Title: Eavesdropping on the Decohering Environment: Quantum Darwinism, Amplification, and the Origin of Objective Classical Reality
Authors: Akram Touil, Bin Yan, Davide Girolami, Sebastian Deffner, and Wojciech Hubert Zurek
Phys. Rev. Lett. 128, 010401 – Published 6 January 2022
“How much information about a system can one extract from a fragment of the environment E that decohered it?” is the central question of Quantum Darwinism. To date, most answers relied on the quantum mutual information of SF, or on the Holevo bound on the channel capacity of F to communicate the classical information encoded in S. These are reasonable upper bounds on what is really needed but much harder to calculate—the accessible information in the fragment F about S. We consider a model based on imperfect C-NOT gates where all the above can be computed, and discuss its implications for the emergence of objective classical reality. We find that all relevant quantities, such as the quantum mutual information as well as various bounds on the accessible information exhibit similar behavior. In the regime relevant for the emergence of objective classical reality this includes scaling independent of the quality of the imperfect C-NOT gates or the size of E, and even nearly independent of the initial state of S.
One of the major open problems in physics is the emergence of classicality from underlying quantum principles. These seemingly peculiar principles are directly at odds with our classical intuition since they are absent in our familiar physical reality. However, within the framework of Quantum Darwinism, the well-studied features of quantum mechanics such as superposition and entanglement are the building blocks of nature that explain and account for our classical everyday observations, hence our perception of classicality.
The present manuscript studies the emergence of classicality from within our quantum universe, relying on the insights of Quantum Darwinism. Within this framework, the general setup consists of a quantum system S interacting with its environment E composed of fragments F. The system-environment interaction leads to redundant imprinting of classical information, about the system of interest S, in different fragments F of the environment. Quantum Darwinism recognizes that our classical perception within the quantum universe is a result of the indirect nature of our observations. In other words, we perceive the classical world around us by eavesdropping on environmental fragments F reflecting information about a few selected (classical) states. Therefore, the main question in Quantum Darwinism, which is addressed in this work, is “How much information about a system can one extract from a fragment of the environment that decohered it?”. Moreover, the analytic results of the present analysis extend to the photon scattering model, which suggests that this analysis captures universal attributes in cases when decoherence is caused by environments composed of noninteracting subsystems such as photons. Therefore, the present work opens a new avenue of research that can be pursued in other settings within the framework of Quantum Darwinism.
Posted: January 6, 2022, 10:25 PM