Josephson voltage standards as toolkit for precision metrological applications at PTB

About 60 years after the discovery of the Josephson effect, electrical DC voltage calibrations are routinely performed worldwide—mostly using automated Josephson voltage standards (JVSs). Nevertheless, the field of electrical quantum voltage metrology is still propagating towards AC applications. In the past 10 years the fabrication of highly integrated arrays containing more than 50 000 or even 300 000 junctions has achieved a very robust level providing highly functional devices. Such reliable Josephson arrays are the basis for many novel applications mainly focussing on precision AC measurements for signal frequencies up to 500 kHz. Two versions of quantum AC standards are being employed. Programmable JVS, based on series arrays divided into subarrays, reach amplitudes up to 20 V and usually are used as quantum voltage reference in measurement systems. Pulse driven arrays reach amplitudes up to 1 V or even 4 V and are typically used as Josephson arbitrary waveform synthesizers. This paper summarizes the principal contributions from Physikalisch-Technische Bundesanstalt to the present state of JVS with particular focus on developments for precision metrological applications and our proof-of-concept demonstrations.