Highly uniform submicron junction arrays and applications to next generation photodetectors

Josephson junctions are an ubiquitous circuit element in cQED experiments. In complex devices with many such junctions, such as state-of-the-art microwave photon detectors, precise control over each junction’s critical current is often required, and thus variations of the junction area and tunnel barrier thickness must be sufficiently minimized. Analyzing junction array resistance distributions from many wafers, we have identified several key processing variables to improve uniformity. Using this optimized recipe, we have fabricated and benchmarked a single microwave photon detector utilizing four identical transmons to mediate cross-Kerr coupling between a photon input waveguide and a readout resonator. Plans to increase detector performance by distributing the coupling over 1000’s of junctions will be discussed; a very challenging device to build without the uniformity improvements presented.