Measurement-device-independent nonlinear entanglement witnesses

TL;DR

This paper introduces measurement-device-independent nonlinear entanglement witnesses that can detect a broader class of entangled states without relying on perfect measurement devices, improving robustness over traditional methods.

Contribution

It presents the first measurement-device-independent nonlinear entanglement witnesses capable of detecting non-positive partial transpose and bound entangled states.

Findings

Certify entanglement of the same states as their device-dependent counterparts.

Outperform linear entanglement witnesses in detection capabilities.

Enhance robustness against measurement imperfections.

Abstract

Entanglement witnesses are one of the most effective methods to detect entanglement. It is known that nonlinear entanglement witnesses provide better entanglement detection than their linear counterparts, in that the former detect a strictly larger subset of entangled states than the latter. Whether linear or nonlinear, the method is measurement-device dependent, so that imperfect measurements may cause false certification of entanglement in a shared state. Measurement-device-independent entanglement witnesses provide an escape from such measurement dependence of the entanglement detection for linear entanglement witnesses. Here we present measurement-device-independent nonlinear entanglement witnesses for non-positive partial transpose entangled states as well as for bound entangled states with positive partial transpose. The constructed measurement-device-independent nonlinear entanglement witnesses certify the entanglement of the same sets of entangled states as their device-dependent parents do, and therefore are better than the linear entanglement witnesses, device-independent or otherwise.