  We propose a method for preparing maximal path entanglement with a definite
photon number N, larger than two, using projective measurements. In contrast
with the previously known schemes, our method uses only linear optics.
Specifically, we exhibit a way of generating four-photon, path-entangled states
of the form |4,0> + |0,4>, using only four beam splitters and two detectors.
These states are of major interest as a resource for quantum interferometric
sensors as well as for optical quantum lithography and quantum holography.
