Efficient discrimination between real and complex quantum theories

Abstract

We improve the test to show the impossibility of a quantum theory based on real numbers by a larger ratio of complex-to-real bound on a Bell-type parameter. In contrast to previous theoretical and experimental proposals the test requires three setting for the parties $A$ and $C$, but also six settings for the middle party $B$, assuming separability of the sources. The bound for this symmetric configuration imposed on a real theory is $14.88$ whilst the complex maximum is $18$. This large theoretical difference enables us to demonstrate the concomitant experimental violation on IBM quantum computer via a designed quantum network, obtaining as a result $15.44$ at more than $80$ standard deviations above the real bound.