Implementation of coherent cross junctions for superconducting quantum circuits

Josephson tunnel junctions are the centerpiece of almost any superconducting quantum circuit. By harnessing their nonlinear current-phase relation it is possible to engineer various devices with quantum properties, including superconducting qubits. Typically, the Josephson tunnel junctions for these qubits are fabricated using shadow evaporation techniques. However, lately cross and overlap junctions have gained more and more attention. Compared to shadow mask techniques, neither an angle dependent metal deposition nor free-standing bridges or overlaps are needed. This comes at the cost of breaking the vacuum during fabrication, but simplifies their integration in multi-layered circuits, and on larger substrates. Their implementation in coherent quantum circuits has been demonstrated in a recent work. In this work, we implement cross junctions with superconducting transmon qubits and evaluate qubit coherence properties.