Quantum nanoelectronics with multi-terminal Josephson junctions: from stencil mask lithography optimization to novel array architectures and phase-biased topological devices

RWTH Publications (RWTH Aachen)

Abstract

The emergence of practical quantum technologies makes research in experimental quantum physics increasingly important. Superconducting nanoelectronic devices are key building blocks in this field, as their superconducting nature enables quantum phenomena to manifest at macroscopic scale. This PhD thesis explores new ways to perform experimental quantum physics with superconducting nanoelectronic devices. Stencil mask lithography is optimized for multi-terminal Josephson junctions to maximize device yield for the experiments. Multi-terminal Josephson junctions are connected to a network, a so-called Josephson junction array, and their behavior, particularly under magnetic fields, is studied. Phase- and gate-control of multi-terminal Josephson junctions with topological insulator weak link material is examined. An in-situ fabrication method for Josephson junction arrays is introduced. This is used to demonstrate the realization of an array with four-terminal Josephson junctions. This array reveals a novel response to magnetic fields, which can be explained theoretically by its lattice geometry. The critical current of the phase-biased multi-terminal Josephson junctions can be controlled by magnetic flux. The introduction of a technique to reliably improve stencil mask yield accelerates the development time of in-situ fabricated superconducting devices. The in-situ fabrication can now also be used to realize Josephson junction arrays, including multi-terminal Josephson junction arrays. The observation of the novel response to magnetic fields of the four-terminal Josephson junction array opens several pathways for scientific exploration in future. This thesis identifies limitations and discusses technical improvements for phase- and gate-control of topological-insulator-based multi-terminal Josephson junctions.

Authors 1

1. Justus Teller corresponding Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen