Abstract
The problem of objectivity, i.e. how to explain on quantum grounds the objective character of the macroscopic world, is one of the aspects of the celebrated quantum-to-classical transition. Initiated by W. H. Zurek and collaborators, this problem gained some attention recently with several approaches being developed. The aim of this work is to compare three of them: quantum Darwinism, Spectrum Broadcast Structures, and strong quantum Darwinism. The paper is concentrated on foundations, providing a synthetic analysis of how the three approaches realize the idea of objectivity and how they are related to each other. As a byproduct of this analysis, a proof of a generalized Spectrum Broadcast Structure theorem is presented. Recent quantum Darwinism experiments are also briefly discussed.
Highlights
The fact that classical limit of quantum theory should reproduce the correct kinematics and dynamics of classical theory, but on a deeper level its objective character, has been noted fairly late, at least to the author’s knowledge, by W
We find that the evolution US:E = e−itH is of so called controlled-unitary type, where the state of the central system controls which unitary is applied to the environment: N
The authors clearly state that they focus only on χ( f E|S), as the remaining part of the quantum mutual information - the discord, involves non-local correlations which do not help in establishing objectivity
Summary
The fact that classical limit of quantum theory should reproduce the correct kinematics and dynamics of classical theory, but on a deeper level its objective character, has been noted fairly late, at least to the author’s knowledge, by W. Quantum measurements inevitably perturb measured system, unless the state of the system is specially tailored for a given measurement, precluding in general any objective character of the measured quantity as different observations will yield different results. This is in a stark contrast to classical mechanics, where system’s characteristics, e.g. positions or momenta, have an objective, observer-independent character. Every real-life system is immersed in some sort of environment and most of our everyday observations are indirect, mediated by the environment This is the key difference between the objectivity studies and the standard quantum open systems theory [7].
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