Relativistic causality in particle detector models: Faster-than-light signalling and "Impossible measurements"

Abstract

We analyze potential violations of causality in Unruh DeWitt-type detector models in relativistic quantum information. We proceed by first studying the relation between faster-than-light signaling and the causal factorization of the dynamics for multiple detector-field interactions. We show in what way spatially extended non-relativistic detector models predict superluminal propagation of the field's initial conditions. We draw parallels between this characteristic of detector models, stemming from their non-relativistic dynamics, and Sorkin's "impossible measurements on quantum fields" arXiv:gr-qc/9302018. Based on these features, we discuss the validity of measurements in QFT when performed with non-relativistic particle detectors.