  Selective truncation of Fock-state expansion of an optical field can be
achieved using projection synthesis. The process removes predetermined Fock
states from the input field by conditional measurement and teleportation. We
present a scheme based on multiport interferometry to perform projection
synthesis. This scheme can be used both as a generalized quantum scissors
device, which filters out Fock states with photon numbers higher than a
predetermined value, and also as a quantum punching device, which selectively
removes specific Fock states making holes in the Fock-state expansion of the
input field.
