Masanes-Galley-M\"uller and the State-Update Postulate

TL;DR

This paper critically examines the derivation of a quantum state update rule by Masanes, Galley, and Müller, revealing that their proof assumes linearity, which is a key implicit step.

Contribution

The paper provides a critical analysis showing that the derivation of the quantum state update rule relies on an unproven assumption of linearity.

Findings

The proof implicitly assumes linearity of the state-update rule.

Linearity assumption is not justified within the original proof.

The critique questions the uniqueness of the derived rule.

Abstract

Masanes, Galley and M\"uller claim to have derived a unique rule for quantum state update consequent upon a measurement outcome. Upon closer examination, their proof implicitly assumes its first step, namely that the state-update rule is linear.