Science http://doi.org/bs3b (2016)

Science http://doi.org/bs3c (2016)

Trapping single atoms at low temperatures using optical potentials has become routine. However, creating ordered, defect-free arrays of cold atoms is another story. It's possible to create a regular array of optical tweezers serving as placeholders for the atoms, but achieving 100% filling of the prepared sites is difficult. The nature of the loading process is non-deterministic, which leads to unfilled sites — that is, defects.

But Daniel Barredo and colleagues have found a way to get defect-free 2D cold-atom arrays. Starting from a half-filled array of rubidium atoms, they imaged the occupancies with a CCD camera, then moved the atoms around by repositioning the tweezers. They calculated the sequence of atomic displacements needed to convert the initial random structure into a defect-free array with a pre-defined structure.

Meanwhile, Manuel Endres and co-workers worked out how to create defect-free linear chains of cold rubidium atoms. They too started with a stochastic loading of their array and then visualized the occupancies. Atoms were moved, along a fixed direction, to fill up vacancies. Different orderings were realized, including equally-spaced chains of only a few atoms.