# Entanglement harvesting and divergences in quadratic Unruh-DeWitt detectors pairs

## TL;DR

This paper investigates the entanglement harvesting process using quadratic Unruh-DeWitt detectors, revealing persistent divergences in detector pairs and proposing a UV-safe measure for correlations, with implications for fermionic vacuum studies.

## Contribution

It uncovers unanticipated divergences in entanglement harvesting with quadratic detectors and introduces a UV-safe correlation measure, advancing understanding of detector-field interactions.

## Key findings

- Single quadratic detectors show no divergences.
- Detector pairs exhibit persistent divergences in harvested entanglement.
- A UV-safe quantifier for correlations is proposed.

## Abstract

We analyze correlations between pairs of particle detectors quadratically coupled to a real scalar field. We find that, while a single quadratically coupled detector presents no divergences, when one considers pairs of detectors there emerge unanticipated persistent divergences (not regularizable via smooth switching or smearing) in the entanglement they acquire from the field. We have characterized such divergences, discussed whether a suitable regularization can allow for fair comparison of the entanglement harvesting ability of the quadratic and the linear couplings, and finally we have found a UV-safe quantifier of harvested correlations. Our results are relevant to future studies of the entanglement structure of the fermionic vacuum.