Large constant voltage generated with a single array including 65 536 Nb/TiN/Nb Josephson junctions

A 2 V Shapiro step with a current height of about 0.3 mA was successfully generated at 4.2 K with a single array including 65 536 Nb/TiN/Nb Josephson junctions under microwave irradiation at 16 GHz. The critical current density was 89 kA cm − 2, and the junction size was 3 µm. The n = 1 step height decreased exponentially as the number of junctions N increased when the number of junctions was less than 30 000, a result that agreed well with the dissipated junction model. On the other hand, the step height was nearly constant when the number of junctions was more than about 30 000, a figure much larger than that theoretically calculated from the model. Using an array including such a large number of Josephson junctions represents a promising way for ac waveform synthesis to increase output voltage to about 1 Vrms.

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