Creation of maximally entangled photon-number states using optical fiber multiports

We theoretically demonstrate a method for producing the maximally path-entangled state $(1/\sqrt{2})(|N,0\mathrm{}〉+\exp [\mathrm{iN}\phi ]|0,N〉)$ using intensity-symmetric multiport beam splitters, single photon inputs, and either photon-counting postselection or conditional measurement. The use of postselection enables successful implementation with non-unit efficiency detectors. We also demonstrate how to make the same state more conveniently by replacing one of the single photon inputs by a coherent state.