Entanglement witnessing with untrusted detectors

TL;DR

This paper introduces a new method for entanglement detection that is robust against faulty or malicious detectors, reducing the critical detection efficiency needed compared to traditional Bell tests.

Contribution

It proposes an entanglement witness-based approach that overcomes detection loopholes and lowers efficiency thresholds, improving reliability in practical quantum systems.

Findings

Reduces critical detection efficiency compared to Bell tests

Demonstrates robustness against detection loopholes

Applicable to two-qubit Bell states

Abstract

We consider the problem of entanglement detection in the presence of faulty, potentially malicious detectors. A common - and, as of yet, the only - approach to this problem is to perform a Bell test in order to identify nonlocality of the measured entangled state. However, there are two significant drawbacks in this approach: the requirement to exceed a critical, and often high, detection efficiency, and much lower noise tolerance. In this paper, we propose an alternative approach to this problem, which is resilient to the detection loophole and is based on the standard tool of entanglement witness. We discuss how the two main techniques to detection losses, namely the discard and assignment strategies, apply to entanglement witnessing. We demonstrate using the example of a two-qubit Bell state that the critical detection efficiency can be significantly reduced compared to the Bell test approach.