Entanglement of mesoscopic systems

The entanglement of clouds of atoms recently experimentally verified is expressed in terms of the fluctuation algebra introduced by Goderis, Verbeure and Vets. A mean field Hamiltonian describing the coupling to a laser beam leads to different time evolutions if considered on microscopic or mesoscopic operators. Only the latter creates non trivial correlations that finally after a measurement lead to entanglement between the clouds.