Hybrid Josephson junction-based quantum devices in magnetic field

The technology of quantum computing is believed to solve certain computational problems significantly faster than classical computers, enabling classically inaccessible problems. However, the technology is still in its infancy and it is still too early to conclude which physical system(s) will form the basis of tomorrow's quantum computer. Small...

Advances in semiconducting-superconducting nanowire devices

After a century from the quantum description of nature, the scientific community has laid the basis for using nature's properties to our advantage. The quantum technology vision stems from the idea of capitalizing these principles in various sectors, such as computation and communication. However, in contrast to classical processors, encoding...

Single-Shot Fabrication of Semiconducting–Superconducting Nanowire Devices

Semiconducting–superconducting hybrids are vital components for the realization of high-performance nanoscale devices. In particular, semiconducting–superconducting nanowires attract widespread interest owing to the possible presence of non-abelian Majorana zero modes, which are quasiparticles that hold promise for topological quantum...

InSbAs Two-Dimensional Electron Gases as a Platform for Topological Superconductivity

Topological superconductivity can be engineered in semiconductors with strong spin-orbit interaction coupled to a superconductor. Experimental advances in this field have often been triggered by the development of new hybrid material systems. Among these, two-dimensional electron gases (2DEGs) are of particular interest due to their inherent...

Josephson junctions in superconducting coplanar DC bias cavities: Fundamental studies and applications

This thesis investigates fundamental properties of Josephson junctions embedded in microwave circuits, and an application arising from this hybrid approach. We used the versatility of superconducting coplanar DC bias cavities to extract previously inaccessible information on phase coherent and subgap mechanisms of graphene Josephson junctions....

Energy structure of hybrid Semiconductor-superconductor nanowire Based devices

Materials possessing superconducting properties are highly sought after due to their potential technological applications. Much of the work has focused on utilising a thin insulating barrier separating a pair of superconducting electrodes, a Josephson junction, as a workhorse in the field of superconducting based quantumcomputation. Yet such...

Coherence and nonlinearity in mechanical and josephson superconducting devices

In this thesis, the microwave detection of mechanically compliant objects is investigated. This starts with a system of a suspended metal drum capacitively coupled to a high impedance microstrip resonator. The mechanical non-linear dissipation of the drums is studied. Next, a suspended nanowire coupled to a CPW resonator is studied. With an...

Electronic Transport in Helium Beam Modified Graphene and Ballistic Josephson Junctions

This thesis describes the capabilities of the helium ion microscope (HIM) and that of graphene to explore fundamental physics and novel applications. While graphene offers superior electronic properties, the helium ion microscope allows us to combine imaging and modification of materials at the nanoscale. We used the capabilities of HIM to grow...

Semiconductor Nanowire Josephson Junctions: In the search for the Majorana

Due to the collective behavior of electrons, exotic states can appear in condensed matter systems. In this PhD thesis, we investigate semiconducting nanowire Josephson junctions that potentially have Majorana zero modes (MZM) as exotic states. MZM are expected to form a robust quantum bit and quantum operations are done by interchange, otherwise...

Current-Phase Relation of Ballistic Graphene Josephson Junctions

The current-phase relation (CPR) of a Josephson junction (JJ) determines how the supercurrent evolves with the superconducting phase difference across the junction. Knowledge of the CPR is essential in order to understand the response of a JJ to various external parameters. Despite the rising interest in ultraclean encapsulated graphene JJs,...

Improved Nb SIS devices for heterodyne mixers between 700?GHz and 1.3?THz with NbTiN transmission lines using a normal metal energy relaxation layer

In this paper, we demonstrate experimentally the implementation of a niobium-trilayer junction with an aluminum-oxide tunnel barrier, embedded in a high-gap superconducting niobium-titanium-nitride circuit. Previously reported heating by quasiparticle trapping is removed by inserting a normal metal layer of gold between the niobium junction and...

Superconducting Quantum Interference based Electromechanical Systems

Mechanical sensors are essential tools for the detection of small forces. This thesis presents the dc SQUID as a detector for the displacement of embedded micromechanical resonators. The device geometry and basic operating principle are described. The SQUID displacement detector reaches an excellent resolution, a factor of 1.5 below the standard...

Superconducting flux qubits: Quantum chains and tunable qubits

This thesis presents results of theoretical and experimental work on superconducting persistent-current flux quantum bits. These qubits are promising candidates for the implementation of scalable quantum information processing. This work focuses on the study of one dimensional chains of inductively coupled flux qubits and on qubits with a...

Superconducting Quantum Circuits

This thesis describes a number of experiments with superconducting cir- cuits containing small Josephson junctions. The circuits are made out of aluminum islands which are interconnected with a very thin insulating alu- minum oxide layer. The connections form a Josephson junction. The current trough the junction is related to the superconducting...

Single electron and Cooper pair tunneling in circuits of small tunnel junctions