A matter-wave Rarity–Tapster interferometer to demonstrate non-locality

We present an experimentally viable approach to demonstrate quantum non-locality in a matter-wave system via a Rarity–Tapster interferometer using two s-wave scattering halos generated by colliding helium Bose–Einstein condensates. The theoretical basis for this method is discussed, and its suitability is experimentally quantified. As a proof of concept, we demonstrate an interferometric visibility of V= 0.42 (9) , corresponding to a maximum CSHS-Bell parameter of S= 1.1 (1) , for the Clauser–Horne–Shimony–Holt (CHSH) version of the Bell inequality, between atoms separated by ∼ 4 correlation lengths. This constitutes a significant step toward a demonstration of a Bell inequality violation for motional degrees of freedom of massive particles and possible measurements of quantum effects in a gravitationally sensitive system.