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Qubits with stacked Josephson junctions

Alexey Ustinov (Karlsruhe Institute of Technology, Germany)

Abstract We explore a novel way of making superconducting quantum circuits by going off-plane from the substrate, namely by stacking Josephson tunnel junctions vertically. This approach allows for fabricating very compact inductors needed in many quantum circuit applications. Other potential advantages are, for example, the reduced stray capacitance of the junction array to the ground, which moves the array resonance modes up in frequency thus avoiding the unwanted resonances in the operation band of the circuit. We developed a fabrication process of stacked Al/AlOx/Al junctions and implemented it for making quarton flux qubits. In the talk I will present measurement results of the fabricated qubit circuits and discuss our approaches to enhance their coherence.