Exploring Quantum Foundations with Single Photons

Abstract

Quantum mechanics is our most successful physical theory and has been confirmed to extreme accuracy, yet, a century after its inception it is still unclear what it says about the nature of reality. In this thesis, I explore some of the foundational questions which are central to our understanding of quantum mechanics using single photons as an experimental platform. Three experiments form the core of the thesis, studying, respectively, the role of reality, causality, and uncertainty in quantum mechanics. These experiments shed light on decade-old questions that have previously been thought to be outside the realm of experimental physics. The results contribute to our understanding of the structure of quantum mechanics, and reveal novel aspects of phenomena that were believed to be well understood. In three further experiments I also touch upon the topics of finding physical principles behind quantum mechanics, quantum effects in extreme gravitational fields, and developing a pathway towards tests of macroscopic quantum phenomena. Starting out as a fringe discipline, the field of quantum foundations has developed into an influential area of research. It is now becoming possible to turn many of the foundational questions in quantum mechanics from topics of philosophy into topics of physics. Subjecting these questions to rigorous experimental tests the field is making progress in the quest for understanding our best physical theory.i Declaration by authorThis thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis.I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award.I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School.I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis.ii Publications during candidaturePeer-re...

First-Principles Investigation of Spin–Phonon Coupling in Vanadium-Based Molecular Spin Quantum Bits

“…The procedure outlined in the Computational Methods section has been employed for the 1-4 crystal structures, whose details are summarized in Table I and Figure S5 in the SI. The coordination geometries around the metal centres are square pyramidal, for the penta-coordinate compounds (1,3), and trigonally-distorted octahedral for the hexa-coordinate ones (2,4). It is worth noting that the metal-ligand (V-L) distances in sulphur-containing ligands are longer than those of the oxygen ones (Table I), consistent with the difference in atomic radius between O and S.…”

The End of a Classical Ontology for Quantum Mechanics?

“…The ontological models framework was first introduced in [ 15 ], and developed further in [ 16 ] (see also [ 17 , 18 ] for good reviews), and provides a formalisation of our notion of classical ontology in an operational model of quantum processes [ 1 ]. As an operational model, the framework specifies a set of possible preparations, transformations, and measurements, and associated outcome probabilities, to describe the observed statistics over the possible outcomes.…”

“…As we saw above, by denying this assumption and accounting for the correlation between hidden variables, or the ontic state , and the measurement procedure by way of causal symmetry, we can rescue the assumption that any beables are local. As a result of this move, then, we can see that the admission of causal symmetry is a ready made violation of the assumption of a strict temporal and causal order for the ontological models framework [ 18 ] (p. 94).…”

An Introduction to Operational Quantum Dynamics

“…(see, e.g. [77,99] for a more in-depth introduction to quantum tomography). Then (8) captures precisely the idea of quantum process tomography [26,76], where the dynamics of a quantum system is experimentally reconstructed by relating a basis of input states to their corresponding outputs.…”