Basis-independent coherence and its distribution in de Sitter spacetime

Abstract: Quantum coherence in curved spacetime offers a fresh window into the interplay between gravity, thermality, and quantum resources. While previous work has shown that Markovian evolution can generate entanglement and other nonclassical correlations in de Sitter backgrounds, the basis-dependent nature of coherence has so far limited its unambiguous interpretation. Here, we introduce a basis-independent framework to quantify not only the total coherence of two comoving detectors, but also its collective and localized contributions, and we trace how each of these decomposed measures varies with the inverse of Gibbons-Hawking temperature. By treating the detectors as open quantum systems interacting with a massless scalar field in the Bunch-Davies and squeezed alpha-vacua, we find that non-thermal squeezing substantially enhances extractable coherence, even under strong thermal effects. Our results demonstrate how basis-independent coherence in de Sitter spacetime can serve as a robust resource for relativistic quantum information protocols.