Résumé
Coulomb interactions of few electrons confined in a disk-shaped quantum dot, with a large magnetic field perpendicular to the dot, produce a fully spin polarized ground state. In the presence of an electric field also perpendicular to the dot and coupling spin and orbit (Rashba term), we find that the first excited state is a spin exciton with a reversed spin at the center of the dot. We explore the analogy with the quantum Hall ferromagnet at filling close to one, which is spin polarized and has skyrmions as collective low lying excitations. The energy of the spin exciton can be tuned with the electric field, and infrared radiation can provide energy and angular momentum to excite it. In the quantum dot the gap is finite and is tuned by the Rashba coupling. This opens up many unexpected possibilities of controlling the electron spin density at the dot and influencing the underlying nuclear spins via hyperfine interaction.