Composition of multipartite quantum systems: perspective from time-like paradigm

TL;DR

This paper explores how different composition rules for quantum systems can lead to stronger time-like correlations than quantum mechanics predicts, suggesting new ways to understand quantum foundations and test quantum composition.

Contribution

It introduces a framework where bipartite quantum systems can exhibit stronger time-like correlations, challenging the traditional quantum composition paradigm.

Findings

Bipartite compositions can admit stronger than quantum time-like correlations.

Different composition rules imply distinct roles for state and effect cones.

Potential for experimental tests of quantum composition rules.

Abstract

Figuring out the physical rationale behind natural selection of quantum theory is one of the most acclaimed quests in quantum foundational research. This pursuit has inspired several axiomatic initiatives to derive mathematical formulation of the theory by identifying general structure of state and effect space of individual systems as well as specifying their composition rules. This generic framework can allow several consistent composition rules for a multipartite system even when state and effect cones of individual subsystems are assumed to be quantum. Nevertheless, for any bipartite system, none of these compositions allows beyond quantum space-like correlations. In this letter we show that such bipartite compositions can admit stronger than quantum correlations in the time-like domain and, hence, indicates pragmatically distinct roles carried out by state and effect cones. We discuss consequences of such correlations in a communication task, which accordingly opens up a possibility of testing the actual composition between elementary quanta.