We propose an optical scheme to prepare large-scale entangled networks of W states. The scheme works by simultaneously fusing three polarization-encoded W states of arbitrary size via accessing only one qubit of each W state. It is composed of a Fredkin gate (controlled-swap gate), two fusion gates [as proposed in New J. Phys. 13, 103003 (2011)] and an H-polarized ancilla photon. Starting with three n-qubit W states, the scheme prepares a new W state with 3(n−1)-qubits after postselection if both fusion gates operate successfully, i.e. a four-fold coincidence at the detectors. The proposed scheme reduces the cost of creating arbitrarily large W states considerably when compared to previously reported schemes.
@article{arxiv.1402.3152,
title = {Fusing multiple W states simultaneously with a Fredkin gate},
author = {Fatih Ozaydin and Sinan Bugu and Can Yesilyurt and Azmi Ali Altintas and Mark Tame and Sahin Kaya Ozdemir},
journal= {arXiv preprint arXiv:1402.3152},
year = {2014}
}