  We present the experimental generation of tunable entanglement between
distinct field modes by the delocalized addition of a single photon. We show
that one can preserve a high degree of entanglement even between
macroscopically populated modes and illustrate this concept by adding a single
photon to two modes containing identical coherent states of growing amplitude.
Discorrelation, a new joint statistical property of multimode quantum states,
is also experimentally demonstrated here for the first time.
