Development and metrological applications of Josephson arrays at PTB

Abstract

The discovery of the Josephson effects 50 years ago initiated a revolution for electrical voltage metrology. This revolution started with single Josephson junctions delivering a few millivolt at most. Meanwhile, highly integrated series arrays containing more than 10 000 or even 300 000 junctions have been developed and fabricated for output voltages up to 10 V. Josephson voltage standards are nowadays used in many laboratories worldwide for dc applications. After their adoption for the representation of the unit of voltage in 1990, the focus of research shifted towards programmable Josephson series arrays. The increasing interest in highly precise ac voltages resulted in new developments for their metrological applications in the last 15 years. This paper summarizes the principal contributions from PTB to the present state of Josephson voltage standards with particular focus on developments and applications for ac standards in metrology and our proof-of-concept demonstrations. The presentation includes the two most promising versions of ac standards, being the programmable Josephson voltage standard based on binary divided series arrays and the Josephson arbitrary waveform synthesizer based on a pulse-driven series array.

An AC Josephson Voltage Standard up to the Kilohertz Range Tested in a Calibration Laboratory

“…It bases on a 10 V programmable Superconductor/Normal metal/Superconductor array manufactured at PTB [11]. A microwave synthesizer delivers a 70-GHz frequency, which is phase locked to an external time base.…”

Stochastic first passage time accelerated with CUDA

“…The numerical experiments have reproduced practical set-ups without extrapolation formulas and could be useful, for instance, to investigate the thermal-quantum transition process. In the same field we suggest that CUDA environment might be also relevant for arrays of Josephson junctions, possibly coupled to a resonator [43] or for voltage standards [44].…”

Maximizing the Resolution of a Dual RF Drive Programmable Josephson Voltage Standard

“…(b) Voltage range, .000 001 V with resolution 1 nV. [11], and PJVS 3 [12] in Table II) but with RF adjustable within 0.4 GHz of the nominal. The PJVSs reported in [10]- [12] have a single RF drive, but the dual RF drive PJVS requires two of these PJVS, either partially or fully utilized.…”