Non-local quantum correlations and detection processes in QFT

TL;DR

This paper investigates quantum detection in quantum field theory, revealing that standard approximations like RWA introduce non-local effects, while alternative models maintain locality in detector responses.

Contribution

It provides an exact analysis of detector responses in a simple QFT model, highlighting the impact of common approximations on locality and correlation detection.

Findings

RWA causes non-local detector responses

Non-standard models preserve locality in detection

Vacuum contributions relate to zero-point field correlations

Abstract

Quantum detection processes in QFT must play a key role in the description of quantum field correlations, such as the appearance of entanglement, and of causal effects. We consider the detection in the case of a simple QFT model with a suitable interaction to exact treatment, consisting of a quantum scalar field coupled linearly to a classical scalar source. We then evaluate the response function to the field quanta of two-level point-like quantum model detectors, and analyze the effects of the approximation adopted in standard detection theory. We show that the use of the RWA, that characterizes the Glauber detection model, leads in the detector response to non-local terms corresponding to an instantaneously spreading of source effects over the whole space. Other detector models, obtained with non-standard or the no-application of RWA, give instead local responses to field quanta, apart from source independent vacuum contribution linked to preexisting correlations of zero-point field.