PhD Thesis Defence | Maria Papageorgiou, Local measurements in Relativistic Quantum Information: localisation and signalling

Zoom (please email amgrad@uwaterloo.ca for the meeting link)

Candidate 

Maria Papageorgiou | Applied Mathematics, University of Waterloo

Title

Local measurements in Relativistic Quantum Information: localisation and signalling

 Abstract

In this thesis, we study some foundational aspects of detector models in quantum field theory (QFT) related to signalling and localisation, and we analyze certain frictions with relativistic causality. We are characterizing the spatiotemporal information that can be extracted from the field using various detector models in different regimes and we define a signaling estimator, based on quantum metrology, that can be used to quantify how much signalling can be transmitted reliably through the quantum field. We analyze ‘impossible measurements’ scenarios in which the microcausality condition in QFT is not sufficient for blocking superluminal signalling between detectors coupled to the field.

Further, we are interpreting the detector’s response in different regimes, for single-particle wavepacket states or coherent states of the field. There are well-known results that indicate that QFT does not admit a particle ontology, so we ask the question: what do detectors detect? In the weak coupling regime, we recover particle-like phenomenology, related to the phenomenon of resonance and ‘time-of-arrival’. In the strong coupling regime, we demonstrate how a continuous pointer variable gets correlated with smeared field time-averages. We also consider solvable models (QBM) that can be used to characterize the weak, strong and intermediate regimes. We demonstrate how field measurements, resonance and time-of-arrival phenomena arise in the QBM model. Finally, we point towards some counter-intuitive aspects of the localized detection of massive wavepackets.