  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 multi-photon polarization entangled states.
