Integration of Trapped Ion System and Sympathetic Cooling with Multi-isotope Ions

Abstract

This dissertation addresses challenges in quantum computing with trapped ions, including system integration of the trapped ion hardware, heating-induced decoherence, and efficient cooling mechanisms, by investigating multi-species or isotope ion chains with sympathetic cooling techniques. The study explores loading ion chains with 174Yb and 138Ba species, using an Nd:YAG ablation laser for isotope-selective trapping. A detail of the design of a compact room-temperature trapped ion system is presented, comprising an ultra-high vacuum (UHV) package, a micro-fabricated surface trap, and a small form-factor ion pump, demonstrating trapping of 174Yb+ ions and achieving a suitable vacuum level. A detailed ion chain cooling model based on sympathetic cooling addresses the heating problem of 171Yb+ qubits on a two-dimensional surface trap, revealing the crucial role of the mass ratio between cooling and qubit ions in the sympathetic cooling dynamics. The dissertation further delves into the implementation of sympathetic cooling in trapped ion systems, successfully cooling qubit 171Yb+ ions using 172Yb+ or 174Yb+ ions as cooling ions, reducing motional heating and decoherence without direct interaction with qubits. In summary, this dissertation contributes to developing and optimizing compact trapped ion systems for quantum computing, providing insights on multi-species ion chains, sympathetic cooling techniques, and ion chain cooling models to enhance trapped ion quantum computing performance and fidelity.