Monday 13th March 2023 at 3pm, Çağlar Girit (SPEC, CEA) will give a seminar on Spectroscopy of Topological Josephson Junction Circuits in the Auditorium.
Abstract : Topology, like symmetry, is a fundamental concept in understanding the spectra of physical systems. Non-trivial topological properties of a system may enable applications in fields such as in metrology or quantum information. The most remarkable of these applications is the resistance standard using the quantum Hall effect and the voltage standard using the AC Josephson effect. I present a superconducting circuit with three Josephson tunnel junctions which should have protected degeneracies in the topologically non-trivial regime, much like in a Weyl semimetal. We have fabricated and measured the spectra of both topologically trivial circuits, which are shown to be gapped, and non-trivial circuits, in which the spectra are consistent with gap closing. However, a more detailed model incorporating geometric inductances casts doubt on whether the gap should really be closed in the "non-trivial" regime, and raises the question : when is topological protection really robust ?
