  We study the operation of linear optics schemes for entanglement distribution
based on nonlocal photon subtraction when input states, produced by imperfect
single-photon sources, exhibit both vacuum and multiphoton contributions. Two
models for realistic photon statistics with radically different properties of
the multiphoton "tail" are considered. The first model assumes occasional
emission of double photons and linear attenuation, while the second one is
motivated by heralded sources utilizing spontaneous parametric down-conversion.
We find conditions for the photon statistics that guarantee generation of
entanglement in the relevant qubit subspaces and compare it with classicality
criteria. We also quantify the amount of entanglement that can be produced with
imperfect single-photon sources, optimized over setup parameters, using as a
measure entanglement of formation. Finally, we discuss verification of the
generated entanglement by testing Bell's inequalities. The analysis is carried
out for two schemes. The first one is the well-established one-photon scheme,
which produces a photon in a delocalized superposition state between two nodes,
each of them fed with one single photon at the input. As the second scheme, we
introduce and analyze a linear-optics analog of the robust scheme based on
interfering two Stokes photons emitted by atomic ensembles, which does not
require phase stability between the nodes.
