Alice falls into a black hole: entanglement in noninertial frames.

TLDR: It is shown that a state which is maximally entangled in an inertial frame becomes less entangled if the observers are relatively accelerated, which shows that entanglement is an observer-dependent quantity in noninertial frames.

Abstract: 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 noninertial frames. In the high acceleration limit, our results can be applied to a nonaccelerated 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.