The process of taming and engineering the quantum world has been highly successful for single quantum objects, or simple pair systems. Outstanding results have recently been obtained with ion traps, including the demonstration of quantum gates and quantum teleportation. However, the great promise of quantum coherent manipulation lies in systems composed of several or even many subsystems. Thus the scalability of the physical systems is now becoming a central issue.

The systems of interest have to satisfy two partly conflicting conditions: Firstly, in order to achieve scalability they must be distributed, i.e., composed of many subsystems, which can be manipulated independently, usually by virtue of spatial separation. Secondly, quantum coherence has to be maintained for the whole system. No system is currently available that fully meets both requirements. In the framework of the Research Unit, we study systems of cold neutral atoms which are one of the most promising candidates to approach this exciting goal in a coordinated effort of 5 research groups in Bonn, Hannover, and Garching.

Experimental work will be carried out with a medium scale 1D lattice of atoms which can individually be controlled, with a large scale 2D and 3D lattice where massive entanglement has already been demonstrated, and with correlated atom-photon states to connect subsystems of the neutral atom ensembles. Theoretical work will be focused on the development of measures for large scale entanglement as well as the realizations of simple quantum simulators closely following the original proposals by Richard P. Feynman. The joint experimental and theoretical efforts in this network offer an ideal basis for testing concepts of large scale entanglement and gaining insight into the question how growing complexity affects quantum correlations of the multi-particle system.