First observation of Feshbach resonances at very low magnetic field in a 133Cs fountain

For a long time, one of the main limitations of cesium atomic fountains has been the cold collision frequency shift. By using a method based on a transfer of population by adiabatic passage (AP) allowing to prepare cold atomic samples with a well defined ratio of atomic density as well as atom number we have a better measurement of this effect. By improving the method we found out some unexpected properties of cold collisions, confirming that ¹³³Cs is a rich atom to study cold collisions. Those results lead to fine comparisons with cold collision theory and may constraint some parameters of cesium.