Demonstration of local expansion toward large-scale entangled webs

TL;DR

This paper presents an optical gate that can expand polarization-based W states by acting on a single qubit, successfully generating larger entangled states with high fidelity and confirming pairwise entanglement.

Contribution

The authors introduce a universal optical gate capable of expanding W states of any size by accessing only one qubit, a significant advancement in entanglement manipulation.

Findings

Generated three-photon and four-photon W states with high fidelity.

Confirmed pairwise entanglement in all qubit pairs, including untouched ones.

Demonstrated the gate's applicability to any size of W states.

Abstract

We demonstrate an optical gate that increases the size of polarization-based W states by accessing only one of the qubits. Using this gate, we have generated three-photon and four-photon W states with fidelities $0.836\pm 0.042 $ and $0.784\pm 0.028$, respectively. We also confirmed existence of pairwise entanglement in every pair of the qubits including the one that was left untouched by the gate. The gate is applicable to any size of W states and hence is a universal tool for expanding entanglement.