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

Abstract

The ability to control and tune interactions in ultracold atomic gases has paved the way for the realization of new phases of matter. So far, experiments have achieved a high degree of control over short-range interactions, but the realization of long-range interactions has become a central focus of research because it would open up a new realm of many-body physics. Rydberg atoms are highly suited to this goal because the van der Waals forces between them are many orders of magnitude larger than those between ground-state atoms. Consequently, mere laser excitation of ultracold gases can cause strongly correlated many-body states to emerge directly when atoms are transferred to Rydberg states. A key example is a quantum crystal composed of coherent superpositions of different, spatially ordered configurations of collective excitations. Here we use high-resolution, in situ Rydberg atom imaging to measure directly strong correlations in a laser-excited, two-dimensional atomic Mott insulator. The observations 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. Together with a time-resolved analysis, this supports the description of the system in terms of a correlated quantum state of collective excitations delocalized throughout the gas. Our experiment demonstrates the potential of Rydberg gases to realize exotic phases of matter, thereby laying the basis for quantum simulations of quantum magnets with long-range interactions.

Chirped pulse excitation of two-atom Rydberg states

“…The second approach has not yet been realized experimentally and is currently a subject of active theoretical investigation [7][8][9]. Interactions in Rydberg states can also find applications in quantum simulation [10,11], quantum repeaters [12], and in the realization of efficient and non-local nonlinearities [13], down to a single photon level [14].…”

Dipoles on a two-leg ladder

“…Measuring the bulk ordering such as Ising and string orders seems very realistic given current experimental developments using singlesite addressing 78,79 . In particular, string order in Mott insulators have been probed in one dimension 80 and crystal structure has been probed in a Rydberg gas in two dimensions 81 . Even dynamics has been accessible in recent experiments 82 .…”

Ionization of Rydberg atoms by standing-wave light fields

“…An essential experimental tool in our work has been an optical lattice, which enables spatially resolved photoionization. The storage and manipulation of Rydberg atoms in laser traps is important in several emerging areas, including the realization of exotic phases of matter 20 , field sensors 21 , quantum information processing [22][23][24] and highprecision measurements of fundamental constants 25 . In these applications, photoionization can either represent a mechanism through which Rydberg atoms are lost, or be exploited as a detection method 26,27 .…”