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.