  We study, in the framework of open quantum systems, the entanglement
generation between two mutually independent static two-level atoms in de Sitter
spacetime. We treat the two-atom system as an open system in interaction with a
bath of fluctuating conformally coupled massless scalar fields in the de Sitter
invariant vacuum and derive the master equation which governs its evolution.
With the help of the partial transposition criterion, we analyze entanglement
generation between the two initially separable atoms and find that static atoms
in de Sitter spacetime exhibit distinct characteristics from those in a thermal
bath in flat spacetime in terms of entanglement generation. So, in, principle,
one can tell whether he is in a thermal bath or in de Sitter space by checking
the entanglement creation between two initially separable static atoms in
certain circumstances.
