TLDR
Scientists have shown that pairs of helium atoms can be linked in such a way that changing one instantly affects the other, even when they are far apart. This proves a strange prediction of quantum physics using moving atoms, not just light.
Summary
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1 Study Aim
The main goal of this paper is to demonstrate Bell correlations—evidence of quantum entanglement and nonlocality—in the motion (momentum states) of pairs of ultracold helium atoms. The authors aim to show that measurements on one atom can instantly influence its entangled partner, even when separated, using their movement rather than internal properties like spin or polarization. Simply put: The study wants to prove that moving atoms can be linked in a way that changing one instantly changes the other, just like in famous quantum experiments with light.
2 Study Design
The researchers created a Bose-Einstein condensate (BEC) of helium atoms and used laser pulses to split and collide the atoms, generating pairs of atoms with opposite momenta (momentum-entangled pairs). They manipulated these pairs using a matter-wave Rarity-Tapster interferometer, which mixes and measures the momentum states of the atoms. The experiment used precise detection equipment to track individual atoms and measure correlations between their momenta. Data was collected from thousands of experimental runs, focusing on events where only one pair was detected in the relevant momentum states, to closely match the ideal conditions for testing Bell's inequality. Simply put: The team made very cold helium atoms collide, watched how pairs of them moved, and checked if their movements were mysteriously linked.
3 Findings
The study reveals strong correlations between the momenta of entangled helium atom pairs, with measurements showing oscillations that match quantum predictions for a Bell state. The observed correlation amplitude was high enough (A = 0.86) to violate a steering inequality, ruling out a large class of local hidden variable theories. This provides direct evidence of quantum nonlocality in the motion of massive particles, not just in light or internal atomic states. The authors suggest that with further improvements, their setup could test even stricter forms of Bell's inequality and explore the effects of gravity on quantum states. The results open new possibilities for quantum information technologies and fundamental tests of physics. Simply put: The experiment showed that the movements of atom pairs are linked in a way that can't be explained by ordinary physics, confirming a weird prediction of quantum theory.