Correspondence: Enhancing a phase measurement by sequentially probing a solid state system

TL;DR

This paper critiques a recent claim of entanglement-enhanced phase measurement in a solid-state system, clarifying that the observed enhancement results from a repeated phase application rather than entanglement.

Contribution

The authors clarify that the claimed enhancement in the referenced experiment is due to a double phase application, not entanglement, challenging prior interpretation.

Findings

The enhancement is caused by applying the phase shift twice.

Entanglement was not responsible for the observed improvement.

The critique clarifies the true source of measurement enhancement.

Abstract

In a recent paper, Liu et al. [Nat. Commun. 6:6726 (2015)] claim to perform the first room temperature entanglement-enhanced phase measurement in a solid-state system. We argue here that this claim is incorrect: their measurement is not enhanced because of the entanglement in their system, but instead the enhancement comes from the fact that the phase shift is applied twice to their state.