Two observers determine the entanglement between two free bosonic modes by each detecting one of the modes and observing the correlations between their measurements. We show that a state which is maximally entangled in an inertial frame becomes less entangled if the observers are relatively accelerated. This phenomenon, which is a consequence of the Unruh effect, shows that entanglement is an observer-dependent quantity in non-inertial frames. In the high acceleration limit, our results can be applied to a non-accelerated observer falling into a black hole while the accelerated one barely escapes. If the observer escapes with infinite acceleration, the state's distillable entanglement vanishes. Entanglement is a property of multipartite quantum states that arises from the tensor product structure of the Hilbert space and the superposition principle. It is considered to be a resource for quantum information tasks such as teleportation [1] and has applications in quantum control [2] and quantum simulations [3]. Non-relativistic bipartite entanglement can be quantified uniquely for pure states by the von Neumann entropy and for mixed states several measures have been proposed such as entanglement cost, distillable entanglement and logarithmic negativity [4]. Understanding entanglement in the relativistic framework is crucial from both fundamental and practical perspectives. Relativistic space-time presents naturally a more complete setting for theoretical considerations and many experimental set-ups require such a treatment. This program is therefore an important and topical one. It is only in this framework that we can understand quantum information tasks involving entanglement between moving observers. A central question in the field of relativistic quantum information is whether entanglement is observer-independent. So far, it has been shown that entanglement between inertial moving parties remains constant although the entanglement between some degrees of freedom can be transferred to others [5].In this letter we investigate the entanglement between two modes of a non-interacting massless scalar field when one of the observers describing the state is uniformly accelerated. We consider a maximally entangled pure state in an inertial frame and describe its entanglement from a non-inertial perspective. Our results imply that only inertial observers in flat spacetime agree on the degree of entanglement, whereas non-inertial observers see a degradation. While Minkowski coordinates (t, z) are the most suitable to describe the field from an inertial perspective, * Published before under name Fuentes-Guridi Rindler coordinates (τ, ξ) are appropriate for discussing the viewpoint of an observer moving with uniform acceleration. Two different sets of Rindler coordinates, which differ from each other by a sign change in the temporal coordinate, are necessary for covering Minkowski space. These sets of coordinates define two Rindler regions that are causally disconnected from each other. A particle undergoing uniform accele...

We analyze the entanglement between two modes of a free Dirac field as seen by two relatively accelerated parties. The entanglement is degraded by the Unruh effect and asymptotically reaches a non-vanishing minimum value in the infinite acceleration limit. This means that the state always remains entangled to a degree and can be used in quantum information tasks, such as teleportation, between parties in relative uniform acceleration. We analyze our results from the point of view afforded by the phenomenon of entanglement sharing and in terms of recent results in the area of multi-qubit complementarity.

We study the distribution of entanglement between modes of a free scalar field from the perspective of observers in uniform acceleration. We consider a two-mode squeezed state of the field from an inertial perspective, and analytically study the degradation of entanglement due to the Unruh effect, in the cases of either one or both observers undergoing uniform acceleration. We find that for two observers undergoing finite acceleration, the entanglement vanishes between the lowest frequency modes. The loss of entanglement is precisely explained as a redistribution of the inertial entanglement into multipartite quantum correlations among accessible and unaccessible modes from a non-inertial perspective. We show that classical correlations are also lost from the perspective of two accelerated observers but conserved if one of the observers remains inertial.