New Insights into Quantum Processes and Relativistic Causality

Recent research by V. Vilasini and Renato Renner, titled "Fundamental limits for realising quantum processes in spacetime," explores the boundaries of quantum processes as they relate to classical spacetime. The authors derive no-go theorems that highlight limitations on quantum experiments that can be conducted within classical backgrounds. This work builds on Bell's no-go theorem, which outlines constraints on classical processes due to relativistic causality principles.

The first theorem presented indicates that implementations of indefinite causal order (ICO) processes, which have gained attention in recent experiments, must involve the non-localization of systems in spacetime if they are to adhere to relativistic causality. The second theorem posits that any realization of an ICO process can be described in terms of a more detailed and acyclic causal order process. This finding reconciles quantum and relativistic notions of causality, particularly in relation to experimental setups like the quantum switch, a notable ICO process.

These results not only delineate what cannot be achieved in classical spacetimes but also provide insights into how causality and information processing may diverge in future quantum experiments conducted in relativistic environments. The implications of this research could significantly influence the design and understanding of quantum experiments that operate under relativistic conditions, thereby advancing the field of quantum physics further into the realm of practical applications.

The full paper can be accessed at arXiv:2408.13387.