnetic fields as external degree of freedom. We investigate the production of all-optical ³⁹K Bose-Einstein condensates under different scattering lengths using a low-field Feshbach resonance near 33 G. By tuning the scattering length in a range between 75 a₀ and 300 a₀ we demonstrate a trade off between evaporation speed and final atom number and decrease our evaporation time by a factor of 5 while approximately doubling the atomic flux. To this end, we are able to produce fully condensed ensembles with 5×10⁴ atoms within 850 ms evaporation time at a scattering length of 232 a₀ and 1.6×10⁵ atoms within 4 s at 158 a₀, respectively. We deploy a numerical model to analyse the flux and atom number scaling with respect to scattering length, identify current limitations and simulate the optimal performance of our setup. Based on our findings we describe routes towards high-flux sources of ultra-cold potassium for inertial sensing.