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TY  - THES
AU  - Zellekens, Patrick
TI  - Towards semiconductor-superconductor hybrid quantum circuits : Gatemon and Andreev qubits based on InAs/Al, InAs/Nb and GaAs/InSb core/shell nanowires
PB  - RWTH Aachen University
VL  - Dissertation
CY  - Aachen
M1  - RWTH-2023-07601
SP  - 1 Online-Ressource : Illustrationen, Diagramme
PY  - 2022
N1  - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2023
N1  - Dissertation, RWTH Aachen University, 2022
AB  - In this thesis, two different qubit concepts and their respective pre-stages are investigated. The Gatemon is a variant of the famous and well-studied Transmon. Both have in common that they rely onthe macroscopic and collective excitation of an anharmonic LC circuit and are a very promising approach to realize scalable qubit systems. The Andreev qubit, on the other hand, is based on a singlepair of Andreev bound states and the two-particle transitions associated with it. Both mentioned systems have in common that they can be realized by means of semiconductor nanowires. Thus, the major part of this thesis is devoted to the characterization and subsequent optimization of nanowire-based devices treated with (high frequency) electromagnetic fields at ultralow and ambient temperatures. Using InAs/super-conductor core/shell nanowires that have been in-situ and epitaxially covered with a thin metal layer out of Al, Nb or other materials, mesoscopic Josephson junctions are fabricated and subsequently investigated by means of advanced experimental DC and AC techniques. On the low frequency and DC side, we utilize emission, SQUID, magnetoconductance and quantum dot measurements to characterize the electronic properties of the fabricated devices including the hardness of the induced proximity gap, the interface transparency, the carrier concentration and the phase coherence length. In addition, we search for signatures of 4π-periodic supercurrent contributions. Here, a special focus is set on InAs/Al full shell nanowires that, following theoretical predictions, can host pairs of Majorana fermions and, in combination with the Little-Parks effect, do not require a complicated braiding procedure to manipulate the state of the system. The last part of the thesis is focused on flux- and gate-dependent measurements of Andreev qubits as well as the investigation of individual Andreev bound states by means of two-tone spectroscopy. The latter one reveals an unconventional state structure that is connected to the occurrence of single quasiparticle transitions caused by a Rashba-induced lifting of the spin degeneracy. This is one of the prerequisites for the realization of a helical gap and topologically-protected states. In addition, a nanowire-based 2D Gatemon was successfully realized. The analysis of the detuning-dependent Rabi oscillations exhibit a gate-tunable resonator-qubit coupling and reasonable large lifetimes of the two-level system T1 ≈ 120ns.
LB  - PUB:(DE-HGF)11
DO  - DOI:10.18154/RWTH-2023-07601
UR  - https://publications.rwth-aachen.de/record/962752
ER  -