Sometimes, the most familiar objects display unexpected features. We found ourselves in this surprising situation looking at a polarized cloud of Lithium 6 in a quadrupole trap. With a fermionic statistics, Li6 behaves at low temperatures as an ideal gas and one could think that the properties on such a non-interacting system are straightforward.

Thermalisation is usually associated to collisions between particles. However, in a quadrupole potential, the complex single particle trajectories can lead to chaotic dynamics, inducing a transfer of the center-of-mass motion to the internal energy of the cloud. Even if a stationary state can be achieved, to which extend can it correspond to a real thermal equilibrium of the system?

In this talk, I will discuss the dynamics of a spin polarized Li cloud in a quadrupole trap and the quasi thermalisation properties of this system.