Open quantum systems and applications to the quantum information theory

• Κύριος συγγραφέας: Kolioni, Theodora
• Άλλοι συγγραφείς: Αναστόπουλος, Χαράλαμπος
• Μορφή: Thesis
• Γλώσσα: English
• Έκδοση: 2020
• Θέματα: Open quantum system; Quantum brownian motion model; Markovian dynamics; Perturbation theory; Master equation; Entanglement; Einstein causality; Locality; Fermi problem; Non-Markovian dynamics; Quantum information; Dissipation kernel; Noise kernel; Correlation functions; Entanglement harvesting; Ανοικτά κβαντικά συστήματα; Μοντέλο κβαντικής κίνησης Μπράουν; Μαρκοβιανή δυναμική; Θεωρία διαταραχών; Εξίσωση Μάστερ; Εναγκαλισμός; Αιτιότητα; Τοπικότητα; Πρόβλημα Φέρμι; Μη-Μαρκοβιανή δυναμική; Κβαντική πληροφορία; Μήτρα διασποράς; Μήτρα θορύβου; Συναρτήσεις συσχέτισης; Εξαγωγή εναγκαλισμού από το κενό

This thesis is a contribution to the debate on (a) fully understanding and describing the communication between remote systems through quantum fields, and (b) constructing a theoretical model for accurately describing the information transmission, which does not lead to a violation of causality. To this end, we studied the system of two localized detectors (oscillators) interacting through a mass-less scalar quantum field in a vacuum state via an Unruh-DeWitt coupling. This system admits an exact solution is providing a good model for addressing fundamental issues in particle-field interactions, causality, and locality in quantum field measurements that are relevant to proposed quantum experiments in space. Our analysis of the exact solution led to the following results. (i) Common approximations used in the study of analogous open quantum systems fail when the distance between the detectors becomes of the order of the relaxation time. In particular, the creation of correlations between remote detectors is not well described by ordinary perturbation theory and the Markov approximation. (ii) There is a unique asymptotic state that is correlated; it is not entangled unless the detector separation is of the order of magnitude of the wavelength of the exchanged quanta. (iii) The evolution of seemingly localized observables is non-causal. The latter is a manifestation of Fermi’s two-atom problem, albeit in an exactly solvable system. We argue that the problem of causality requires a re-examination of the notion of entanglement in relativistic systems, in particular, the physical relevance of its extraction from the quantum vacuum.