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 a Feshbach resonance. We investigate the production of all-optical 39 K 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 × 10 4 atoms within 850 ms evaporation time at a scattering length of 232 a0 and 1.6 × 10 5 atoms within 4 s at 158 a0, respectively. We analyze the flux scaling with respect to collision rates and describe routes towards high-flux sources of ultra-cold potassium for inertial sensing.

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Ultracold potassium is an interesting candidate for quantum technology applications and fundamental research as it allows controlling 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 free parameters. We investigate the production of all-optical 39 K Bose-Einstein condensates with different scattering lengths using a Feshbach resonance near 33 G. By tuning the scattering length in a range between 75a 0 and 300a 0 we demonstrate a tradeoff between evaporation speed and final atom number and decrease our evaporation time by a factor of 5 while approximately doubling the evaporation flux. To this end, we are able to produce fully condensed ensembles with 5.8 × 10 4 atoms within 850-ms evaporation time at a scattering length of 232a 0 and 1.6 × 10 5 atoms within 3.9 s at 158a 0 , respectively. We deploy a numerical model to analyze 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 ultracold potassium for inertial sensing.