Novel entangling gates and scalable trap designs for trapped-ion quantum computing
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Date
2024-12-19
Authors
Quinn, Alexander
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Publisher
University of Oregon
Abstract
Trapped ions have received much attention as a platform for quantum computing, a purpose they may be well-suited for on account of their natural features: Ions of the same species are inherently identical; they can be manipulated using electric and magnetic fields via both their net charge, which allows external fields to couple to ions’ center-of-mass motion, and via internal electronic transitions; and when they are isolated from the environment, their states can remain coherent for long time spans, at least by the standards of quantum information experiments. Despite these features, the ability to carry out useful quantum computing in trapped ions is limited, with two major practical constraints being 1) the difficulty of coherently controlling ions’ states and 2) the limited physical scale of existing trapped-ion quantum computers, which typically hold no more than tens of ions. This document present a set of projects meant to help address these limitations through different tracks, including the development and testing of control techniques for trapped ions and the design of new types of traps. Firstly, we present an entangling gate carried out on quantum bits (qubits) encoded in a set of electronic energy levels that have been relatively unexplored until recently and whose viability for quantum information processing may enable more efficient architectures for trapped ion quantum computing. Specifically, we entangled a pair of qubits encoded in two Zeeman sublevels of the D5/2 metastable excited state of a pair of trapped 40Ca+ ions using Raman laser beams 10s of THz detuned from resonance to limit scattering rates (a fundamental error source in Raman gates). We demonstrate that high-fidelity gates (98.6(1)% subtracting state preparation and measurement error, and 99.1(1)% subtracting both SPAM and erasure) can be performed with this encoding scheme, show that the main source of error is technical noise, and employ a leakage detection scheme that allows decay or deshelving from the metastable level to be heralded, potentially making correcting this class of errors easier. After this, we shift focus from control techniques and discuss scalable trap design, focusing on a project to fabricate ion traps using 3D printing, a technique that could potentially enable microfabricated traps with high harmonicity, power efficiency, and depth of confinement relative to the 2D (planar) microfabricated traps widely used in efforts to scale up trapped-ion quantum computing. We design, simulate, fabricate, and carry out preliminary electrical testing on metallized trap prints, demonstrating some minimum viability of the technique, and show computationally that traps produced this way could have trapping characteristics similar to those of other 3D microfabricated designs. Finally, we consider scalable trap design for continuousvariable quantum computing (CVQC), a quantum computing scheme where, in trapped ions, information is encoded in the states of the vibrational modes of an ion crystal. A key requirement for universal CVQC is the ability to perform non-Gaussian operations, which can be difficult to carry out electronically. In this work, we present a 2D ion trap design that can perform non-Gaussian motional operations in an all-electronic way, with the design process accounting for the geometric limitations imposed by 2D traps. We consider some of the motional operations possible with this trap and estimate their associated coupling rates, finding that under a reasonable set of assumptions about operating parameters, coupling rates for non-Gaussian operations could be achieved that are comparable to those previously achieved with all-electronic Gaussian operations could likely be achieved with this trap design. This dissertation includes co-authored, published material.
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Keywords
3d printing, continuous-variable quantum computing, ions, paul traps, quantum computing, trapped ions