On witnessing arbitrary bipartite entanglement in a measurement device independent way

TL;DR

This paper develops a universal measurement device independent scheme for detecting bipartite entanglement in two-qubit states, focusing on NPT entanglement and analyzing robustness under noise, advancing quantum entanglement detection methods.

Contribution

It introduces a universal detection scheme for two-qubit entanglement that is measurement device independent, extending previous methods and analyzing robustness against noise.

Findings

Provides universal witness operators for NPT entanglement detection.

Conjectures no universal witness exists for PPT entangled states.

Analyzes robustness of detection schemes under input and measurement noise.

Abstract

Experimental detection of entanglement of an arbitrary state of a given bipartite system is crucial for exploring many areas of quantum information. But such a detection should be made in a device independent way if the preparation process of the state is considered to be faithful, in order to avoid detection of a separable state as entangled one. The recently developed scheme of detecting bipartite entanglement in a measurement device independent way [Phys. Rev. Lett {\bf 110}, 060405 (2013)] does require information about the state. Here by using Auguisiak et al.'s universal entanglement witness scheme for two-qubit states [Phys. Rev. A {\bf 77}, 030301 (2008)], we provide a universal detection scheme for two-qubit states in a measurement device independent way. We provide a set of universal witness operators for detecting NPT-ness(negative under partial transpose) of states in a measurement device independent way. We conjecture that no such universal entanglement witness exists for PPT(positive under partial transpose) entangled states. We also analyse the robustness of some of the experimental schemes of detecting entanglement in a measurement device independent way under the influence of noise in the inputs (from the referee) as well as in the measurement operator as envisazed in ref. [Phys. Rev. Lett {\bf 110}, 060405 (2013)].