ALP Seminar: Towards experimental falsifications of some nonlocal, superdeterministic and retrocausal explanations of quantum mechanics

Joint work with Carlos Vieira and Ravishankar Ramanathan.

The experimental violation of Bell inequalities implies that at least one of the assumptions in Bell's theorem fails in nature. Existing experiments are inconclusive about which are the assumptions that fail. As a consequence, possible explanations of Bell non-locality include theories with different amounts of instantaneous "actions at a distance", different degrees of "measurement dependence" (that may occur due to limitations to freedom of choice or to retrocausal influences), and combinations thereof. Here, we drastically narrow down the possibilities. We first show that any non-local hidden-variable (HV) theory with outcome independence (OI) and arbitrary joint relaxation of measurement independence (MI) and parameter independence (PI) can be experimentally excluded in a Bell-like experiment on specific high-dimensional entangled states. Then, we show that any non-local HV theory with MI, PI and arbitrary relaxation of OI can also be experimentally excluded using specific qubit-qubit entangled states. These results demonstrate that Bell's theorem is just the tip of an iceberg: quantum theory does not only offer advantage in information processing, communication and computation with respect to "local" models, but also with respect to any model that allows partial instantaneous actions at a distance or that only partially constrain freedom of choice or only allow for partial retrocausal influences.