In this paper, we develop a simple model describing inherent photon-number
noise in Rarity-Tapster type interferometers. This noise is caused by
generating photon pairs in the process of spontaneous parametric
down-conversion and adding a third photon by attenuating fundamental laser mode
to single-photon level. We experimentally verify our model and present
resulting signal to noise ratios as well as obtained three-photon generation
rates as functions of various setup parameters. Subsequently we evaluate impact
of this particular source of noise on quantum teleportation which is a key
quantum information protocol using this interferometric configuration.Comment: 7 pages, 5 figure