Quantum Recovery from Black-Hole Radiation Beyond the Emission Yield

Abstract

A proposed resolution of the black-hole information paradox must explain which information an outside observer can recover from escaping radiation\cite{Hawking,Page,Hayden,Almheiri}. Environmental memory can return correlations to the source without delivering them to that observer\cite{ChenQi,ChenMemory}. Here we establish a sharp recovery frontier at fixed mean radiation yield for single-excitation channels and realize its qubit limit with an autonomous quantum-memory emitter. Unequal transmissions balance retained coherence against information in failed collection events. A reference--radiation correlation test distinguishes this gain even when the mean collected energy is unchanged. Identical transmission channels instead give the same recovery at matched collection, regardless of their emission timescales. For a broader class of interacting sources, an ordering of collected and inaccessible coupling spectra forbids unassisted quantum transmission irrespective of internal memory. A separate coding example supports a positive rate where uniform transmission at matched actual yield has zero capacity. Together, these results identify what openness must change to assist recovery: the accessible transmission structure. They supply a physically constrained comparison of evaporation mechanisms, separating information delivered to radiation from coherence retained elsewhere or an increase in the collected output.