Measuring concurrence in qubit Werner states without aligned reference frame

TL;DR

This paper investigates how to measure genuine multipartite entanglement in qubit Werner states without requiring a shared reference frame or calibrated devices, combining theoretical analysis and experimental validation.

Contribution

It introduces a method to quantify genuine concurrence without aligned reference frames, linking it to nonlocal volume, and demonstrates this experimentally.

Findings

Genuine concurrence can be measured without a shared reference frame.

A relation between genuine concurrence and nonlocal volume is established.

Experimental results confirm the theoretical predictions.

Abstract

The genuine concurrence is a standard quantifier of multipartite entanglement, detection and quantification of which still remains a difficult problem from both theoretical and experimental point of view. Although many efforts have been devoted toward the detection of multipartite entanglement (e.g., using entanglement witnesses), measuring the degree of multipartite entanglement, in general, requires some knowledge about an exact shape of a density matrix of the quantum state. An experimental reconstruction of such density matrix can be done by full state tomography which amounts to having the distant parties share a common reference frame and well calibrated devices. Although this assumption is typically made implicitly in theoretical works, establishing a common reference frame, as well as aligning and calibrating measurement devices in experimental situations are never trivial tasks. It is therefore an interesting and important question whether the requirements of having a shared reference frame and calibrated devices can be relaxed. In this work we study both theoretically and experimentally the genuine concurrence for the generalized Greenberger-Horne-Zeilinger states under randomly chosen measurements on a single qubits without a shared frame of reference and calibrated devices. We present the relation between genuine concurrence and so-called nonlocal volume, a recently introduced indicator of nonlocality.