  We investigate entanglement of a quantum field in de Sitter spacetime using a
particle detector model. By considering the entanglement between two comoving
detectors interacting with a scalar field, it is possible to detect the
entanglement of the scalar field by swapping it to detectors. For the massless
minimal scalar field, we find that the entanglement between the detectors
cannot be detected when their physical separation exceeds the Hubble horizon
scale. This behavior supports the appearance of the classical nature of quantum
fluctuations generated during the inflationary era.
