Institute of Nuclear Physics Polish Academy of Sciences, Poland, ewa.borsuk@ifj.edu.pl
(joint work with P. Błasiak)
Quantum three box paradox is a prototypical example of some bizarre predictions for intermediate measurements made on pre- and post-selected systems. Although in principle those effects can be explained by measurement disturbance, it is not clear what mechanisms are required to fully account for the observed correlations. In this talk, three box paradox is scrutinised from a causal point of view. We consider an array of potential causal structures behind the experiment, eliminating those without enough explanatory power. This gives us a way of differentiating between the various mechanisms in which measurement disturbance can propagate in the system. Specifically, we distinguish whether it is just the measurement outcome or the full measurement context that is required for the causal explanation of the observed statistics. We show that the latter is indispensable, but only when the full statistics is taken into account (with any of the three boxes being checked in the experiment). We also discuss a distinction between the pure and realist causal setting, where the latter assumes that measurements reveal preexisting values. While in the pure case the original version of the paradox can be explained without resorting to any measurement disturbance, this fails when the full statistics is taken into account. The realist case is more stringent in this respect. These various results illustrate the richness of the paradox which is better appreciated from the causal perspective.