Selective truncations of an optical state using projection synthesis
  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. 
Adam Miranowicz, Sahin Kaya Ozdemir, Jiri Bajer, Masato Koashi,   Nobuyuki Imoto