Phys.org  May 2, 2022 An international team of researchers (France, Germany, Spain) has discovered a new connection between superposition and entanglement that does not assume that quantum theory is correct. They proved that given any two general probabilistic theories (GPTs) the following are equivalent: (i) each theory is nonclassical, (ii) each theory satisfies a strong notion of incompatibility equivalent to the existence of “superpositions” and (iii) the two theories can be entangled, in the sense that their composite exhibits either entangled states or entangled measurements. Intuitively, in the post-quantum GPT setting, a superposition is a set of two binary ensembles […]