This shows ytterbium ions in an ion Coulomb crystal, taken with an EMCCD camera (electron multiplying CCD camera). The ionized atoms fluoresce in the laser light; the distance between the ions is approx. 10 µm to 20 µm.
In the upper rows, different symmetrical ion arrangements (phases) are encountered in the central area of the Coulomb crystal: (a) linear, like a string of pearls (symmetrical to the rotational axis); (b) two-dimensional in zigzag (Z2 symmetry), and (c) as a three-dimensional helix. If, however, a fast transition from one phase to another is induced with force, irregularities occur: (d) localized defect between two areas which are actually symmetrical, and (e) extended defect in which the ions slowly change from one zigzag orientation to its mirror symmetry.