Thorvald Wadum Larsen

A thesis for the degree of Doctor of Philosophy defended November 2018.

The PhD School of Science, Faculty of Science,  Center for Quantum Devices, Niels Bohr Institute, University of Copenhagen

Supervisor:
Charles M. Marcus

Mesoscopic Superconductivity towards Protected Qubits

Several unsolvable problems, such as molecular simulations of drugs, are predicted to be computable with a quantum computer. However, current state-of-the-art quantum bits, qubits, are error-prone making large computations impossible. This thesis presents results from experimental studies of three different approaches towards error-protected qubits based on novel semiconductor nanowires proximitized by an epitaxially grown aluminium shell.

First, we develop gatemons, a semiconductor-based superconducting qubit, as a viable qubit for quantum error correction. Next, we introduce a novel circuit architecture based on the high-transmission of semiconductor Josephson junction to create a protected 0-pi qubit. Finally, we demonstrate a high field compatible superconducting qubit for detection of Majorana states which are predicted to form protected qubits.