Magnetically-induced topological phases in superconductor-semiconductor qubits

Superconducting circuits are one of the leading approaches to realising a quantum computer. Our recent work has established that semiconductors can be used to manipulate superconducting qubits and improve the prospects for scaling beyond a few hundred [1]. Furthermore, the superconductor can induce special phases of electronic matter in the semiconductor that can be used to create a revolutionary type of qubit that is less affected by disturbances in the environment [2]. In many of these schemes the electrons need to be in strong global magnetic fields that weaken the superconducting properties and performance of the qubit. One way around this is to use local ferromagnetic films and dopants in or nearby the semiconductor [3]. The aim of this PhD project is to realise such zero-field topological qubits. Specifically, we will use the helical field from nanomagnet arrays to induce topological phases in proximitised III-V nanostructures and demonstrate Josephson coupling across magnetically-doped V-VI semiconductors. We will then integrate these Josephson elements into a superconducting qubit and use circuit quantum electrodynamics to show enhanced relaxation and dephasing times relative to conventional non-topological qubits.