Observation of fermion-mediated interactions between bosonic atoms.

Abstract

In high-energy and condensed-matter physics, particle exchange has an essential role in the understanding of long-range interactions and correlations. For example, the exchange of massive bosons leads to the Yukawa potential^1,2, and phonon exchange between electrons gives rise to Cooper pairing in superconductors³. Here we show that, when a Bose-Einstein condensate of caesium atoms is embedded in a degenerate Fermi gas of lithium atoms, interspecies interactions can give rise to an effective trapping potential, damping, and attractive boson-boson interactions mediated by fermions. The latter, which is related to the Ruderman-Kittel-Kasuya-Yosida mechanism⁴, results from a coherent three-body scattering process. Such mediated interactions are expected to form new magnetic phases⁵ and supersolids⁶. We show that under suitable conditions, the mediated interactions can convert a stable Bose-Einstein condensate into a train of 'Bose-Fermi solitons'^7,8. The predicted long-range nature of the mediated interactions opens up the possibility of correlating distant atoms and preparing new quantum phases.