Loaded array of magnetic microtraps. A two-dimensional absorption image of the atomic distribution (shown in false-colour) after transfer to the magnetic lattice. Atoms populate more than 500 array sites over a region of 1.4x 0.4 mm². The optical resolution is approximately 4 µm. The scale bar corresponds to a distance of 200 µm. Abstract
We have recently produced the first two-dimensional lattice of magnetic microtraps for ultracold atoms based on patterned magnetic films . We combine the robust nature of neutral atoms with respect to environmental decoherence and integrated-circuit-like technology to create a new platform for quantum information science. This novel system bridges the gap between individual atomic clouds manipulated with chip-scale microtraps and optical lattices which contain a single atom per site.
We load hundreds of tightly confining and optically resolved array sites with mesoscopic atom clouds, each containing 10-1000 atoms (see figure), and subsequently cool them to the temperature required for quantum degeneracy. We have shuttled the atoms across the surface using the atom chip as an atomic shift register, the cold-atom analog of an electronic CCD. Local manipulation is achieved using focused lasers.
High atomic densities have allowed a small and well defined number of atoms to be prepared in each trap. We use absorption imaging and advanced image processing techniques to reliably detect as few as 1 to 10 atoms per lattice site and apply spatial correlation analysis to the measured density distributions to reveal the quantum fluctuations typical of mesoscopic atomic systems.
Currently we are studying site-resolved hyperfine state coherence on the chip and investigating laser excited Rydberg states of the atoms to mediate long-range interactions between neighbouring microtraps. Rydberg excitations may be used to entangle mesoscopic ensembles of atoms for use in quantum information processing . We expect this system to be the ideal platform for studying many particle entanglement and quantum information processing with neutral atoms on a chip.
 S. Whitlock, R. Gerritsma, T. Fernholz and R. J. C. Spreeuw, New J. Phys. 11, 023021 (2009).
 M. Muller, I. Lesanovsky, H. Weimer, H. P. Buchler, and P. Zoller, accepted Phys. Rev. Lett. (2009).