A key resource for distributed quantum-enhanced protocols is entanglement between spatially separated modes. Yet, the robust generation and detection of nonlocal entanglement between spatially separated regions of an ultracold atomic system remains a challenge. Here, we use spin mixing in a tightly confined Bose-Einstein condensate to generate an entangled state of indistinguishable particles in a single spatial mode. We show experimentally that this local entanglement can be spatially distributed by self-similar expansion of the atomic cloud. Spatially resolved spin read-out is used to reveal a particularly strong form of quantum correlations known as Einstein-Podolsky-Rosen steering between distinct parts of the expanded cloud. Based on the strength of Einstein-Podolsky-Rosen steering we construct a witness, which testifies up to genuine five-partite entanglement.
@article{arxiv.1708.02407,
title = {Spatially distributed multipartite entanglement enables Einstein-Podolsky-Rosen steering of atomic clouds},
author = {Philipp Kunkel and Maximilian Prüfer and Helmut Strobel and Daniel Linnemann and Anika Frölian and Thomas Gasenzer and Martin Gärttner and Markus K. Oberthaler},
journal= {arXiv preprint arXiv:1708.02407},
year = {2018}
}