All quantum mixtures are proper

TL;DR

The paper argues that proper and improper quantum mixed states are indistinguishable observationally, challenging the basis for certain interpretative approaches in quantum mechanics.

Contribution

It demonstrates that proper and improper mixed states cannot be distinguished experimentally, undermining some motivations for relational quantum interpretations.

Findings

Proper and improper mixed states are observationally indistinguishable.

This challenges the basis for relational interpretations of quantum mechanics.

The distinction between mixed states may be unnecessary in quantum theory.

Abstract

It is argued that proper and improper quantum mixed states have no observable differences, and hence should not be distinguished. This has implications for subjective approaches to quantum mechanics, and invalidates one of the main motivations for relational interpretations of QM.