A quantum state is said to be objective if multiple observers are able to recover information about the state and agree among themselves. This is in turn possible only if said information was encoded multiple times into the surrounding environment. In this paper, we show how it is not always possible for the observers to extract all of the relevant information that was initially encoded into the environment. We do this by introducing two quantities with a rigorous definition and a clear operative interpretation: “redundancy”, which quantifies how many times the information was written into the environment, and “consensus”, which is the maximum number of observers able to extract said information.
D.A. Chisholm, L. Innocenti, G.M. Palma, Quantum 7, 1074 (2023)
Link to the article: “https://quantum-journal.org/papers/q-2023-08-03-1074/”