Important ppart of the project is increasing the scientific ability of the participants by getting experience in other institutes. Already conducted research stays are listed in following table.

Short descriptions of the research visits:

Adam Tatar from GUM (Główny Urząd Miar, Poland) and Recep Orhan from TÜBİTAK (TÜRKİYE BİLİMSEL ve TEKNOLOJİK ARAŞTIRMA KURUMU, Turkey) visited NPL (National Physical Laboratory, United Kingdom) where under the guidance of Jonathan Williams several experiments and measurements were conducted. System used by researchers was based on 1 V Josephson junctions array made in AIST (National Institute of Advanced Industrial Science and Technology, 産業技術総合研究所, Japan) and binary bias source designed and build in NPL. The SNS array of 32 767 junctions was used to generate DC signal of maximum voltage 1.08 V and sinewaves of maximum voltage 0.76 V RMS. During the visit researchers checked and calibrated bias source and made precise current/voltage measurements of Shapiro steps – its width and step centre. Different AC quantum voltages were generated. Stable filtered DAC sinewave compared with quantum sinewave was used for AC/DC transfer which was made with Datron 4920 multimeter.

Vitor Cabral from IPQ (Instituto Português da Qualidade) realized training visit in PTB from 17 to 28 of October 2016. The system setup used for the experimental work was an “AC quantum voltmeter” as a standard to calibrate directly an ac source. The reference system was formed by a PTB Josephson array of 10 V with 16 segments which were biased by a set of 4 commercial current sources. This setup forms a Programmable Josephson Voltage Standard which allows a generation of a stepwise sine wave. The source signal under calibration was compared to the Josephson voltage by a sampling process of the differential voltage measured by a commercial ADC. The measurements were conducted in the way to exploring different parameters configuration of the setup (as the sampling rate, number of periods averaged, number of deleted points in the step transitions) in order to observe the repeatability and/or reproducibility of the results, along its work range of voltage and frequency. These experimental work allowed the acquisition of practical knowledge in several operating features of the system as the: operation of the Josephson array by the control of the bias source associated; the way to check and recognize the happening of flux trapped and the process to deal with it, by the heating of the array; the process to measure and optimize the bias current to each segment of the array, the role of the different parameters configuration to define the measurement process and theirs influence in the measurement results.

Javier Díaz de Aguilar Rois from CEM (Centro Español de Metrología) visited NPL. The visit was mainly related on the feasibility of an ac source based on Digital-to-Analog-Converter (DAC) directly corrected by a Programable Josephson Voltage Standard (PJVS). The initial characterization of the system shows the improvement of the incorporation an ultrastable DAC on the system. More work is necessary but preliminary results are very promising to use this configuration as a new standard. This new standard can be also used for the intercomparison of AC quantum standards.

Helge Malmbekk from JV (Justervesenet) visited NPL (National Physical Laboratory, United Kingdom) for two months, from April to May 2016, to study how a programmable Josephson system (PJVS) can be used to calibrate a voltmeter. The main task involved characterizing the properties of several difference amplifiers (AD), which record the difference between a Digital to Analog Converter (DAC) and a step-wise approximated sine wave from the PJVS. The characterization of the ADs was used to determine the uncertainty in transferring the PJVS value to the voltmeter, using the DAC as a real time calibrated transfer standard.

Martin Šíra from CMI (Czech Metrology Insittute) visited PTB (Physikalisch-Technische Bundesanstalt) for three monts, from August to October 2016, to study application of Josephson Arbitrary Waveform System for calibration of digitizers. A special waveform have been prepared with the aim of calibrating a number of digitizer parameters at once. Parameters of the waveform were based on the properties of the JAWS system in PTB. The waveform have been generated by JAWS using three different configurations of chips to get different range of waveform amplitudes. JAWS is the only device capable of generating such a waveform with sufficient precission and stability. The waveform was sampled by selected digitizers. After an extensive data processing of sampled data several digitizer parameters have been obtained and stability and correlation factors of these parameters was estimated. 

Raúl Caballero Santos from CEM (Centro Español de Metrología) visited PTB. The visit was related with the frequency response and stability of Anolog–to-Digital Converters (ADC) using the PTB Josephson Array Waveform Synthesizer (JAWS). This activity has been very successful and the preliminary data obtained are very promising. This characterization will significantly improve the AC metrological application of the ADCs.

Vitor Cabral from IPQ (Instituto Português da Qualidade) visited NPL (National Physical Laboratory, United Kingdom) and studied Josephson Voltage Systems. The system setup used for the experimental work was a “quantum-referenced waveform synthesizer” as a standard to calibrate directly a Voltmeter. The reference system was formed by a Josephson array of 1 V biased by a current source developed by NPL. As transfers standards was used a commercial DAC that was compared to the Josephson voltage by a sampling process of the differential voltage measured by commercial ADC. The signal of the referenced DAC was used as standard signal to be measured by a DATRON 4920 Voltmeter. The measurements were conducted in the way to exploring different configurations of the setup, equipment and/or measurements conditions in order to observe the repeatability and/or reproducibility of the results. These experimental work allowed the acquisition of practical knowledge in several operating features of the system as the: operation of the Josephson array by the control of the bias source associated; the way to check and recognize the happening of flux trapped and the process to deal with it, by the heating of the array; the major role of the control of the synchronism between the different signals to assure the observation of valid data; the influence in the results of the sampling time instant related to its position in the step of the voltage array; the dependence of the system to the interconnections used and to the consequent current flow.

Josef Pribil from BEV (Bundesamt für Eich- und Vermessungswesen) visited PTB (Physikalisch-Technische Bundesanstalt) from 24th to 28th of October 2016. During this week an ac source was calibrated directly with an “AC Quantum Voltmeter”, developed by PTB. The reference signal was created by a 10 V Programmable Josephson Voltage Standard (PJVS), which was biased by a set of 4 commercial current sources. The reference signal was then compared to the signal from the ac source under test by a sampling process of the differential voltage measured by a commercial ADC. The experimental work was carried out in the way to explore different parameters to set up the system (e.g. different ac voltages & frequencies, number of periods averaged, numbers of samples, sampling rate, deleted points of steps in the transition) and how these parameters effect the accuracy of the measurements. In the course of calibrating the ac source with different configuration parameters a lot of practical knowledge was gained operating the AC Quantum Voltmeter, like exploring the upper and lower limits of the measurable ac voltages & frequencies, to recognize and deal with trapped flux, to minimize electromagnetic noise by grounding, shielding and the use of isolated power supplies and optical isolators and how to optimize the measurements by changing the parameters of the system.