We propose a simple probabilistic optical gate to expand polarization entangled W states. The gate uses one polarization-dependent beamsplitter and a horizontally polarized single photon as an ancilla. The gate post-selectively expands N-photon W states to (N+1)-photon W states. A feasibility analysis considering the realistic experimental conditions show that the scheme is within the reach of the current quantum optical technologies.
@article{arxiv.0810.2850,
title = {Local expansion of photonic W state using a polarization dependent beamsplitter},
author = {Toshiyuki Tashima and Sahin Kaya Ozdemir and Takashi Yamamoto and Masato Koashi and Nobuyuki Imoto},
journal= {arXiv preprint arXiv:0810.2850},
year = {2010}
}