Branching States as The Emergent Structure of a Quantum Universe

ABSTRACT: Quantum Darwinism builds on decoherence theory to explain the emergence of classical behavior within a quantum universe. We demonstrate that the differential geometric underpinnings of quantum mechanics provide a uniquely informative window into the structure of correlations needed to validate Quantum Darwinism. This leads us to two crucial insights about the emergence of classical phenomenology, centered around the nullity of quantum discord. First, we show that the so-called branching structure of the joint state of system and environment is the only one compatible with zero discord. Second, we prove that for small, but nonzero discord, the structure of the globally pure state is arbitrarily close to the branching form. These provide strong evidence that this class of branching states is the only one compatible with the emergence of classical phenomenology, as described in Quantum Darwinism.