a) 30 ytterbium ions are trapped in a linear radio-frequency trap. Laser 1 irradiates the whole crystal and makes it fluoresce. This light is collected by means of a high-resolution lens and imaged onto a camera. Laser 2 is aligned to one of the chains, so that a differential light force acts between them. b) Schematic representation of the model system: The ions interact with each other and with the trap via springs. Due to a structural defect, spacings a1 and a2 are mismatched.