Amplification, Redundancy, and Quantum Chernoff Information

This is the publisher’s final pdf. The published article is copyrighted by the American Physical Society and can be found at: http://journals.aps.org/prl/.Amplification was regarded, since the early days of quantum theory, as a mysterious ingredient that\ud endows quantum microstates with macroscopic consequences, key to the “collapse of the wave packet,”\ud and a way to avoid embarrassing problems exemplified by Schrödinger’s cat. Such a bridge between the\ud quantum microworld and the classical world of our experience was postulated ad hoc in the Copenhagen\ud interpretation. Quantum Darwinism views amplification as replication, in many copies, of the information\ud about quantum states. We show that such amplification is a natural consequence of a broad class of models\ud of decoherence, including the photon environment we use to obtain most of our information. This leads\ud to objective reality via the presence of robust and widely accessible records of selected quantum states.\ud The resulting redundancy (the number of copies deposited in the environment) follows from the quantum\ud Chernoff information that quantifies the information transmitted by a typical elementary subsystem of the\ud environment