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Master thesis: Investigation of Spin Qubits in Semiconductor/Superconductor hybrid systems

Jan 23rd, 2020

Due to their low effective electron mass, high electron mobility and high Rashba spin-orbit coupling InAs nanowires are considered to hold great potential for realizing spin-qubit systems and therefore are an appealing candidate for applications such as Quantum computation. However, in order to build any real quantum computer system, single qubits need to be coupled over larger distances. So far, only coupling between directly neighbouring quantum-dot qubits have been realized by adjusting electrostatic barriers. Recently, coupling mechanisms employing superconductivity have been proposed. This is expected to provide coupling over distances larger than the coherence length of the superconductor. Experimentally this is realized by in-situ covering InAs nanowires with a superconducting shell such as Al or Nb. To achieve proper and well-defined coupling strengths a precisely controlled interface between semiconductor and superconductor is essential. Tuning of the interaction will be realized by creating ultrathin potential barriers at the interface. Fabrication of the required well-defined interfaces in a fully in-situ process is enabled by the Nanocluster at FZ Jülich.

This project aims at the realization of electrostatically defined spin qubits in InAs nanowires and investigation of the coupling provided by the superconducting shell. The effect of various dielectric barriers and thicknesses as well as superconducting materials on the coupling strength will be examined. Characterisation of spin qubit performance and coupling interaction will be performed by electrical measurements at cryogenic temperatures of a few mK. For this purpose, a variety of cryostats enabling electrical measurements at different magnetic fields and base temperatures is available in the group’s laboratory.

Nanowire Josephson junction with backgateNanowire Josephson junction with backgate
Copyright: Patrick Zellekens

Prof. Dr. Thomas Schäpers
Peter Grünberg Institut PGI-9, Building 02.11, Room 105
Tel.Nr.: +49 (0)2461 61 2668