  We show that it is possible to add or subtract many photons from a cavity
field by interacting it resonantly with a two-level atom. The atom, after
entangling with the field inside the cavity and exiting it, may be measured in
one of the Schmidt states, producing a multiphoton process (in the sense that
can add or annihilate more photons than a single transition allows), i.e.,
adding or subtracting several photons from the cavity field.
