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Just as a thin water jet emerging from a tap, a quantum atomic filament may break up into droplets: surprisingly, under some circumstances, quantum gases behave like liquids. In our lab, we prepare a quantum droplet of 41K and 87Rb, and release it in an optical waveguide. The droplet expands along the waveguide up to a critical length, and then splits into two or more sub-droplets. Our results can be explained in terms of capillary instability, previously observed in a variety of physical systems, including ordinary liquids and superfluid helium, but not yet in the ultracold gas realm. Getting curious? Look it up on the arxiv! L. Cavicchioli et al. |
Considering the hurdles of experiments with more than one atomic species, the temptation arises of rephrasing Arthur L. Schawlow: "Double-species Bose-Einstein condensates are condensates with one species too many". We think otherwise. Quantum mixtures allow the investigation of a wealth of genuinely quantum phenomena: mixed phases of superfluids and Mott insulators, impurities and polarons, chemistry at zero-temperature.