Quantum Physics

Causality is a core concept in both General Relativity (GR) and Quantum Information Theory (QIT), yet it manifests differently in each domain. In GR, causal cones appear as a defining property of spacetime. Conversely, in QIT, causality relates to the abstract flow of information in quantum processes, independent of spacetime. This raises a crucial question: under what conditions can an abstract quantum process be realised within spacetime? The question is especially intriguing for quantum processes with indefinite causal structure, like the Quantum Switch, which resist classical causal descriptions. In this talk, I will present no-go theorems that reveal fundamental limitations on the realisability of such processes in spacetime and, thus, more generally, on the interplay between GR and QIT. This is based on joint work with V. Vilasini (Physical Review Letters, 133 080201, 2024).