Relative descriptors for quantum agents

Abstract: We use the Heisenberg picture of Everettian quantum mechanics to work out the relative descriptors for the Frauchiger-Renner thought experiment. While Everettian mechanics reveals no paradox within the thought experiment, the decoherence-free setup offers an instructive branching tree. Traditionally, branching structures derived from the Schr\"odinger picture suggest that foliations are always sharply defined. However, the Heisenberg picture demonstrates that the tree contains regions with inherently non-sharp foliations, leading to the conclusion that, in Everettian mechanics, quantum agents possess a history with a non-sharp memory registry.