  In 1935, Einstein, Podolsky and Rosen (EPR) conceived a Gedankenexperiment
which became a cornerstone of quantum technology and still challenges our
understanding of reality and locality today. While the experiment has been
realized with small quantum systems, a demonstration of the EPR paradox with
spatially separated, massive many-particle systems has so far remained elusive.
We observe the EPR paradox in an experiment with two spatially separated
Bose-Einstein condensates containing about 700 Rubidium atoms each. EPR
entanglement in conjunction with individual manipulation of the two condensates
on the quantum level, as demonstrated here, constitutes an important resource
for quantum metrology and information processing with many-particle systems.
Our results show that the conflict between quantum mechanics and local realism
does not disappear as the system size is increased to over a thousand massive
particles.
