We study experimentally and theoretically structural defects which are formed during the transition from a laser cooled cloud to a Coulomb crystal, consisting of tens of ions in a linear radio frequency trap. We demonstrate the creation of predicted topological defects ("kinks") in purely two-dimensional crystals and also find kinks which show novel dynamical features in a regime of parameters not considered before. The kinks are always observed at the center of the trap, showing a large nonlinear localized excitation, and the probability of their occurrence saturates at ∼0.5. Simulations reveal a strong anharmonicity of the kink's internal mode of vibration, due to the kink's extension into three dimensions. As a consequence, the periodic Peierls-Nabarro potential experienced by a discrete kink becomes a globally confining potential, capable of trapping one cooled defect at the center of the crystal.

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Trapping and laser cooling in atomic physics enables control of single particles and their dynamics at the quantum level in a background-free environment. Ultrashort intense laser pulses reveal the ultimate control of electromagnetic fields, enabling the imaging of matter, in principle down to a single molecule or virus resolved on atomic scales. However, current methods fall short in overlapping each target with a pulse of comparable size. We combine the two fields by demonstrating a deterministic molecular conveyor, formed of electric trapping potentials. We deliver individual diatomic ions at millikelvin temperatures and with submicrometre positioning into few-femtosecond ultraviolet laser pulses. We initiate and probe the molecule’s femtosecond dynamics and detect it and its response with 100% efficiency. This experiment might become key for investigations of individual molecules, such as structural determinations using few-femtosecond X-ray lasers. Our scheme may overlap each single molecule with a pulse, focused to (sub)micrometre size, providing the required number of photons at the repetition rate of the laser