Strong Quantum Darwinism and Strong Independence is equivalent to Spectrum Broadcast Structure

TL;DR

This paper demonstrates that strong quantum Darwinism combined with strong independence is equivalent to spectrum broadcast structure, clarifying the conditions under which quantum systems exhibit objective classical states.

Contribution

It introduces strong quantum Darwinism, proves its equivalence to spectrum broadcast structure with strong independence, and shows its necessity and sufficiency for state objectivity.

Findings

Strong quantum Darwinism is equivalent to spectrum broadcast structure with strong independence.

Strong quantum Darwinism alone is sufficient and necessary for state objectivity.

The work advances understanding of the quantum-to-classical transition.

Abstract

How the objective everyday world emerges from the underlying quantum behaviour of its microscopic constituents is an open question at the heart of the foundations of quantum mechanics. Quantum Darwinism and spectrum broadcast structure are two different frameworks providing key insight into this question. Recent works, however, indicate these two frameworks can lead to conflicting predictions on the objectivity of the state of a system interacting with an environment. Here we provide a resolution to this issue by defining strong quantum Darwinism and proving that it is equivalent to spectrum broadcast structure when combined with strong independence of the subenvironments. We further show that strong quantum Darwinism is sufficient and necessary to signal state objectivity without the requirement of strong independence. Our work unveils the deep connection between strong quantum Darwinism and spectrum broadcast structure, thereby making fundamental progress towards understanding and solving the emergence of classicality from the quantum world. Together they provide us a sharper understanding of the transition in terms of state structure, geometry, and quantum and classical information.