Mixed-state entanglement in noninertial frames

The entanglement between two modes of a free scalar field (or a free Dirac field) is investigated in noninertial frames under the condition that they are initially prepared in a Werner state. It is found that the entanglement degradation induced by the Unruh effect highly depends on the initial purity f and the type of fields. For a fixed acceleration r, the critical values of f for the states entangled or separable are obtained in both scalar and Dirac fields. Finally, we make a comparison between the entanglement and the quantum discord and show that quantum discord is more robust than entanglement in our models.