A7N: Precision control of a single impurity in a fermionic bath

Simon Stellmer

New since July 2020

The bi-polaron quasi-particle is an interesting concept in solid-state physics: two polarons interacting via a bath. While this scenario is discussed in the context of superconductivity, analogous simulations in cold-atom experiments still await realization. Working towards this long-term goal, we implement a novel impurity/bath system that allows for the observation of Friedel oscillations. These periodic density modulations are a witness of the impurity-bath interaction and can be used to probe the properties of the bath. As compared to solid-state systems, ultracold atoms constitute a very clean and controllable platform and allow for a study of the dynamic properties of Friedel oscillations.

Fig. 1: Visualization of Friedel oscillations in a fermionic bath around an impurity atom

We employ a bosonic impurity of the alkaline-earth-like element mercury immersed in a degenerate Fermi gas of the same element. Mercury appears to be an excellent candidate for these experiments, as it offers all the required properties: a large range of bosonic
and fermionic isotopes, highly isotope-selective transitions for addressing and trapping, a clock transition to probe minuscule energy shifts, and broad UV transitions for outstanding imaging resolution.

Fig. 2: Our first MOT of mercury, obtained on May 15, 2020