Spinful Andreev States in Superconducting Circuits

The growing understanding of the physics of superconductor-semiconductor nanostruc- tures is a key driver for the development of emerging quantum technologies. The elemen- tary excitations of these hybrid nanostructures are Andreev bound states. To further our knowledge about their intricate physics, new tools must be used to study them. This...

Josephson Effects in Frequency-Domain Multiplexed TES Microcalorimeters and Bolometers

Frequency-division multiplexing is the baseline read-out system for large arrays of superconducting transition-edge sensors (TES’s) under development for the X-ray and infrared instruments like X-IFU (Athena) and SAFARI, respectively. In this multiplexing scheme, the sensors are ac-biased at different frequencies from 1 to 5 MHz and operate...

Josephson effects in carbon nanotube mechanical resonators and graphene

Magnetic interference pattern in planar SNS Josephson junctions

Epitaxial aluminum nitride tunnel barriers grown by nitridation with a plasma source

High critical current-density (10?to?420?kA/cm2) superconductor-insulator-superconductor tunnel junctions with aluminum nitride barriers have been realized using a remote nitrogen plasma from an inductively coupled plasma source operated in a pressure range of 10?3–10?1?mbar. We find a much better reproducibility and control compared to previous...

Low-frequency noise in Josephson junctions for superconducting qubits

The authors have studied low-frequency resistance fluctuations in shadow-evaporated Al/AlOx/Al tunnel junctions. Between 300 and 5?K the spectral density follows a 1/f law. Below 5?K, individual defects distort the 1/f shape of the spectrum. The spectral density decreases linearly with temperature between 150 and 1?K and saturates below 0.8?K....

Single-charge transport in coupled nanostructures

This thesis research is focussed on the development of strongly coupled single-charge devices. Single-charge devices are sub-micrometer sized electronic circuits that use the fact that charge is quantized. Their main component is the tunnel junction, a resistive element that can be made as small as one nanometer. In the past, many different...

Quantum Superpositions of Persistent Josephson Currents

This thesis presents experimental research on Josephson junction devices that behave quantum mechanically. The devices are formed by micrometer-sized superconducting islands, that are interconnected by a Josephson tunnel junction: a thin insulating layer between two superconductors. With current microfabrication technology it is possible to make...