Spectra and ground states of one- and two-dimensional laser-driven   lattices of ultracold Rydberg atoms
  We investigate static properties of laser-driven, ultracold Rydberg atoms confined to one- and two-dimensional uniform lattices in the limit of vanishing laser coupling. The spectral structure of square lattices is compared to those of linear chains and similarities as well as differences are pointed out. Furthermore, we employ a method based on elements of graph theory to numerically determine the laser detuning-dependent ground states of various lattice geometries. Ground states for chains as well as square and rectangular lattices are provided and discussed. 
Wolfgang Zeller, Michael Mayle, Thorsten Bonato, Gerhard Reinelt,   Peter Schmelcher
physics.atom-ph quant-ph