Degradation of nonmaximal entanglement of scalar and Dirac fields in noninertial frames

The entanglement between two modes of free scalar and Dirac fields as seen by two relatively accelerated observers has been investigated. It is found that the same initial entanglement for an initial state parameter alpha and its "normalized partner" root 1-alpha(2) will be degraded by the Unruh effect along two different trajectories except for the maximally entangled state, which just shows the inequivalence of the quantization for a free field in Minkowski and Rindler coordinates. In the infinite-acceleration limit, the state does not have distillable entanglement for any alpha for the scalar field, but always remains entangled to a degree that is dependent on alpha for the Dirac field. It is also interesting to note that in this limit the mutual information equals just half of the initial mutual information; this result is independent of alpha and the type of field.