Title: A simple scheme for expanding a polarization-entangled<i>W</i>state by adding one photon
Abstract: We propose a simple scheme for expanding a polarization-entangled W state. By mixing a single photon and one of the photons in an n-photon W state at a polarization-dependent beam splitter (PDBS), we can obtain an (n + 1)-photon W state after post-selection. Our scheme also opens the door to generating n-photon W states using single photons and linear optics.