This thesis describes experimental work towards the development of a trapped-ion quantum
computer based on microchip ion traps and long-wavelength radiation, using magnetic
field gradients. The relationship between experimental parameters and two-qubit
gate fidelity is investigated for microchips with two different static magnetic field gradient
generation methods. For current-carrying wires and under-chip permanent magnets,
optimum ion heights of 110 μm and 200 μm are found respectively.
Construction of an experiment capable of demonstrating high-fidelity gates is reported,
including innovations for the use of microchip ion traps with permanent magnets. The development
of a vacuum system for versatile microchip experiments is described, including
new methods for impedance-matched RF delivery, in-vacuum filtering and liquid nitrogen
microchip cooling. Protection of both the microchip surface from atomic flux and of ions
from the charged imaging viewport are both investigated in detail.
A new preparation framework for microchip ion traps before their use in experiments
is developed. In order to remove unwanted deposited layers on the microchips, a process
of multiple chemical treatments is used. In addition, these characterisation efforts lead to
refinement of the microfabrication process for future microchips.
The application of large currents to microchips is of fundamental importance to scalable
trapped-ion quantum computing using static magnetic field gradients. As part of the
characterisation process, currents of ≈ 10A are successfully applied to microfabricated
current-carrying wires, demonstrating the viability of these structures for generation of
local magnetic fields and gradients in a quantum computing device.
The operation of a microchip ion trap experiment with under-chip permanent magnets
for a high magnetic field gradient (≈ 140Tm−1) is described. The successful trapping
of ytterbium-174 and -171 ions is reported, as well as their use to measure and optimise
the ion trap parameters. The thesis concludes with consideration of the expected future
results from the ongoing operation of the experiment.