Quantum superposition of black hole states as a communication resource

The interplay between black holes and quantum information has revealed deep connections between gravity and quantum mechanics. For example, the classical spacetime geometry of a black hole has been shown to degrade quantum entanglement shared by nearby observers, one of whom is in free fall. Here, we examine how this picture changes when the black hole’s mass degrees of freedom are allowed to exist in a coherent quantum superposition, corresponding to a superposition of distinct spacetime geometries. We show that such quantum coherence can mitigate the loss of entanglement between nearby observers, thereby enhancing the performance of quantum communication protocols operating in the vicinity of the black hole. When treated classically, black holes degrade the quantum entanglement shared between nearby observers. The authors find that placing the black hole’s mass - and hence its spacetime - in a quantum superposition can act as a resource to counter this degradation.