Christian Schönenberger

Affiliation: Universität Basel

Research Interests: nanoscience, nanoelectronics, quantum physics, quantum electronics
Title: Nanowire-based semi- and superconducting qubits
Abstract: There are a wide variety of physical qubit realizations even in the solid-state alone: transmon, fluxonium, charge, spin, valley, Andreev, and impurity-based qubits. In the quantum- and nanoelectronics group at the University of Basel, we currently work on a range of qubits realized in InAs and GeSi core shell semiconducting nanowires. We have realized Andreev, spin and gatemon qubits. Since time does not permit to address all our results in one lecture, I will focus on two experiments: a) on a singlet-triplet spin qubit based on a double quantum dot realized in a high-quality InAs nanowire, in which zinc-blende and wurzite segments can be controlled with atomic precission; and b) on Andreev qubits realized in InAs nanowires that are coated by a superconducting Al layer in-situ in order to proximitized InAs. For both cases we demonstrate strong coupling to microwave photons in a coplanar transmission line resonator. In case of the Andreev qubits, we could even demonstrate remote qubit-qubit coupling. For this purpose, we have engineered a dedicated coupler circuit that consist of two capacitively linked λ quarter resonators. This system has two distinct modes, a coupler and a readout mode. If both qubits are tuned into resonance to the coupler mode, qubit-qubit operation is possible without loss to the readout line. The challenge for future applications in this platform lies on reaching a large enough parity protection.