Jørn Kløvfjell Mjelva

This dissertation comprises three self-standing papers investigating the metaphysics of quantum entanglement and its explanatory role in accounting for the non-classical correlations exhibited by entangled systems. It defends entanglement realism, the view that entanglement reflects a genuine metaphysical feature of systems in entangled states. While this position aligns with a scientific realist attitude towards entanglement, it has been argued to be undermined by entanglement swapping, particularly in delayed-choice and spacelike scenarios. This objection is addressed in the first two papers. The first (Ch. 2) analyses delayed-choice entanglement swapping in both a collapsebased and a no-collapse framework, arguing that a realist account remains viable. It also considers spacelike entanglement swapping, concluding that it only presents a problem for a collapse account. This problem is addressed in the second paper (Ch. 3), which develops a realist-friendly relativistic collapse account of entanglement swapping. The third paper (Ch. 4) addresses metaphysical concerns, specifically that entanglement realism challenges key elements of our intuitive worldview by implying some form of “holistic unity”. It proposes a novel approach to the link view on entanglement – a view which explicates entanglement in terms of physical relations rather than holistic unity – that addresses the main objections raised against the link view by developing it in a formalism based on the Heisenberg picture of quantum mechanics. Taken together, the dissertation advances a positive case for entanglement realism as a straightforwardly scientific realist view that accounts for quantum correlations – even in the entanglement swapping case – which can also be made compatible with key elements of our intuitive worldview.

Delayed-choice entanglement swapping experiments have been argued to undermine realism about entanglement. One response has been to argue that the correlations displayed in delayed-choice entanglement swapping experiments have a different physical interpretation than the correlations in the non-delayed case. This strategy runs into problems when applied to cases of spacelike entanglement swapping, as it would appear to require one to either posit a privileged foliation of spacetime or otherwise accept that whether entanglement obtains is frame dependent. In this article, I present a realist-friendly account of entanglement swapping that circumvents this dilemma, in which entanglement is explicated via the notion of a common ground. The issue of frame dependence is resolved by adopting the past light-cone criterion for property attribution, and the correlations displayed in the spacelike entanglement swapping experiments are attributed to a joint common ground.

In recent years, there has been a growing interest in the possibility of temporal nonlocality, mirroring the spatial nonlocality supposedly evidenced by the Bell correlations. In this context, Glick (2019) has argued that timelike entanglement and temporal nonlocality is demonstrated in delayed-choice entanglement swapping (DCES) experiments, like that of Ma et al. (2012), Megidish et al. (2013) and Hensen et al. (2015). I will argue that a careful analysis of these experiments shows that they in fact display nothing more than “ordinary” spacelike entanglement, and that any purported timelike entanglement is an artefact of selection bias. Regardless any other reason one may have for challenging the assumption of temporal locality, timelike entanglement as evidenced by these experiments is not among them. I conclude by discussing what lessons on the nature of entanglement might be drawn from an examination of DCES experiments.