# Communication games reveal preparation contextuality

## TL;DR

This paper demonstrates that communication games can reveal the preparation contextuality of physical theories, including all mixed quantum states, through theoretical analysis and experimental validation.

## Contribution

It establishes a direct link between communication game statistics and preparation contextuality, and experimentally shows violation of noncontextuality constraints in quantum systems.

## Key findings

- All mixed quantum states are preparation contextual.
- Communication game statistics correspond to no-signaling correlations.
- Experimental violation of preparation noncontextuality constraints.

## Abstract

A communication game consists of distributed parties attempting to jointly complete a task with restricted communication. Such games are useful tools for studying limitations of physical theories. A theory exhibits preparation contextuality whenever its predictions cannot be explained by a preparation noncontextual model. Here, we show that communication games performed in operational theories reveal the preparation contextuality of that theory. For statistics obtained in a particular family of communication games, we show a direct correspondance with correlations in space-like separated events obeying the no-signaling principle. Using this, we prove that all mixed quantum states of any finite dimension are preparation contextual. We report on an experimental realization of a communication game involving three-level quantum systems from which we observe a strong violation of the constraints of preparation noncontextuality.