  Quantum information processing using photons has recently been stimulated by
the suggestion to use linear optics, single photon sources and detectors. The
recent work by Knill has also shown that errors in photon detectors leads to a
high error rate threshold (around 29%). An important missing element are good
single photon sources. In this paper we show how to make a single photon source
using squeezed states, linear optics and conditional measurement. We use
degenerate squeezed vacuum states, in contrast to the normal non-degenerate
squeezed vacuum states used for single photon production. We show that we can
get a photon with certainty when detectors click appropriately, the last event
happening up to around 25% of the time. We also show the robustness of this
method with respect to a variety of potential imperfections.
