An elementary optical gate for expanding entanglement web

TL;DR

This paper presents a simple optical gate that efficiently expands polarization entangled W states by adding two photons, using beamsplitters and ancillary photons, improving upon previous methods in efficiency and simplicity.

Contribution

Introduction of a new elementary optical gate that expands W states with higher efficiency and simpler setup compared to prior approaches.

Findings

Successfully expands W states by adding two photons.

Achieves better efficiency than previous methods.

Simplifies the implementation of W-state generation.

Abstract

We introduce an elementary optical gate for expanding polarization entangled W states, in which every pair of photons are entangled alike. The gate is composed of a pair of 50:50 beamsplitters and ancillary photons in the two-photon Fock state. By seeding one of the photons in an $n$-photon W state into this gate, we obtain an $(n+2)$-photon W state after post-selection. This gate gives a better efficiency and a simpler implementation than previous proposals for $\rm W$-state preparation.