Reliable experimental quantification of bipartite entanglement without reference frames

TL;DR

This paper introduces a method for reliably quantifying bipartite entanglement without shared reference frames, using simple local measurements that outperform traditional state tomography in experimental settings.

Contribution

The authors propose reference frame independent expressions for entanglement quantification that are experimentally testable and more reliable than state tomography, applicable to various entanglement measures.

Findings

Bound on concurrence obtained directly from measurements

Experimental demonstration of improved reliability over state tomography

Application to entropy measures like Renyi and von Neumann entropies

Abstract

Simply and reliably detecting and quantifying entanglement outside laboratory conditions will be essential for future quantum information technologies. Here we address this issue by proposing a method for generating expressions which can perform this task between two parties who do not share a common reference frame. These reference frame independent expressions only require simple local measurements, which allows us to experimentally test them using an off-the-shelf entangled photon source. We show that the values of these expressions provide bounds on the concurrence of the state, and demonstrate experimentally that these bounds are more reliable than values obtained from state tomography since characterizing experimental errors is easier in our setting. Furthermore, we apply this idea to other quantities, such as the Renyi and von Neumann entropies, which are also more reliably calculated directly from the raw data than from a tomographically reconstructed state. This highlights the relevance of our approach for practical quantum information applications that require entanglement.