Abstract
Bell correlations are a foundational demonstration of how quantum entanglement contradicts the classical notion of local realism. Rigorous validation of quantum nonlocality have only been achieved between solid-state electron spins, internal states of trapped atoms, and photon polarisations, all weakly coupling to gravity. Bell tests with freely propagating massive particles, which could provide insights into the link between gravity and quantum mechanics, have proven to be much more challenging to realise. Here we use a collision between two Bose-Einstein condensates to generate spin entangled pairs of ultracold helium atoms, and measure their spin correlations along uniformly rotated bases. We show that correlations in the pairs agree with the theoretical prediction of a Bell triplet state, and observe a quantum mechanical witness of Bell correlations with 6sigma significance. Extensions to this scheme could find promising applications in quantum metrology, as well as for investigating the interplay between quantum mechanics and gravity.
Highlights
Bell correlations are a foundational demonstration of how quantum entanglement contradicts the classical notion of local realism
Any description of the system will be incompatible with local realism[1,2], which requires the particles to be in a defined state at all times and not to communicate faster than the speed of light
This work shows that a collision of Bose–Einstein condensate (BEC) generates pairwise entanglement
Summary
Bell correlations are a foundational demonstration of how quantum entanglement contradicts the classical notion of local realism. We show that correlations in the pairs agree with the theoretical prediction of a Bell triplet state, and observe a quantum mechanical witness of Bell correlations with 6σ significance. Extensions to this scheme could find promising applications in quantum metrology, as well as for investigating the interplay between quantum mechanics and gravity. 1234567890():,; The basic scheme of a Bell test, originally proposed by John Bell[1], involves measuring correlated detector events between a pair of spin-12 particles arriving at spatially separated detectors A and singlet state jΨÀi 1⁄4 ðj"iA.
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