Gate-controlled nanowire Josephson junctions in the microwave regime: Spectroscopy and coherence of harmonic and anharmonic resonators

• Applicants: Professor Dr. Thomas Schäpers; Professor Dr. Martin P. Weides
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2015 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 259125304

The goal of the proposed project is the experimental realization of an electrically-controlled transmon quantum bit (qubit). The quantum bit circuit will be based on superconductor/semiconductor nanowire Josephson junctions, where the critical current is controlled by a bottom gate or alternatively by a side gate electrode. Thus, the gate-controlled nanowire-based junction will serve as field tunable non-linear inductance in the qubit circuit. As for the nanowires, either bulk InAs nanowires or GaAs/InAs core/shell nanowires will be employed. The latter structure would provide an additional in-plane flux control. The characteristic Andreev level splitting in the nanowire Josephson junction, exceeding the qubit energy, protects the qubit from pair breaking excitations. We plan to investigate the nanowire junctions by transport to determine the switching current and its gate voltage tunability. Fundamental aspects of nanowire junctions at microwave frequencies and the potential of nanowires and voltage gating for quantum circuits will be addressed. Combining transport and microwave experiments requires a hybrid circuit layout with removable transport bias electrode embedded in a resonant circuit. Based upon the results from transport and transmission experiments a quantum bit design will be developed. At the final stage of the project, spectroscopic studies of the nanowire transmon qubit will be performed and the coherence will be determined.

• DFG Programme: Research Grants