Entanglement from the vacuum

We explore the entanglement of the vacuum of a relativistic field by letting a pair of causally disconnected probes interact with the field. We find that, even when the probes are initially non-entangled, they can wind up to a final entangled state. This shows that entanglement persists between disconnected regions in the vacuum. However the probe entanglement, unlike correlations, vanishes once the regions become sufficiently separated. The relation between entropy, correlations and entanglement is discussed.Comment: 15 pages, 2 figures, Latex2e, see also quant-ph/0008006. To appear in a special issue of Foundations of Physics in honor of Jacob Bekenstei