Phase-locking of stacked all-niobium junction arrays to external rf-irradiation

We have experimentally investigated the range of locking to external rf-bias current for large 3D arrays. Up to 2000 series connected stacks with two junctions in a stack and 84 series connected stacks with four junctions in a stack were incorporated into a microstripline. Our measurement showed a drastic reduction of the phase locking range with an increasing number of junctions in an individual stack of the array. We investigated the dependence of the attenuation in the microstripline for different numbers of junctions in a stack. In addition, the attenuation of the rf current in the neighboring junctions in a stack was measured.<
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