Journal
SUPERCONDUCTOR SCIENCE & TECHNOLOGY
Volume 28, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0953-2048/28/2/025009
Keywords
superconducting qubits; Josephson junctions; flux qubits; pi-junctions; superconductor-ferromagnet junctions
Categories
Funding
- Russian Quantum Center
- Ministry of Education and Science of the Russian Federation [11.G34.31.0062, 2-2014-025]
- Programs of the Russian Academy of Sciences
- Deutsche Forschungsgemeinschaft (DFG)
- State of Baden-Wurttemberg through the DFG Center for Functional Nanostructures (CFN)
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We describe fabrication and testing of composite flux qubits combining Nb-and Al-based superconducting circuit technology. This hybrid approach to making qubits allows for employing p-phase shifters fabricated using well-established Nb-based technology of superconductor-ferromagnet-superconductor Josephson junctions. The important feature here is to obtain high interface transparency between Nb and Al layers without degrading sub-micron shadow mask. We achieve this by in situ Ar etching using e-beam gun. Shadow-evaporated Al/AlOx/Al Josephson junctions with Nb bias pads show the expected current-voltage characteristics with reproducible critical currents. Using this technique, we fabricated composite Nb/Al flux qubits with Nb/CuNi/Nb pi-shifters and measured their magnetic field response. The observed offset between the field responses of the qubits with and without p-junction is attributed to the pi phase shift. The reported approach can be used for implementing a variety of hybrid Nb/Al superconducting quantum circuits.
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