Quantum scattering in a juggling atomic fountain

We demonstrate a juggling atomic fountain by launching two laser-cooled balls of ¹³³Cs atoms in rapid succession. The atoms collide near the top of the fountain and, by varying the delay between launches, we scan the collision energy from 19 to 150μK. We measure the differential scattering cross section and isolate the contributions from different partial waves including their interferences. We observe the s-wave energy dependence and the p-wave scattering threshold. We infer a triplet s-wave scattering length of –400a₀ and a p wave of (–107a₀)³ for |F = 4, m = 4⟩ + |3,3⟩.