The evolution of expanding spacetime realizes approximate quantum cloning

Abstract

We investigate how quantum information, encoded in a quantum field, evolves during the expansion of spacetime. Due to information loss across the horizon, a local observer experiences this evolution as a nonunitary quantum channel. We obtain this channel in the case of de Sitter spacetime by assuming the initial global state encodes a signal state via fluctuations of the Bunch-Davies vacuum. Notably, de Sitter evolution exhibits intriguing cloning properties, establishing a connection between the curvature of spacetime and the propagation of quantum information.