Measurements in QFT: Weakly coupled local particle detectors and entanglement harvesting

TL;DR

This paper compares AQFT-based frameworks with Unruh-DeWitt models to clarify whether weakly coupled local detectors can harvest vacuum entanglement, concluding that realistic detectors are not hindered by mixedness effects.

Contribution

It demonstrates that the mixedness of local particle detectors is negligible at realistic scales, allowing entanglement harvesting contrary to previous claims.

Findings

Weakly coupled detectors can harvest vacuum entanglement.

Mixedness effects are negligible at realistic localization scales.

Reeh-Schlieder theorem does not prevent entanglement harvesting.

Abstract

We present a comparison of the AQFT-based Fewster-Verch framework with the Unruh-DeWitt particle detector models commonly employed in relativistic quantum information and QFT in curved space. We use this comparison to respond to a recent paper [arXiv:2103.13400] in which it was argued that the Reeh-Schlieder theorem prevents weakly coupled local particle detectors from harvesting vacuum entanglement from a quantum field. Their claim can be traced back to the mixedness that a local particle detector cannot escape from because of the entanglement that it must have with the quantum fields outside of the localization area. We argue that for any realistic scale of localization for physical particle detectors the effect of that mixedness is negligible, and that weakly coupled localized particle detectors are not impeded from harvesting vacuum entanglement.