QDev Master defence: Thorvald Wadum Larsen – University of Copenhagen

QDev Master defence: Thorvald Wadum Larsen

Superconducting transmon qubits are promising candidates for a scalable quantum processor.
This thesis introduces a gatemon, a hybrid semiconductor-superconductor transmon qubit.
An electrostatic gate controls the Josephson energy of a gatemon qubit by depleting the charge carriers in a semiconductor-based Josephson junction.
We integrate a semiconductor nanowire with an epitaxially grown superconductor shell into a transmonlike circuit forming a gatemon.
Strong coupling to a microwave cavity is observed as a vacuum-Rabi splitting.
Full microwave control of single qubits together with a two-qubit interaction enabled by gate voltage pulses provide a universal gate set in gatemon qubits.
Due to voltage control rather than flux control, dissipation in control lines is reduced.
Furthermore, it is demonstrated that a switchlike, gate-tunable Josephson junction can modulate the resonance of a microwave cavity paving the way for gate tunable qubit-qubit couplings.