Davydas Razmadze

Exploring Superconducting Phases in Hybrid Nanowire Devices

The thesis explores the superconducting properties of hybrid InAs/Al nanowire devices where trivial and topological regimes can be studied using high/low-frequency measurement techniques.

The first chapter introduces the theoretical background of superconductivity to understand the phenomena in the experimental data. We continue by presenting semiconducting nanowire quantum devices that were studied in this thesis. Detailed fabrication recipes for full/half-shell Al nanowire devices are introduced together with experimental setups for transport measurements.

The thesis continues by demonstrating improved tunability of overlapping gate geometries compared to conventional side-gated devices, allowing clean and effective characterization of hybrid nanowire junctions. The following chapters present full-shell Al/InAs nanowires interferometer devices, where novel means of probing topological states in the nanowires are possible by changing the parity of the quantum-dot in the Josephson junctions. Further, the display of subgap-state splitting that decays with finite length in Majorana islands is presented, suggesting the topological nature of full-shell nanowires.

The thesis concludes with radio-frequency and dispersive readout methods that are compatible with nanowire-based quantum devices. This enables fast device tuning and characterization. The measured signal-to-noise ratios of these sensors suggest that these techniques could be used for future topological nanowire qubit measurements.

Via Zoom: https://ucph-ku.zoom.us/j/62676708579