Quantum Correlations Are Stronger Than All Nonsignaling Correlations Produced by n -Outcome Measurements
We show that, for any n , there are m -outcome quantum correlations, with m >n , which are stronger than any nonsignaling correlation produced from selecting among n -outcome measurements. As a consequence, for any n , there are m -outcome quantum measurements that cannot be constructed by selecting locally from the set of n -outcome measurements. This is a property of the set of measurements in quantum theory that is not mandatory for general probabilistic theories. We also show that this prediction can be tested through high-precision Bell-type experiments and identify past experiments providing evidence that some of these strong correlations exist in nature. Finally, we provide a modified version of quantum theory restricted to having at most n -outcome quantum measurements.