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Polarons are quasi-particles that emerge when impurity particle is mixed with the low-energy excitations of a medium. Here the authors study the case of atom-ion quantum mixtures and identify three separate bipolaronic regimes which can arise depending on the interaction range and strength.

An impurity introduced to a many-body quantum environment gets dressed by excitations and it is of a particular interest to understand the limits of the quasi-particle description. The authors theoretically and numerically study an ionic impurity immersed in a weakly interacting gas of bosonic atoms and demonstrate the existence of two main phases of a polaronic regime for weak interactions, and a strongly correlated state with many bosons bound to the ion.

Investigating the collisional behaviour of molecules on the quantum level is the key in understanding and controlling chemical reactions. Here the authors measure inelastic collision rates for ultracold Rb2dimers in precisely defined quantum states and show that the rates can be tuned via external parameters.