A Relationship Between Nonphysical Quasi-probabilities and Nonlocality Objectivity

TL;DR

This paper explores how relaxing the positivity constraint on quantum states' density matrices introduces observer-dependent nonlocality, linking negative quasi-probabilities with nonlocal correlations in quantum systems.

Contribution

It demonstrates that allowing near-negative eigenvalues in density matrices creates states with observer-dependent nonlocality, revealing a connection between nonlocal objectivism and negative quasi-probabilities.

Findings

States with near-negative eigenvalues exhibit observer-dependent nonlocality.

Negative quasi-probabilities are linked to nonlocal correlations.

Nonlocality can depend on the observer's labeling of quantum systems.

Abstract

Density matrices are the most general descriptions of quantum states, covering both pure and mixed states. Positive semidefiniteness is a physical requirement of density matrices, imposing nonnegative probabilities of measuring physical values. Separately, nonlocality is a property shared by some bipartite quantum systems, indicating a correlation of the component parts that cannot be described by local classical variables. In this work, we show that breaking the positive-semidefinite requirement and allowing states with a negative minimal eigenvalue arbitrarily close to zero, allows for the construction of states that are nonlocal under one component labelling but local when the labelling is interchanged. This is an observer-dependent nonlocality, showing the connection between nonlocal objectivism and negative quasi-probabilities.