Laser-cooled atomic samples provide highly controllable and versatile platforms to study complex phenomena. The ion trapping group in Marseilles studies laser-cooled calcium ions Ca+ trapped in linear radio-frequency (rf) traps. At temperatures lower than 1 K the trapped ions form a regular structure, called a Coulomb crystal, minimizing the total energy, as shown on the figure, which displays the fluorescence of the ions imaged by a camera. By playing with the lasers addressing the ions it is possible to shelve part of the cloud in a “dark state”, triggering a phase separation between bright and dark ions. By studying this process one can measure experimentally the self-diffusion coefficients in a one-component strongly correlated plasma, which is the topic of this internship offer.