Control and Readout of High-Dimensional Trapped Ion Qudits

Abstract

The trapped ion platform is one of the quantum computing platforms that is at the forefront for realizing large-scale quantum information processing, which is crucial for practically actualizing the advantages of quantum algorithms. Scaling up the trapped ion quantum computing architecture remains a challenge. We explore an alternative avenue in a trapped ion system for increasing the computational Hilbert space other than trapping more ions, which is by increasing the qudit dimension of an ion. Our ion of choice is ¹³⁷Ba⁺, which has a rich energy level structure for high-dimensional qudit encoding. Utilizing the additional energy states found in ¹³⁷Ba⁺ also comes with non-trivial complexities that require careful considerations, which we have solved and report in this thesis. We report on a single-shot state measurement protocol which allows qudit encoding in ¹³⁷Ba⁺ of up to 25 levels, and demonstrate state preparation and measurement of up to 13 levels, which is unprecedented in a trapped ion system.

This thesis is written with hopes that it is complete enough as a guide for readers who wants to work with trapped barium ions. The bring up and calibration methods of equipment parameters are reported in this thesis, along with detailed studies of some experimental observations that may not be intuitively clear. Ion loading via laser ablation is also explored in this work, which is a less commonly used ion loading method. To more effectively load the less abundant ¹³⁷Ba⁺ isotope from a natural abundance source, we employed the resonance enhanced multiphoton ionization process and report on the improved isotope selectivity. Although not directly related to trapped ion quantum information processing, a cost-effective beam pointing stabilization solution that we have developed is presented, which we hope to be helpful to any laboratories with free-space laser beams.