MQV Early-Career Afternoon

Abstract
The fabrication of superconducting qubits and resonators with long coherence times and
high quality factors is an important milestone on the way towards useful quantum processors. Although significant improvements in coherence time have been made over the last years, reaching qubit lifetimes well beyond 100 μs involves careful investigation of all fabrication steps. Here, we demonstrate that such high device qualities can be achieved by a combination of substrate cleaning, etching optimization and post-process sample cleaning. Additionally, we optimize our dry etching, ozone descumming and metal interconnecting processes. Thereby, we reach quality factors well above 3x10^6 for thin-film niobium CPW resonators and qubit life- and coherence times of over 300
μs for transmon qubits.

Short bio
Leon Koch did his bachelors and masters with Dieter Kölle and Reinhold Kleiner at university of Tübingen. Then he joined Stefan Filipps group in July 2020. Currently his research is focusing on improving the coherence times of superconducting qubtis.

Abstract
Control of Quantum bits is a necessity for the overall goal of the community to implement
deterministic quantum computation. Superconducting qubits benefit from being addressable in the microwave regime, where signal generation is commercially well established. I will give an introduction in the control schemes used to control superconducting qubits, and explore the benefits of exploiting the full range of control design.

Short bio
Max Werninghaus received his Masters Degree from the University of Bonn, where he worked in the group of Dieter Meschede on the deterministic control of atoms trapped in an optical lattice. In 2018, he joined Stefan Filipp at IBM Research in Zurich, Switzerland, where he joined the team in the research of quantum computing based on superconducting qubits. In 2021, Max relocated to the new quantum computing group founded by Stefan Filipp at the Walther-Meissner-Institute in Munich, Germany, and finished his PhD work focussing on control of superconducting qubits in November 2022. Currently, he is coordinating the experimental efforts at the WMI under Stefan Filipp. The targets of the WMI quantum computing group include the scaling of superconducting qubit processors to provide a Bavaria-based cloud computing centre with processors with up to 100 qubits.

Relevant publications
https://www.nature.com/articles/s41534-020-00346-2
https://link.aps.org/doi/10.1103/PRXQuantum.2.020324