Universal structure of objective states in all fundamental causal theories

TL;DR

This paper introduces a universal framework for understanding how objective states emerge across all fundamental causal theories, revealing that spectrum broadcast structure universally characterizes objective states despite diverse decoherence behaviors.

Contribution

It defines a universal decoherence process applicable to all causal theories and proves the spectrum broadcast structure's universal role in objective states.

Findings

Decoherence behavior varies greatly across theories.

Spectrum broadcast structure universally characterizes objective states.

Objective states exhibit a universal structure despite diverse decoherence dynamics.

Abstract

A crucial question is how objective and classical behavior arises from a fundamental physical theory. Here we provide a natural definition of a decoherence process valid in all causal theories, and show how its behavior can be extremely different from the quantum one. Remarkably, despite this, we prove that the so-called spectrum broadcast structure characterizes all objective states in every fundamental causal theory, exactly as in quantum mechanics. Our results show a stark contrast between the extraordinarily diverse decoherence behavior and the universal features of objectivity.