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We report on the study of binary collisions between quantum droplets formed by an attractive mixture of ultracold atoms. We distinguish two main outcomes of the collision, i.e., merging and separation, depending on the velocity of the colliding pair. The critical velocity vc that discriminates between the two cases displays a different dependence on the atom number N for small and large droplets. By comparing our experimental results with numerical simulations, we show that the nonmonotonic behavior of vc is due to the crossover from a compressible to an incompressible regime, where the collisional dynamics is governed by different energy scales, i.e., the droplet binding energy and the surface tension. These results also provide the first evidence of the liquidlike nature of quantum droplets in the large N limit, where their behavior closely resembles that of classical liquid droplets. G. Ferioli et al., |
Pushing the limits of atom interferometry...The system we want to realize is a Mach-Zender spatial interferometer operating with trapped Bose-Einstein condensates (BECs). Phase diffusion caused by interatomic collisions are suppressed implementing BECs with tunable interactions in ultra-stable optical potentials. Entangled states can be used to improve the sensitivity of the sensor beyond the standard quantum limit to ideally reach the ultimate, Heisenberg, limit set by quantum mechanics. Our project aims at developing a sensor with unprecedented spatial resolution able to compete with, and eventually overcome, state-of-the-art interferometers with cold (non condensed) atomic waves.