  By sending many two-level atoms through a cavity resonant with the atomic
transition, and letting the interaction times between the atoms and the cavity
be randomly distributed, we end up with a predetermined Fock state of the
electromagnetic field inside the cavity if we perform after the interaction
with the cavity a conditional measurement of the internal state of each atom in
a coherent superposition of its ground and excited states. Differently from
previous schemes, this procedure turns out to be very stable under fluctuations
in the interaction times.
