Roads to objectivity: Quantum Darwinism, Spectrum Broadcast Structures, and Strong quantum Darwinism – a review

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.

Correlations, Information Backflow, and Objectivity in a Class of Pure Dephasing Models

“…As discussed in detail in many publications [ 6 , 23 , 24 , 25 , 40 , 41 , 42 , 43 , 44 ], this feature might have an impact on the notion of objectivity for a quantum state, in the spirit of so-called quantum Darwinism [ 3 ] (see, for example, ref. [ 7 ] for a recent review and references therein). We see that it also provides us with interesting insights in the study of quantum non-Markovianity [ 8 , 9 ].…”

“…We use both as quantifiers of bipartite correlations by renormalizing to the value assumed for the case of a maximally entangled state. The choice of the QJSD is motivated by its use in the framework of non-Markovianity [ 45 , 46 ], while the relative entropy is typically used in the framework of quantum Darwinism [ 7 ] due to its connection with the mutual information.…”

“…It is to be stressed that the mutual information provides the standard choice of a correlation quantifier in this framework, though others were also considered [ 40 , 44 ]. This notion of objectivity is not uncontroversial; see [ 7 ] for a critical discussion and further developments. The formation of the plateau is slowed down with decreasing c , while for , such that the environmental units are maximally mixed, correlations are only established between the system and the environment as a whole.…”

“…Reverting to a full microscopic description, where the system and environment interact and evolve according to an overall unitary dynamics, reveals that the correlations established between the system and the environment during their interaction play an important role in the resulting open dynamics of the system [ 1 , 2 ]. These correlations are the basis for notions of classical objectivity [ 3 , 4 , 5 , 6 , 7 ] and are also known to play a key role in the characterisation of the dynamics, in particular, if the system undergoes a Markovian (memoryless) or non-Markovian evolution [ 8 , 9 ]. Both notions of classical objectivity and non-Markovian evolution have been the object of experimental investigations; see, for example, [ 10 , 11 , 12 , 13 ] and [ 14 , 15 , 16 , 17 , 18 , 19 , 20 ], respectively.…”

Correlations, information backflow, and objectivity in a class of pure dephasing models

“…Reverting to a full microscopic description, where the system and environment interact and evolve according to an overall unitary dynamics, reveals that the correlations established between the system and the environment during their interaction play an important role in the resulting open dynamics of the system [1,2]. These correlations are the basis for notions of classical objectivity [3][4][5][6][7] and are also known to play a key role in the characterisation of the dynamics, in particular, if the system undergoes a Markovian (memoryless) or non-Markovian evolution [8,9]. Both notions of classical objectivity and non-Markovian evolution have been the object of experimental investigations, see for example [10][11][12][13] and [14][15][16][17][18][19][20] respectively.…”