Interactions Between Bosons Immersed in a Fermi Sea

When a Bose-Einstein condensate is embedded in a degenerate Fermi gas, the fermionic environment induces new types of correlations between the condensed atoms. For example, bosons can interact at long range through excitations of the Fermi surface in a manner analogous to the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism in solids. This gives rise to an effective interaction predicted to oscillate between attraction and repulsion at a length scale set by the Fermi momentum. These fermion-mediated interactions can lead to long range coupling between bosons as well as effective few-body interactions between bosons.

We study fermion-mediated interactions using quantum degenerate mixtures of bosonic ¹³³Cs and fermionic ⁶Li, where the much heavier bosonic atoms are fully immersed in the degenerate Fermi gas. Using a high resolution microscope and a digital micro-mirror device, we are able to image and manipulate the mixture at the one micron length scale. We will discuss progress towards the observation of effective three-body interactions between bosons and future experiments aimed at the direct observation of the long-ranged interaction potential.