Realism-based nonlocality: Invariance under local unitary operations and asymptotic decay for thermal correlated states

TL;DR

This paper investigates the properties of realism-based nonlocality (RBN), proving its invariance under local unitary operations, analyzing its decay under quantum noise, and exploring its potential in quantum communication security.

Contribution

It provides an analytical proof of RBN's invariance, studies its behavior under noise and thermal states, and compares it with quantum discord, highlighting its robustness and application potential.

Findings

RBN is invariant under local unitary operations.

RBN decays asymptotically with temperature in thermal states.

RBN can detect nonlocal features even without quantum discord.

Abstract

The realism-based nonlocality (RBN) is a recently introduced measure that differs from the well-known Bell's nonlocality. For bipartite states, the RBN concerns how much an element of reality associated with a given observable is affected upon local measurements on a subsystem. Here, we present an analytical proof for the unitary invariance of the RBN and that it presents a monotonous behavior upon the action of unital and non-unital local quantum noise. We illustrate our results by employing the two-qubits Werner state and thermal quantum correlated states. We show how the RBN is limited by the initial equilibrium temperature and, especially, that it decays asymptotically with it. These results also corroborate the hierarchy relationship between the quantifiers of RBN and global quantum discord, showing that RBN can capture undetectable nonlocal aspects even for non-discordant states. Finally, we argue how our results can be employed to use the RBN as a security tool in quantum communication tasks.