Experimental multipartite entanglement and randomness certification of the W state in the quantum steering scenario

TL;DR

This paper experimentally demonstrates multipartite entanglement and certifies randomness in a three-qubit photonic W state using semi-device independent methods, relevant for quantum cryptography in asymmetric networks.

Contribution

It implements semi-device independent techniques to witness all entanglement types and analyzes randomness certification in a three-qubit W state.

Findings

Successfully certifies all entanglement types in a W state

Quantifies genuine randomness from bipartitions

Validates semi-device independent methods in photonic systems

Abstract

Recently [Cavalcanti \textit{et al.} Nat Commun \textbf{6}, 7941 (2015)] proposed a method to certify the presence of entanglement in asymmetric networks, where some users do not have control over the measurements they are performing. Such asymmetry naturally emerges in realistic situtations, such as in cryptographic protocols over quantum networks. Here we implement such "semi-device independent" techniques to experimentally witness all types of entanglement on a three-qubit photonic W state. Furthermore we analise the amount of genuine randomness that can be certified in this scenario from any bipartition of the three-qubit W state.