We present the first experimental demonstration of simultaneous trapping of electrons and ions in the same spatial region. Confinement of particles with opposite charges and very different mass in the combined trap represents an important step towards the synthesis of antihydrogen.

We have trapped ${}^{40}\mathrm{K}$ in a vapor-cell magneto-optical trap starting from a natural abundance sample. This rare, weakly radioactive atom is a fermion. The number of trapped atoms is approximately 8000, with a density of $\sim {10}^8$ atoms/${\mathrm{cm}}^3$. Contrary to what is observed for the other isotopes of potassium, our data indicate that temperatures lower than the Doppler-cooling limit can be reached for ${}^{40}\mathrm{K}$. We discuss the interest of these results in view of possible experiments to study a degenerate Fermi gas.