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Causality is central to understanding the mechanisms of nature: some event "A" is the cause of another event "B". Surprisingly, causality does not follow this simple rule in quantum physics: due to to quantum superposition we might be led to believe that "A causes B" and that "B causes A". This idea is not only important to the foundations of physics but also leads to practical advantages: a quantum circuit with such indefinite causality performs computationally better than one with definite causality. This thesis provides one of the first comprehensive introductions to quantum causality, and presents a number of advances. It provides an extension and generalization of a framework that enables us to study causality within quantum mechanics, thereby setting the stage for the rest of the work. This comprises: mathematical tools to define causality in terms of probabilities; computational tools to prove indefinite causality in an experiment; means to experimentally test particular causal structures; and finally an algorithm that detects the exact causal structure in an quantum experiment.
List of contents
Introduction.- Causal and causally separable processes.- Witnessing causal nonseparability: theory and experiment.- Causal polytopes.- Experimental test of a classical causal model for quantum correlations.- A quantum causal discovery algorithm.- Conclusions.
About the author
Dr Giarmatzi obtained her Physics degree from Aristotle University of Thessaloniki, in Greece. After a short visit to rainy Paris for her Masters, and cloudy Brussels for an attempt at a PhD, she settled in sunny Brisbane, at The University of Queensland, for her PhD. Right after the thesis submission she remained at UQ, as a PostDoctoral Research Fellow until present. Having explored different theoretical aspects of quantum causality, now her interests lay in exploiting them to aid quantum technologies.
