Linear optical implementation of a single-mode quantum filter and generation of multiphoton polarization entangled states

We propose a scheme to implement a single-mode quantum filter, which selectively eliminates the one-photon state in a quantum state alpha\0] + beta\1) + gamma\2]. The vacuum state and the two-photon state are transmitted without any change. This scheme requires single-photon sources, linear optical elements, and photon detectors. Furthermore, we demonstrate how this filter can be used to realize a two-qubit projective measurement and to generate multiphoton polarization entangled states.