Negative entropy in scrambling black holes

We present a microscopic statistical-mechanical foundation for interpreting the horizon area of a scrambling black hole as coherent information, equivalently negative conditional quantum entropy, in Hawking's pair-creation picture. We derive the entropy increase induced in a black hole when an infalling object is absorbed and scrambled into its microscopic degrees of freedom. Up to finite-reservoir corrections, this increase takes a canonical form at the Hawking temperature, regardless of the initial entropy carried by the infalling object. Applying this entropy formula to an incoming mode paired by time reversal with an outgoing Hawking radiation mode, we show that their partition-function contributions cancel in the coherent-information balance associated with the horizon area. The resulting area response is then determined only by the energy flux, in agreement with the black-hole first law.