Investigations and implementations of superconducting quantum architectures

This thesis presents a series of experimental investigations into superconducting artificial atoms. The central element of the devices is the Josephson junction, and its dual counterpart the quantum phase slip junction that operates by the coherent tunnelling of flux quanta. Circuits embedding these elements are designed, simulated and tested at cryogenic temperatures to explore fundamental quantum phenomena, new materials and new devices more robust against decoherence.

The main text is divided into four sections covering: the generation of single photons using a transmon qubit with the main work developing the fabrication and measurement protocols for a time-resolved readout of the source's correlation functions; the investigation into a new type of dipole qubit that promises to improve flux noise sensitivity through the symmetric modification of a standard flux qubit's geometry - a proposal of a Hamiltonian that can match experiment data is given, and a detailed analysis on the potential energy landscape and transition amplitudes is performed; the coherent quantum phase slip qubit realised in TiN opens the window to the fabrication of compact quantum circuits using nanowires, while the demonstration of its readout through a capacitively coupled resonator offers design and material flexibility in the future studies of these dual devices; the twin coherent phase slip qubit is an interesting attempt at creating a distributed network supporting flux quanta, which is assigned an initial model that attempts to describe its rich experimental spectrum.

Supplementing the main text is a sizeable, self-contained appendix tasked with reminding the reader of the relevant superconducting and quantum theory, collected from a variety of literature, as well as walk through the more involved proofs and fabrication steps used in the realisation of all of the devices.

This thesis will be of most use for researchers working hands on with superconducting qubits in the lab, looking to capture the essential quantum optics theory required for the design and measurement of novel quantum structures.