Laser Spectroscopy on Os- : A Prerequisite for the Laser Cooling of Atomic Anions

Laser cooling of neutral atoms or positive ions is today routinely employed in numerous experiments. Negative ions, in contrast, have distinct characteristics which hamper the application of lasers for cooling. But in 1999, the discovery of the unique bound–bound electric dipole transition in the negative osmium ion provided the motivation for a first cooling attempt. This thesis presents the first milestones toward the ultimate goal of laser cooling negative osmium, including high-resolution laser spectroscopy of the relevant bound–bound E1 transition. Its frequency – between the ground 4F9/2 and the 6DJe1 (bound) excited states – was determined to be 257.831190(35) THz in 192Os-, in agreement with a previous measurement, but two orders of magnitude more precise. The determination of the resonant cross-section implicitly provided the corresponding Einstein A coefficient, which was found to be A ~ 330 s-1. Furthermore, the isotope shift of the E1 transition and the hyperfine structure constants of the ground and excited state were obtained, for the first time, from the analysis of the spectra of all naturally abundant isotopes. The hyperfine structure revealed the heretofore unknown total angular momentum of the excited state to be Je1 = 9/2. Finally, laser spectroscopy in an external magnetic field confirmed the expected line splitting for Os- due to the Zeeman effect. Based on all these experimental results the prospect of laser cooling negative osmium is reviewed

Time-resolved observation of thermalization in an isolated quantum system

We use trapped atomic ions forming a hybrid Coulomb crystal and exploit its phonons to study an isolated quantum system composed of a single spin coupled to an engineered bosonic environment. We increase the complexity of the system by adding ions and controlling coherent couplings and, thereby, we observe the emergence of thermalization: Time averages of spin observables approach microcanonical averages while related fluctuations decay. Our platform features precise control of system size, coupling strength, and isolation from the external world to explore the dynamics of equilibration and thermalization

Arrays of individually controlled ions suitable for two-dimensional quantum simulations

A precisely controlled quantum system may reveal a fundamental understanding of another, less accessible system of interest. A universal quantum computer is currently out of reach, but an analogue quantum simulator that makes relevant observables, interactions and states of a quantum model accessible could permit insight into complex dynamics. Several platforms have been suggested and proof-of-principle experiments have been conducted. Here, we operate two-dimensional arrays of three trapped ions in individually controlled harmonic wells forming equilateral triangles with side lengths 40 and 80 μm. In our approach, which is scalable to arbitrary two-dimensional lattices, we demonstrate individual control of the electronic and motional degrees of freedom, preparation of a fiducial initial state with ion motion close to the ground state, as well as a tuning of couplings between ions within experimental sequences. Our work paves the way towards a quantum simulator of two-dimensional systems designed at will