Factorization conditions and causality for local measurements in QFT
Year: 2026
Type: article
Abstract: Quantum operations that are perfectly admissible in nonrelativistic quantum theory can enable signaling between spacelike separated regions when naively imported into quantum field theory (QFT). Prominent examples of such “impossible measurements” include certain unitary kicks and projective measurements. It is generally accepted that only those quantum operations whose physical implementation arises from a fully relativistically covariant interaction, between the quantum field and a suitable probe, should be regarded as admissible. While this idea has been realized at the level of abstract algebraic QFT, or via particular measurement models, there is still no general set of operational criteria characterizing which measurements are physically implementable. In this work we adopt the local S -matrix formalism to describe local operations, and make use of a hierarchy of factorization conditions that exclude both superluminal signaling and retrocausality, thereby providing such a criterion. Realizing the local S -matrices through explicit interactions between smeared field operators and a pointer degree of freedom, we further derive local causality conditions for the induced Kraus operators, which guarantee the absence of signaling in “impossible measurement” scenarios. Finally, we show that the accuracy with which local field observables can be measured is fundamentally limited by the retarded propagator of the field, which plays an essential role in the factorization identity we prove for the field Kraus operators.
DOI: 10.1103/sxkx-sy9g
Authors: Robin Simmons, Maria Papageorgiou, Marios Christodoulou, Časlav Brukner
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W4416780383