Title:

Alternative theories in quantum foundations

Abstraction is an important driving force in theoretical physics. New insights often accompany the creation of physical frameworks which are both comprehensive and parsimonious. In particular, the analysis of alternative sets of theories which exhibit similar structural features as quantum theory has yielded important new results and physical understanding. An important task is to undertake a thorough analysis and classiﬁcation of quantumlike theories. In this thesis, we take a step in this direction, moving towards a synthetic description of alternative theories in quantum foundations. After a brief philosophical introduction, we give a presentation of the mathematical concepts underpinning the foundations of physics, followed by an introduction to the foundations of quantum mechanics. The core of the thesis consists of three results chapters based on the articles in the author’s publications page. Chapter 4 analyses the logic of stabilizer quantum mechanics and provides a complete set of circuit equations for this subtheory of quantum mechanics. Chapter 5 describes how quantumlike theories can be classiﬁed in a periodic table of theories. A pictorial calculus for alternative physical theories, called the ZX calculus for qudits, is then introduced and used as a tool to depict particular examples of quantumlike theories, including qudit stabilizer quantum mechanics and the SpekkensSchreiber toy theory. Chapter 6 presents an alternative set of quantumlike theories, called quantum collapse models. A novel quantum collapse model, where the rate of collapse depends on the Quantum Integrated Information of a physical system, is introduced and discussed in some detail. We then conclude with a brief summary of the main results.
