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The meaning of redundancy and consensus in quantum objectivity

Quantum 7, 1074 (2023)

D.A. Chisholm, L. Innocenti, G.M. Palma

While the terms “redundancy” and “consensus” are often used as synonyms in the context of quantum objectivity, we show here that these should be understood as two related but distinct notions, that quantify different features of the quantum-toclassical transition. We show that the two main frameworks used to measure quantum objectivity, namely spectrum broadcast structure and quantum Darwinism, are best suited to quantify redundancy and consensus, respectively. Furthermore, by analyzing explicit examples of states with nonlocally encoded information, we highlight the potentially stark difference between the degrees of redundancy and consensus. In particular, this causes a break in the hierarchical relations between spectrum broadcast structure and quantum Darwinism. Our framework provides a new perspective to interpret known and future results in the context of quantum objectivity, paving the way for a deeper understanding of the emergence of classicality from the quantum realm.

Project manager
Irene Spagnul
Department of Physics
University of Trieste


Co-funded by the European Commission’s
Horizon Europe Programme under GA 101046973

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