Observation of spatially ordered structures in a two-dimensional Rydberg gas

The ability to control interactions in ultra-cold atomic gases has paved the way for the realization of new phases of matter with short-range interactions. Rydberg atoms, which are strongly interacting via van der Waals forces, are promising candidates to gain the same amount of control over long-range interacting systems. Here we report on the experimental observation of strong correlations between laser-excited Rydberg atoms using a high-resolution optical detection scheme. The measurements reveal the emergence of spatially ordered excitation patterns with random orientation, but well-defined geometry in the high-density components of the prepared many-body state. The developed techniques might allow for the deterministic adiabatic preparation of ordered states and the investigation of their coherence properties. In combination with single-site addressing the Rydberg atom imaging techniques will enable experiments towards quantum information processing. \\[4pt] [1] P. Schau{\ss} et al., Nature 491, 87 (2012)