Entangled Unruh-DeWitt detectors amplify quantum coherence

TL;DR

This paper demonstrates that nonperturbative interactions of entangled Unruh-DeWitt detectors with a quantum field can amplify quantum coherence while reducing entanglement, revealing a dual behavior contrasting previous perturbative studies.

Contribution

It introduces a nonperturbative analysis showing that quantum coherence can be amplified independently of entanglement degradation in detector-field interactions.

Findings

Increasing coupling strength enhances quantum coherence.

Entanglement decreases monotonically with coupling.

Separable detectors can harvest quantum coherence from the vacuum.

Abstract

We explore the quantum coherence between a pair of entangled Unruh-DeWitt detectors, interacting with a quantum field, using a nonperturbative approach in a (3+1)-dimensional Minkowski spacetime with instantaneous switching ($\delta$-switching). It is intriguing to observe that for a maximally entangled state, increasing the coupling strength enhances the detectors' initial quantum coherence while simultaneously causing a monotonic decrease in their initial entanglement. This reveals a remarkable phenomenon: through nonperturbative interactions, entangled Unruh-DeWitt detectors can exhibit a dual effect-amplifying quantum coherence while degrading quantum entanglement. This finding stands in stark contrast to previous studies based on perturbative methods or Gaussian switching functions, which generally concluded that interactions between detectors and the field lead to a simultaneous degradation of quantum coherence and entanglement due to environmental decoherence. Notably, while initially separable detectors successfully harvest quantum coherence from the vacuum, entanglement extraction remains fundamentally prohibited. These contrasting behaviors underscore the fundamental distinction between coherence and entanglement as quantum resources, and highlight their complementary roles in field-detector interactions.