Multipartite entanglement detection with minimal effort

TL;DR

This paper introduces a method to detect multipartite entanglement efficiently, requiring only a constant number of measurements regardless of the number of qubits, demonstrated on four-qubit states.

Contribution

The authors present a new scheme for constructing entanglement witnesses that need only a fixed number of measurements, independent of system size, for certain important quantum states.

Findings

Successfully detected four-partite entanglement with only two measurement settings.

Applicable to states like GHZ, cluster, and Dicke states.

Experimental validation on four-qubit states confirms effectiveness.

Abstract

Certifying entanglement of a multipartite state is generally considered as a demanding task. Since an $N$ qubit state is parametrized by $4^{N}-1$ real numbers, one might naively expect that the measurement effort of generic entanglement detection also scales exponentially with $N$. Here, we introduce a general scheme to construct efficient witnesses requiring a constant number of measurements independent of the number of qubits for states like, e.g., Greenberger-Horne-Zeilinger states, cluster states and Dicke states. For four qubits, we apply this novel method to experimental realizations of the aforementioned states and prove genuine four-partite entanglement with two measurement settings only.