Witnessing Multipartite Entanglement without Entanglement Witness Operators

TL;DR

This paper introduces a new method to detect multipartite entanglement in quantum systems by measuring their response to collective evolution, avoiding the need for entanglement witness operators or full state tomography.

Contribution

It presents a novel, efficient protocol for witnessing multipartite entanglement using only two measurement settings, applicable to various experimental platforms.

Findings

Successfully demonstrated in ion and photon experiments

Does not require measurement efficiencies or state reconstruction

Applicable to any number of parties

Abstract

Quantum mechanics predicts the existence of correlations between composite systems -- multipartite entanglement (ME) -- that, while puzzling our physical intuition, enable technologies not accessible in a classical world. Notwithstanding, there is still no efficient general method to theoretically quantify and experimentally detect ME. Here we propose a novel paradigm based on the measurement of the statistical response of a quantum systems to a collective parametric evolution. As a major difference with respect to current approaches based on the implementation of entanglement witness operators, we witness ME without relying on measurement efficiencies or tomographic reconstructions of the quantum state. The protocol requires only two settings for any number of parties. To illustrate its user-friendliness we demonstrate ME in different experiments with ions and photons by analyzing published data on fidelity visibilities and averaged observables.