Le vendredi 4 décembre à 10H en vidéoconférence : https://youtu.be/Knf_ErXMCOk

Ultracold Fermi gases: Next generation experiment and impurity physics

This work includes two distinctive parts. The first concerns my participation in the construction of a new generation cold atoms machine in the team of ultracold fermion at Laboratoire Kastler Brossel. This experiment has the goal of studying strongly interacting fermionic gases of 6Li. A brief description of the experiment and the several cooling steps will be presented.
The second part includes two theoretical projects regarding the physics of an impurity immersed in a two-component Fermi gas. When an impurity is submerged in an interacting medium, its energy presents logarithmic divergence in its perturbative expansion. We use the Green functions formalism to understand the fundamental processes at the origin of this behavior.
In the second project, we study the phase diagram of an impurity immersed in a non-interacting double Fermi sea. This regime presents several fundamental states depending on the nature of interactions between the impurity and the fermionic components of the bath. We have shown, using a variational calculation, that there exists a phase transition of first order between the weakly interacting impurity-fermion interaction where a quasiparticle, called the polaron, is present, and the limit of stronger interactions where a bound state of three-particles, called a trimer, is present close to the Fermi surface. This project and its main result will be presented during the talk.