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.

A close look to the coupled dipole dynamics of a bosonic mixture

K/Rb Lab

We studied the coupled dipole dynamics of a 41K-87Rb bosonic mixture as a function of the interspecies interaction. We measured both the frequency and the composition of the two dipole eigenmodes, from the weakly to the strongly attractive regime. For sufficiently strong interactions, even beyond the mean-field collapse, we found that the two condensates oscillate with the same frequency that depends only on the bare trap frequencies and the total mass of each species. This feature has been tested for a broad range of species population imbalance and has been demonstrated to agree with theoretical predictions.

L. Cavicchioli et al.
Dipole dynamics of an interacting bosonic mixture
Phys. Rev. Research 4, 043068 (2022)

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