Qubit models of black hole evaporation

Recently, several simple quantum mechanical toy models of black hole evaporation have appeared in the literature attempting to illuminate the black hole information paradox. We present a general class of models that is large enough to describe both unitary and nonunitary evaporation, and study a few specific examples to clarify some potential confusions regarding recent results. We also generalize Mathur's bound on small corrections to black hole dynamics. Conclusions are then drawn about the requirements for unitary evaporation of black holes in this class of models. We present a one-parameter family of models that continuously deforms nonunitary Hawking evaporation into a unitary process. The required deformation is large.