An experimental scheme for preparing a polarization entangled W states from four photons emitted by parametric down-conversion is proposed. We consider two different configurations and a method of improving the yield by using single photon sources. In the proposed scheme, one uses only linear optical elements and photon detectors, so that this scheme is feasible by current technologies.
@article{arxiv.quant-ph/0208162,
title = {Polarization Entangled W State using Parametric Down-Conversion},
author = {Takashi Yamamoto and Kiyoshi Tamaki and Masato Koashi and Nobuyuki Imoto},
journal= {arXiv preprint arXiv:quant-ph/0208162},
year = {2009}
}