Entangling many atomic ensembles through laser manipulation

We propose an experimentally feasible scheme to generate the Greenberger-Horne-Zeilinger-type of maximal entanglement between many atomic ensembles based on laser manipulation and single-photon detection. The scheme, with inherent fault tolerance to the dominant noise and efficient scaling of the efficiency with the number of ensembles, allows one to maximally entangle many atomic ensembles within the reach of current technology. Such a maximum entanglement of many ensembles has wide applications in the demonstration of quantum nonlocality, high-precision spectroscopy, and quantum information processing.