MG15 - Talk detail

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Abstract

We study the quantum communication between two observers located close to a non-rotating Black Hole. The communication signal is exchanged by means of a massless quantum scalar field. Each observer has a Unruh-DeWitt particle detector: a two-level system that couples to the scalar field. In order for the receiver (Bob) to extract any information that the sender (Alice) has sent, it is necessary to compute the retarded Green function for scalar field perturbations of the Schwarzschild metric. The first scenario that we study corresponds to the case when Alice and Bob are at fixed spatial positions with zero angular separation. We find that the direct-null-geodesic contribution to the probability of Bob guessing the information that Alice sent via the quantum channel is equal to 1/2 plus an amount which is proportional to the inverse of the radial separation between detectors. We also calculate the contribution to information transmission from geodesics that orbit around the black hole. Finally, we consider the particularly interesting case where the detectors are at caustics, thus enhancing information transmission.

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