Hi all,
Tomorrow Lukas Schmitt will tell us about his Masterthesis with Vilasini entitled 'Operational causality and realizable processes in the Page-Wootters framework'. See below for the abstract. The talk will take place at 15:45 in HIT E 41.1.
Best, Ladina
Title: Operational causality and realizable processes in the Page-Wootters framework
Abstract:
Causality is a fundamental concept in science, but its definition varies across different disciplines. In quantum information theory, causality is associated with the flow of information, while in relativity, it is linked to spacetime geometry. Inspired by quantum gravity, the process matrix framework was proposed to describe indefinite causal structures in the information theoretic sense. However, the physical interpretation and realizability of general process matrices remain open questions. To address such questions, this work explores the set of process matrices realizable in the Page-Wootters (PW) framework by formulating operational notions of causality there. The PW framework is commonly used in quantum gravity models and describes quantum dynamics relative to a clock which is itself a quantum system. We investigate how operational causality notions such as signaling can be formalized in terms of PW history states and whether relativistic causality violations such as backwards in time signaling are possible in the PW framework. Our main contributions include defining signaling in PW states, developing a visual representation of PW states, finding constraint operators of PW states of causally indefinite processes, and characterizing the class of realizable processes in the PW framework under monotonically increasing clocks. Furthermore, we explore the consequences of backward ticking clocks and investigate their signaling structure. Non-causal processes such as the Lugano process can be realized in such a setting, but backward ticking clocks lead to normalization issues that challenge a physical interpretation.