Measurement-device-independent and arbitrarily loss-tolerant verification of quantum steering

TL;DR

This paper introduces a loss-tolerant, measurement-device-independent method to verify quantum steering in two-qubit states, accommodating arbitrary null results and ensuring steerability with non-zero measurement efficiency.

Contribution

It converts a recent steering inequality into a measurement-device-independent criterion that accounts for heralding efficiency and measurement imperfections.

Findings

Steering can be verified with more than 1/η_H measurement settings for entangled states.

Steerability is guaranteed as long as the steered party's measurement efficiency is non-zero.

The method is useful for loss-tolerant and measurement-device-independent quantum steering tasks.

Abstract

We propose a method to verify quantum steering for two qubit states with an arbitrary amount of null results when both the steering and steered parties cannot be trusted. We converted the steering inequality proposed in a recent article [Phys.~Rev.~X {\bf 2}, 031003 (2012)] to a corresponding measurement-device-independent steering criterion that depends on the heralding efficiency of the steering party, number of measurement settings, and imperfection of the state preparation. As a result, for a relative frequency of valid measurement outcomes $\eta_H$, the steering can be verified using a number of different measurement settings larger than $1/\eta_H$ and maximally entangled states. Furthermore, steerability is guaranteed as long as the measurement efficiency of the steered party is non-zero. Our result is useful for loss-tolerant and measurement-device-independent steering tasks.