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Disputation Jacob Fridolin Steiner

09.05.2023 | 14:30
Thema der Dissertation:
Quantum Engineering with Subgap and Boundary Modes Topology, Correlation and Information in Designer Quantum Systems
Abstract: In recent decades, quantum engineering has emerged as a subfield of condensed matter physics with the objective of designing materials and devices without classical counterparts. In this context, we focus on the use of subgap and boundary modes of superconductors and topological materials for the quantum engineering of novel phases, devices, and response characteristics. This thesis encompasses several subtopics, all falling under this umbrella. First, we discuss the competition between quantum magnetism and topological superconductivity in a chain of Yu-Shiba-Rusinov subgap states. We establish that quantum spin impurities on a superconductor are described by an effective t-J model with a drastically reduced phase space for topological superconductivity. Second, we demonstrate how Yu-Shiba-Rusinov states may give rise to a Josephson diode effect in the presence of time-reversal symmetry. To arrive at this conclusion, we develop a general theory of the Josephson diode effect in noise-affected junctions and find a general correspondence principle between current-phase asymmetry and nonreciprocal switching currents versus asymmetric dissipation and nonreciprocal retrapping currents. Third, we develop a comprehensive theory of Majorana qubit readout, including the measurement signal. Surprisingly, there is an optimal coupling to the measurement device provided the readout relies on the time-integrated signal. Finally, we consider the photogalvanic response of Weyl semimetals, detailing how the orientation of the Fermi arc surface states determines the current direction. This is potentially relevant for application in optoelectronics, as the orientation is, in principle, tunable by surface potentials.

Zeit & Ort

09.05.2023 | 14:30

FB - Raum (1.1.16)
Fachbereich Physik, Arnimallee 14, 14195 Berlin