Observation of Cold Collisions between Trapped Ions and Trapped Atoms

We study cold collisions between trapped ions and trapped atoms in the semiclassical (Langevin) regime. Using Yb(+) ions confined in a Paul trap and Yb atoms in a magneto-optical trap, we investigate charge-exchange collisions of several isotopes over three decades of collision energies down to 3 mu eV (k(B)x35 mK). The minimum measured rate coefficient of 6x10(-10) cm(3) s(-1) is in good agreement with that derived from a Langevin model for an atomic polarizability of 143 a.u.