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

TL;DR

This paper investigates causality violations in relativistic quantum detector models, highlighting how non-relativistic assumptions can lead to superluminal signaling and challenging the validity of certain quantum field measurements.

Contribution

It reveals the connection between non-relativistic detector models and superluminal signaling, questioning the validity of some measurement protocols in quantum field theory.

Findings

Non-relativistic detector models predict superluminal propagation.

Causal factorization can be violated in extended non-relativistic models.

Implications for the validity of quantum field 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.