Revisiting quantum information flow in black hole evaporation

We revisit Hawking's black hole radiation derivation, including the quantum state of the initial matter forming the black hole. We investigate how non-vacuum initial quantum states, at the past of a black hole geometry, influence the black hole radiation observed at future null infinity. We further classify which of the initial state excitations are distinguishable from one another through measurements on the black hole radiation state. We discuss the cases of a collapsing black hole and a collapsing black hole that is evaporating. We model the black hole collapsing matter as excitations of the scalar quantum field. We use Algebraic Quantum Field Theory to provide a clear physical interpretation of the results, in terms of localised operations.

In a concrete example of a black hole made of one large collapsing excitation of mass M, and compare it to a same-mass black hole formed due to the collapse of two smaller excitations, of mass M/2 each. We find using our formalism that the two cases yield different non-thermal radiation states and can, in principle, be distinguished.Our results provide a mechanism for partial information recovery in collapsing black holes, and total information recovery in fully evaporated black hole geometries that do not form singularities.