QDev Seminar: David van Woerkom

QuTech and Kavli Institute of Nanoscience, Delft University of Technology,
2600 GA Delft, The Netherlands

Microwave spectroscopy of Andreev bound states in nanowire Josephson junctions

Semiconducting nanowire Josephson junctions has recently gained interest as building blocks of Majorana circuits [1] and gate-tuneable superconducting qubits [2,3]. We investigate Andreev bound states in InAs/Al core-shell [4] nanowire junctions. We designed and characterized an on-chip microwave circuit coupling the nanowire junction to an Al/AlOx/Al tunnel junction. The tunnel junction emitted photons at frequencies given by the AC Josephson relation [5] to excited the Andreev bound states [6]. Our circuit design allows for voltage, current and phase biasing the nanowire enabling the direct mapping of Andreev bound states. We investigate these Andreev bound states as a function of gate voltage and magnetic field with the ultimate goal of finding Majorana bound states.

[1] Hyart, T., van Heck, B., Fulga, I. C., Burrello, M., Akhmerov, A. R., Beenakker, C. W. J. (2013). Flux-controlled quantum computation with Majorana fermions. Physical Review B, 88(3), 035121.
[2] de Lange, G.,van Heck, B.,Bruno, A., van Woerkom, D.J., Geresdi, A., Plissard, S.R. Bakkers, E. P. A. M., Akhmerov, A.R. ,DiCarlo, L. (2015) Realization of Microwave Quantum Circuits Using Hybrid Superconducting-Semiconducting Nanowire Josephson Elements, Phys. Rev. Lett. 115, 127002
[3] Larsen, T.W.,Petersson, K.D.,Kuemmeth, F.,Jespersen,T.S.,Krogstrup, P.,Nygård, J., Marcus, C.M., (2015) Semiconductor-Nanowire-Based Superconducting Qubit, Phys. Rev. Lett. 115, 127001
[4] Chang, W., Albrecht, S. M., Jespersen, T. S., Kuemmeth, F., Krogstrup, P., Nygård, J., Marcus, C. M. (2015). Hard gap in epitaxial semiconductor–superconductor nanowires. Nature nanotechnology, 10(3), 232-236.
[5] Giaever, I. (1965) “Detection of the AC Josephson effect” Phys. Rev. Lett. 14, 904-906
[6] Bretheau, L., Girit, Ç. Ö., Pothier, H., Esteve, D., & Urbina, C. (2013). Exciting Andreev pairs in a superconducting atomic contact. Nature,499(7458), 312-315.