2016/02/08 by M. Ringbauer, C. Giarmatzi, R. Chaves +3
Physics and Astronomy · #quant-ph
paper · pdf · doi:10.1126/sciadv.1600162
published as Science Advances, Vol. 2, no. 8, e1600162 (2016)
arxiv created 2016/02/08 · arxiv updated 2016/09/05
Explaining observations in terms of causes and effects is central to all of empirical science. Correlations between entangled quantum particles, however, seem to defy such an explanation. To recover a causal picture in this case, some of the fundamental assumptions of causal explanations have to give way. Here we consider a broad class of models where one of these assumptions, Bell's local causality, is relaxed by allowing a direct influence from one measurement outcome to the other. We use interventional and observational data from a photonic experiment to bound the strength of this causal influence in a two-party Bell scenario and test a novel Bell-type inequality for the considered models. Our results demonstrate the incompatibility of quantum mechanics with an important class of nonlocal causal models, which includes Bell's original model as a special case. Recovering a classical causal picture of quantum correlations thus requires an even more counter-intuitive modification of our classical notion of cause and effect.