We use laser-cooled ion Coulomb crystals in the well-controlled environment of a harmonic radiofrequency ion trap to investigate phase transitions and defect formation. Topological defects in ion Coulomb crystals (kinks) have been recently proposed for studies of nonlinear physics with solitons and as carriers of quantum information. Defects form when a symmetry breaking phase transition is crossed nonadiabatically. For a second order phase transition, the Kibble–Zurek mechanism predicts that the formation of these defects follows a power law scaling in the rate of the transition. We demonstrate a scaling of defect density and describe kink dynamics and stability. We further discuss the implementation of mass defects and electric fields as first steps toward controlled kink preparation and manipulation.

We present a new setup to sympathetically cool 115In+ ions with 172Yb+ for optical clock spectroscopy. A first prototype ion trap made of glass-reinforced thermoset laminates was built, based on a design that minimizes axial micromotion and offers full control of the ion dynamics in all three dimensions. We detail the trap manufacturing process and the characterization of micromotion in this trap. A calibration of the photon-correlation spectroscopy technique demonstrates a resolution of 1.1 nm in motional amplitude of our measurements. With this method, we demonstrate a sensitivity to systematic clock shifts due to excess micromotion of \(|(\Updelta\nu/\nu)_{\rm mm}|=7.7\times10^{-20}\) along the direction of the spectroscopy laser beam. Owing to our on-board filter electronics on the ion trap chips, no rf phase shifts could be resolved at this level. We measured rf fields over a range of 400 μm along the ion trap axis and demonstrated a region of 70 μm where an optical frequency standard with a fractional inaccuracy of ≤1 × 10−18 due to micromotion can be operated.

We study experimentally and theoretically the properties of structural defects (kink solitons) in two-dimensional ion Coulomb crystals. We show how different types of kink solitons with different physical properties can be realized, and transformed from one type into another by varying the aspect ratio of the trap confinement. Further, we discuss how impurities in ion Coulomb crystals, such as mass defects, can modify the dynamics of kink creation and their stability. For both pure and impure crystals, the experimentally observed kink dynamics are analyzed in detail and explained theoretically by numerical simulations and calculations of the Peierls-Nabarro potential. Finally, we show that static electric fields provide a handle to vary the influence of mass defects on kinks in a controlled way and allow for deterministic manipulation and creation of kinks.

Femtosecond laser structuring is applied to produce linear ion traps of AlN ceramics. Such ion trap can serve as an optical clock with exceptionally high long term stability. The selection of techniques, applicable to the high precision microstructuring of AlN ceramics, is limited due to high hardness and fragility of the material. Laser structuring is very attractive for this application. However, long laser pulses cause thermal decomposition and surface metallization of AlN ceramics. A femtosecond laser allows material removal without adverse heat effects. At the same time high quality surface finish together with aspect ratios and precision as required for optical ion trap clocks are ensured. Here, a high process throughput of up to 400 μm3/pulse and a sub-pristine surface roughness down to 350 nm Ra were achieved. The novelty of this structuring technique lies in the separation of processing stages and the application of two distinctive femtosecond laser induced phenomena: ablation and plasma etching. Rapid material removal for the rough contouring is achieved by material ablation with a focused laser beam. The remaining rough surface is further refined to the required specifications by plasma polishing. The laser beam then acts indirectly and serves as a source of energy to sustain a plasma plume in the near vicinity of the substrate.

We present the status of our new experiment to lasercool linear chains of 172Yb+ and 115In+ ions for an optical clock based on the 1S0-3P0 transition in 115In+. We successfully have trapped and laser-cooled Coulomb crystals of 172Yb+ ions in our new scalable ion trap that are used to characterize the trap and to sympathetically cool 115In+ ions. We could demonstrate an area of more than 65 μm, where the fractional frequency shifts due to time dilation are below 10-18 for both ions.