The two modes of the Einstein-Podolsky-Rosen quadrature entangled state generated by parametric down-conversion interfere on a beam splitter of variable splitting ratio. Detection of a photon in one of the beam splitter output channels heralds preparation of a signal state in the other, which is characterized using homodyne tomography. By controlling the beam splitting ratio, the signal state can be chosen anywhere between the single-photon and squeezed state.
@article{arxiv.0912.1552,
title = {A bridge between the single-photon and squeezed-vacuum state},
author = {Nitin Jain and S. R. Huisman and Erwan Bimbard and A. I. Lvovsky},
journal= {arXiv preprint arXiv:0912.1552},
year = {2014}
}