Quantum violation of trivial and non-trivial preparation non-contextuality: Nonlocality and Steering

TL;DR

This paper explores the connection between quantum steering, nonlocality, and preparation contextuality, demonstrating how non-trivial relations between observables lead to new inequalities that unify tests of steering and nonlocality.

Contribution

It introduces a novel link between quantum steering and non-trivial preparation contextuality, deriving new inequalities that connect Bell nonlocality and steering.

Findings

Bell inequalities can be transformed into steering inequalities under non-trivial conditions.

Non-trivial relations between observables can reduce local bounds, enabling unified tests.

The work establishes a direct connection between quantum steering and preparation contextuality.

Abstract

This paper illustrates a direct connection between quantum steering and non-trivial preparation contextuality. In two party-two measurement per party-two outcomes per measurement $(2-2-2)$ Bell scenario, any argument of Bell nonlocality is a proof of trivial preparation contextuality; however, the converse may not hold. If one of the parties (say, Alice) performs the measurements of more than two dichotomic observables, then it is possible to find a set of non-trivial functional relations between Alice's observables. We argue that the existence of a suitable set of such non-trivial relations between Alice's observables may warrant the unsteerability of quantum states at the end of another spatially separated party (say, Bob). Interestingly, such constraints can be read as non-trivial preparation non-contextuality assumptions in an ontological model. We further demonstrate two types of Bell inequalities that can be converted into linear steering inequalities using the aforementioned non-trivial conditions on Alice's observables. Such steering inequalities can also be considered as non-trivial preparation noncontextual inequalities. Since the local bound of the family of Bell expression gets reduced under the additional non-trivial conditions, it provides a test of quantum steering and nonlocality from the same family of Bell expressions depending upon its violation of the non-trivial preparation non-contextual or the local bound, thereby establishing a direct connection between quantum steering and non-trivial preparation contextuality.