Spectroscopy of Trapped ¹³⁸Ba⁺ Ions for Atomic Parity Violation and Optical Clocks

Abstract

The Standard Model of particle physics describes the behavior of all known elementary particles. This theory is remarkably successful in explaining the dynamics of the subatomic world (see also the recent discovery of the predicted Higgs boson). Nevertheless, it leaves various fundamental questions unanswered. How can the theory of general relativity, which describes gravity, be unified with the Standard Model, which leaves out this force? Or what constitutes the dark matter that is hypothesized to explain astrophysical observations? These and other questions motivate exploring the limits of the Standard Model. In the search for new physics, several approaches exist. The Large Hadron Collider near Geneva, which discovered the Higgs boson, has the brute force to directly create new particles. However, working at a smaller scale and lower energy is also possible. The goal of the research presented in this thesis is to test the Standard Model using precision measurements and atomic physics techniques. This research focusses on using a single barium (Ba⁺) or radium ion (Ra⁺) that is slowed down using laser cooling and trapped in vacuum by an oscillating electric field. This enables high precision measurements to test the Standard Model description of the weak interaction in atoms (atomic parity violation) and test whether the fundamental constants are truly constant (optical atomic clocks). In preparation of these experiments, this thesis describes several spectroscopic measurements on trapped ¹³⁸Ba⁺ ions, including transition frequencies and lifetimes of atomic levels. This information is crucial for the atomic structure calculation necessary for interpreting future measurement results.