  Entanglement lies at the heart of quantum mechanics and in recent years has
been identified as an essential resource for quantum information processing and
computation. Creating highly entangled multi-particle states is therefore one
of the most challenging goals of modern experimental quantum mechanics,
touching fundamental questions as well as practical applications. Here we
report on the experimental realization of controlled collisions between
individual neighbouring neutral atoms trapped in the periodic potential of an
optical lattice. These controlled interactions act as an array of quantum gates
between neighbouring atoms in the lattice and their massively parallel
operation allows the creation of highly entangled states in a single
operational step, independent of the size of the system. In the experiment, we
observe a coherent entangling-disentangling evolution in the many-body system
depending on the phase shift acquired during the collision between neighbouring
atoms. This dynamics is indicative of highly entangled many-body states that
present novel opportunities for theory and experiment.
