When entanglement harvesting is not really harvesting

TL;DR

This paper investigates the entanglement harvesting protocol in scenarios where detectors are in causal contact, revealing that genuine harvesting occurs only when detectors cannot communicate via the field, especially in massless fields.

Contribution

The study introduces a quantitative estimator to distinguish between entanglement from communication and genuine harvesting, clarifying the conditions under which true entanglement harvesting occurs.

Findings

Entanglement in causally connected detectors often results from communication, not genuine harvesting.

Massive fields allow genuine harvesting alongside communication.

In massless fields, communication dominates entanglement generation, not harvesting.

Abstract

We revisit the entanglement harvesting protocol when two detectors are in causal contact. We study the role of field-mediated communication in generating entanglement between the two detectors interacting with a quantum field. We provide a quantitative estimator of the relative contribution of communication versus genuine entanglement harvesting. For massless scalar fields in flat spacetime, we show that when two detectors can communicate via the field, the detectors do not really harvest entanglement from the field, and instead they get entangled only via the field-mediated communication channel. In other words, in these scenarios the entanglement harvesting protocol is truly "harvesting entanglement" from the field only when the detectors are not able to communicate. In contrast, for massive scalar fields both communication and genuine harvesting contribute equally to the bipartite entanglement when the detectors are causally connected. These results emphasize the importance of taking into account the causal relationships between two parties involved in this relativistic quantum information protocol before we can declare that it is truly entanglement harvesting.