Experimental few-copy multi-particle entanglement detection

TL;DR

This paper introduces a resource-efficient probabilistic framework for detecting multi-particle entanglement in large quantum states, verified experimentally on a six-qubit photonic cluster state with high confidence using few copies.

Contribution

It develops a generic method to convert any entanglement witness into a probabilistic scheme, enabling efficient verification of large-scale quantum entanglement.

Findings

Entanglement can be certified with 99.74% confidence using only 20 copies.

Genuine six-qubit entanglement verified with at least 99% confidence using 112 copies.

The protocol is practical for large quantum devices due to low copy requirements.

Abstract

Quantum technologies lead to a variety of applications that outperform their classical counterparts. In order to build a quantum device it must be verified that it operates below some error threshold. Recently, because of technological developments which allow for the experimental realization of quantum states with increasing complexity, these tasks must be applied to large multi-qubit states. However, due to the exponentially-increasing system size, tasks like quantum entanglement verification become hard to carry out in such cases. Here we develop a generic framework to translate any entanglement witness into a resource-efficient probabilistic scheme. We show that the confidence to detect entanglement grows exponentially with the number of individual detection events. To benchmark our findings, we experimentally verify the presence of entanglement in a photonic six-qubit cluster state generated using three single-photon sources operating at telecommunication wavelengths. We find that its presence can be certified with at least 99.74% confidence by detecting 20 copies of the quantum state. Additionally, we show that genuine six-qubit entanglement is verified with at least 99% confidence by using 112 copies of the state. Our protocol can be carried out with a remarkably low number of copies, making it a practical and applicable method to verify large-scale quantum devices.