  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 pi-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 pi-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.
