Towards a quantum ampere with dual-Shapiro steps in ultrasmall Josephson junctions

Microwave-driven ultrasmall Josephson junctions integrated in high-impedance environments exhibit quantized current plateaus, dual of the Shapiro steps observed in conventional Josephson junctions. Dual Shapiro steps were found to agree with the theory in parts in 103, and research is now ongoing with the aim of increasing the plateau currents and robustness, favoring the adoption of dual Josephson devices as primary quantum current standards. This work presents the development of an experimental setup optimized to achieve accurate quantum current plateaus. The setup includes a dry dilution refrigerator equipped with properly filtered DC and microwave lines for the minimization of noise and interferences, targeting the traceable characterization of dual Shapiro steps with uncertainties down to the 10−6 level.