Closing loopholes of measurement-device-independent nonlinear entanglement witnesses

TL;DR

This paper analyzes the robustness of measurement-device-independent nonlinear entanglement witnesses (MDI-NEWs) against experimental loopholes, proposing bounds and identifying noise conditions under which they reliably detect entanglement.

Contribution

It introduces bounds for entanglement detection considering detection loopholes and noise, enhancing the reliability of MDI-NEWs in practical quantum experiments.

Findings

Bounds for entanglement detection under detection loopholes.

Identification of noise conditions compatible with entanglement guarantees.

Comparison showing MDI-NEWs are less robust than linear witnesses under certain noise.

Abstract

The concept of entanglement witnesses form a useful technique to detect entanglement in realistic quantum devices. Measurement-device-independent nonlinear entanglement witnesses (MDI-NEWs) are a kind of entanglement witnesses which eliminate dependence on the correct alignments of measurement devices for guaranteeing the existence of entanglement and also detect more entangled states than their linear counterparts. While this method guarantees entanglement independent of measurement alignments, they are still prone to serving wrong results due to other loopholes. Here we study the response of MDI-NEWs to two categories of faults occurring in experiments. In the first category, the detection loophole, characterized by lost and additional events of outcomes of measurements, is investigated, and bounds which guarantee entanglement are obtained in terms of the efficiency of measurement being performed. In the second category, we study noise associated with the sets of additional quantum inputs required in MDI-NEW scenarios. In this case, a type of noise is identified which still allows the MDI-NEWs to guarantee entanglement. We also show that MDI-NEWs are less or equally robust in comparison to their linear counterparts under the same noise in additional quantum inputs, although the former group detects a larger volume of entangled states in the noiseless scenario than their linear cousins.