Giving Operational Meaning to the Superposition of Causal Orders

Understand

In this work, we give rigorous operational meaning to superposition of causal orders.

• This fits within a recent effort to understand how the standard operational perspective on quantum theory could be extended to include indefinite causality.
• The mainstream view, that of "process matrices", takes a top-down approach to the problem, considering all causal correlations that are compatible with local quantum experiments.
• Conversely, we pursue a bottom-up approach, investigating how the concept of indefiniteness emerges from specific characteristics of generic operational theories.