Maria Papageorgio (Vienna): Local operations in Quantum Field Theory: rethinking relativistic causality

Recent developments in local measurement theory for Quantum Field Theory (QFT) offer new perspectives on relativistic causality. The representation of dynamics in such theories imposes crucial constraints on local (rather than asymptotic) quantum measurements and their signalling properties. Sorkin's 'impossible measurements' scenario demonstrates that microcausality alone is insufficient to prevent superluminal signalling in relativistic quantum theories employing Lüders' state update rule. This raises fundamental questions about local operations and their interpretation in QFT.
In this talk, we examine how recently developed measurement theories—particularly detector-based approaches and the Fewster-Verch framework in algebraic QFT—address these challenges. We adopt the local S-matrix formalism and utilise a hierarchy of factorisation conditions that exclude superluminal signalling and retrocausality. These conditions provide a criterion for local quantum operations that are causal and, thus, physically implementable.