A reconstruction of finite-dimensional quantum theory where all of the postulates are stated entirely in diagrammatic terms, making them intuitive, and necessary additional axioms for a process theory to correspond to the Hilbert space model are characterised.Expand

Surprisingly, it is shown that the quadratic lower bound holds regardless of the order of interference, which means that post-quantum interference does not imply a computational speed-up over quantum theory.Expand

It is argued that if one can identify axioms for a realist causal-inferential theory such that the notions of causation and inference can differ from their conventional (classical) interpretations, then one has the means of defining an intrinsically quantum notion of realism, and thereby a realists representation of operational quantum theory that salvages the spirit of locality and of noncontextuality.Expand

The advent of quantum computing has challenged classical conceptions of which problems are efficiently solvable in our physical world. This motivates the general study of how physical principles… Expand

This work asks whether there exists an operationally defined theory superseding quantum theory, but which reduces to it via a decoherence-like mechanism and proves that no such post-quantum theory exists if it is demanded that it satisfy two natural physical principles: causality and purification.Expand

Recently, table-top experiments involving massive quantum systems have been proposed to test the interface of quantum theory and gravity. In particular, the crucial point of the debate is whether it… Expand

It is shown that any theory with a classical limit must contain entangled states, thus establishing entanglement as an inevitable feature of any theory superseding classical theory.Expand

It is shown that defining a notion of purity for processes in general process theories has to make reference to the leaks of that theory, a feature missing in standard definitions; hence, a refined definition is proposed and the resulting notion ofurity for quantum, classical and intermediate theories is studied.Expand

It is shown that if a classical computer requires at least n queries to solve a learning problem, then the corresponding “no-information” lower bound in theories lying at the kth level of Sorkin’s hierarchy is n, which leaves open the possibility that quantum oracles are less powerful than general probabilistic oracles.Expand

It is argued that simplex-embeddability constitutes an intuitive and freestanding notion of classicality for GPTs, which has applications to witnessing nonclassicality in prepare-measure experiments.Expand