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Crossover from a BEC to a macrodroplet

(c) of image: Harald Ritsch

Now in Physical Review X!

Together with our theory colleagues from Hannover (Luis Santos and Falk Wächtler), we have investigated the formation of a macrodroplet state in an ultracold bosonic gas of erbium atoms. Our paper has been now published in PRX and featured in Physics! MORE

By precisely changing the s-wave scattering length below the dipolar length, defined by the dipole-dipole interaction, we observe a smooth crossover of the ground state from a dilute Bose-Einstein condensate to a dense macrodroplet of more than 20.000atoms. By comparing collective excitations and loss features with numerical simulations, we could show, that quantum fluctuations play the stabilizing role that prevents the ultracold gas from becoming unstable, as naively expected in the standard meanfield picture. In another set of experiments, we perform expansion measurements and could show that although self-bound solutions are prevented by losses, the interplay between quantum stabilization and losses results in a minimal time-of-flight expansion velocity for a finite s-wave scattering length.

Link to paper