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quant-ph2026
Causality from the spectrum: Emergence of causal order from process-matrix mereology
Varun Kushwaha, Nicolas Loizeau, Alexei Grinbaum +1
In Hamiltonian systems, the only basis-independent quantity is the spectrum. Given a spectrum, quantum mereology seeks preferred tensor-product decompositions into local subsystems…
quant-ph2026
Frame perspectives for process matrices: from coordinate parametrization to spacetime representation
Luca Apadula, Alexei Grinbaum, Äaslav Brukner
We study how to implement and transform frame perspectives for quantum processes in the process-matrix formalism. We argue that, for pure processes, the causal reference frames (CR…
quant-ph2025
Agency under indefinite causality: operational eternalism in higher-order quantum theory
Alexei Grinbaum
After two decades of research on indefinite causality, a conceptual lesson emerges: the tension between operational quantum theory and dynamical spacetime physics requires observer…