Chapter Development of Josephson voltage standards

Neurology & clinical neurophysiolog

Development of Josephson voltage standards

Neurology & clinical neurophysiolog

Direct calibration of a true-rms ac voltmeter against a He-free pulsed Josephson standard

Starting from 2019 a new central role is played by quantum standards, owing to the redefined SI, where electrical units are directly linked to the fundamental constants e (elementary charge) and h (Planck constant). Thus, metrologists are nowadays trying to extend the astonishing accuracy attainable in dc measurements to ac and beyond, moving towards calibrations aiming quantum ac voltage generation. Programmable Josephson Voltage Standards are nowadays capable of fulfilling primary metrology requirements only for stepwise-approximated voltage signals up to few hundreds Hz. Pulsed Josephson standards are instead capable of generating arbitrary waveforms at higher frequencies, so are generally called Josephson Arbitrary Waveform Standards (JAWS). Despite of the lower attainable voltage, JAWS are very promising and are the subject of intense research activity. In particular, the capability of generating high spectral purity signals allows high accuracy measurements especially at the low voltage levels (<100 mV rms), which are challenging to be performed by the traditional ac-dc transfer difference using thermal converters. We report in the following about our setup for quantum-based calibrations of a true-rms ac voltmeter with low uncertainty, first results obtained and unsolved issues

Characterization of a Josephson array for pulse-driven voltage standard in a cryocooler

partially_open6sìPulse-driven Josephson junctions allow the synthesis of very precise both spectrally pure and arbitrary wave forms with frequencies up to the megahertz range. We investigated the properties relevant for metrological applications of series arrays with 4000 Josephson junctions fabricated at PTB in cryocooler and liquid helium. DC electrical parameters were evaluated and Shapiro steps dependence on operating conditions was studied. Both cooling techniques provided similar results for all relevant parameters. In particular, we were able to observe Shapiro step widths of more than 1 mA in cryocooler. Yet, we found that some specific effects related to the different thermal conditions must be taken into account for proper operation in cryocooler.openSosso, A.; Durandetto, P.; Trinchera, B.; Kieler, O.; Behr, R.; Kohlmann, J.Sosso, A.; Durandetto, P.; Trinchera, B.; Kieler, O.; Behr, R.; Kohlmann, J

Present and future of high-temperature superconductor quantum-based voltage standards

This paper presents a brief overview of the current state-of-the-art of Josephson junctions for Quantum-based Voltage Standards fabricated with High-Temperature Superconductors (HTS). A short introduction on the history and technical evolution of Low Temperature Superconductors (LTS) technology is provided for non-specialists. Then HTS technology is summarized and discussed in the context of quantum voltage standard applications. Finally, the two most promising technologies: bicrystal and Focused Helium-Ion Beam junctions are discussed with more detail, analyzing strength, limitations and perspectives in both cases

PTB-INRIM comparison of novel digital impedance bridges with graphene impedance quantum standards

This paper describes an onsite comparison of two different digital impedance bridges when performing measurements on a quantum Hall resistance standard with the purpose of realizing the SI unit of capacitance, the farad. In the EMPIR Joint Research Project 18SIB07 GIQS, graphene impedance quantum standards, the Physikalisch-Technische Bundesanstalt (PTB), Germany, developed a Josephson impedance bridge, and the Istituto Nazionale di Ricerca Metrologica (INRIM) and the Politecnico di Torino (POLITO), Italy, developed an electronic digital impedance bridge. The former is based on Josephson waveform generators and the latter on an electronic waveform synthesizer. The INRIM–POLITO impedance bridge was moved to PTB and the two bridges were compared by measuring both temperature-controlled standards and a graphene AC quantized Hall resistance (QHR) standard. The uncertainties for the calibration of 10 nF capacitance standards at 1233 Hz are within 1 × 10−8 for the PTB's bridge and around 1 × 10−7 for the INRIM–POLITO's bridge. The comparison mutually validates the two bridges within the combined uncertainty. The result confirms that digital impedance bridges allow the realization of the SI farad from the QHR with uncertainties comparable with the best calibration capabilities of the BIPM and the major National Metrology Institutes