  It is generally assumed that for ionization processes, which occur in slow
atomic collisions, the coupling of the colliding system to the quantum
radiation field is irrelevant. Here we show, however, that -- contrary to
expectations -- such a coupling can strongly influence ionization of a beam of
atomic species A slowly traversing a gas of atomic species B excited by a weak
laser field. Moreover, this coupling becomes even more important when the
collision velocity increases, getting comparable or exceeding the typical
electron orbiting velocities in A and B. Our results imply furthermore that the
Breit interaction can, in fact, dominate over the Coulomb interaction at very
low energies.
