Entanglement harvesting between Unruh DeWitt detectors in the de Sitter spacetime

We investigate the generation and harvesting of entanglement between two identical, comoving Unruh–DeWitt detectors in cosmological de Sitter spacetime. Initially, the detectors are unentangled and interact locally with a complex scalar field, through which an effective coupling between them emerges. Our analysis considers two types of complex scalar fields, the conformally invariant field and the massless minimally coupled field, both of which exhibit distinct physical behaviours in curved spacetime. By tracing out the scalar-field degrees of freedom, we construct the reduced density matrix of the detector pair. The eigenvalues of this matrix encode the transition probabilities between the energy levels of the detectors and allow us to compute the negativity, which serves as a quantitative measure of the entanglement generated at late times.

We present a detailed comparison of the entanglement-harvesting capabilities of the two complex fields, highlighting both their similarities and their qualitative differences. To place our findings in context, we also contrast them with the well-studied case of a real scalar field. Our results show that complex fields and nonlinear couplings significantly enhance the robustness of entanglement harvesting, allowing entanglement to persist over a broader parameter range. This indicates that the structure of the underlying field theory plays a crucial role in determining the efficiency of entanglement generation in curved spacetime.