Verifying genuine multipartite entanglement of the whole from its separable parts

TL;DR

This paper experimentally demonstrates that genuine multipartite entanglement in a three-qubit state can be verified solely from its two-qubit reduced states, confirming the possibility of detecting global quantum properties from local parts.

Contribution

It provides the first experimental verification that global multipartite entanglement can be certified using only separable two-qubit reductions, advancing quantum entanglement detection methods.

Findings

Genuine multipartite entanglement can be certified from two-qubit reductions.

Experimental implementation using linear optical circuits.

Validation of theoretical predictions on entanglement detection.

Abstract

We prove experimentally the predicted existence of a three-qubit quantum state with genuine multipartite entanglement which can be certified solely from its separable two-qubit reduced density matrices. The qubits are encoded into different degrees of freedom of a pair of correlated photons and the state is prepared by letting the photons to propagate through a linear optical circuit. The presence of genuine multipartite entanglement is verified by finding numerically a fully decomposable entanglement witness acting nontrivially only on the reductions of the global state. Our result confirms viability of detection of emerging global properties of composite quantum systems from their parts which lack the properties.