Lecture Notes on Quantum Electrical Circuits

During the last 30 years, stimulated by the quest to build superconducting quantum processors, a theory of quantum electrical circuits has emerged, which is called circuit quantum electrodynamics or circuit-QED. The goal of the theory is to provide a quantum description of the most relevant degrees of freedom. The central objects to be derived...

In-situ bandaged Josephson junctions for superconducting quantum processors

Shadow evaporation is commonly used to micro-fabricate the key element of superconducting qubits—the Josephson junction. However, in conventional two-angle deposition circuit topology, unwanted stray Josephson junctions are created which contribute to dielectric loss. So far, this could be avoided by shorting the stray junctions with a so...

QuCAT: Quantum circuit analyzer tool in Python

Quantum circuits constructed from Josephson junctions and superconducting electronics are key to many quantum computing and quantum optics applications. Designing these circuits involves calculating the Hamiltonian describing their quantum behavior. Here we present QuCAT, or 'Quantum Circuit Analyzer Tool', an open-source framework to help in...

Hard Superconducting Gap and Diffusion-Induced Superconductors in Ge-Si Nanowires

We show a hard superconducting gap in a Ge-Si nanowire Josephson transistor up to in-plane magnetic fields of 250 mT, an important step toward creating and detecting Majorana zero modes in this system. A hard gap requires a highly homogeneous tunneling heterointerface between the superconducting contacts and the semiconducting nanowire. This...

Spin-Orbit Interaction and Induced Superconductivity in a One-Dimensional Hole Gas

Low dimensional semiconducting structures with strong spin-orbit interaction (SOI) and induced superconductivity attracted great interest in the search for topological superconductors. Both the strong SOI and hard superconducting gap are directly related to the topological protection of the predicted Majorana bound states. Here we explore the...

Side Gate Tunable Josephson Junctions at the LaAlO₃/SrTiO₃ Interface

Novel physical phenomena arising at the interface of complex oxide heterostructures offer exciting opportunities for the development of future electronic devices. Using the prototypical LaAlO₃/SrTiO₃ interface as a model system, we employ a single-step lithographic process to realize gate-tunable Josephson junctions...

Quantum transport in superconducting hybrids: Molecular devices and layered materials

In this thesis we investigate superconducting hybrids made from two material systems, namely, molecules and layered materials. For studies of superconducting phenomena in molecular junctions we develop two platforms which rely on the superconducting proximity effect to preserve pre-existing nano-gap formation techniques and bonding chemistries....

Thickness dependent interlayer transport in vertical MoS₂ Josephson junctions

Wereport on observations of thickness dependent Josephson coupling and multiple Andreev reflections (MAR) in vertically stacked molybdenum disulfide (MoS₂)-molybdenum rhenium (MoRe) Josephson junctions. MoRe, a chemically inert superconductor, allows for oxide free fabrication of high transparency vertical MoS₂ devices....

Suspended carbon nanotubes coupled to superconducting circuits

Carbon nanotubes are unique candidates to study quantum mechanical properties of a nanomechanical resonator. However to access this quantum regime, present detectors are not yet sensitive enough. In this thesis we couple a carbon nanotube CNT mechanical resonator to a superconducting circuit which is a root towards such sensitivity.

Asymmetric current-phase relation due to spin-orbit interaction in semiconductor nanowire Josephson junction

We theoretically study the current-phase relation in semiconductor nanowire Josephson junction in the presence of spin-orbit interaction. In the nanowire, the impurity scattering with strong SO interaction is taken into account using the random matrix theory. In the absence of magnetic field, the Josephson current I and phase difference ?...

Effects and detection of quantum noise

This thesis is about random fluctuations over time (or noise) of electric currents and voltages occuring in small (mesoscopic) electronic devices with typical sizes of micro- to nanometre. Even though the theory presented is of a more general nature, research into such systems has been greatly pushed forward by the prospect of building a quantum...