Josephson Voltage Standard Research Articles

Superconducting NbN Nanowires and Coherent Quantum Phase-Slips in DC Transport

A quantum current standard dual to the Josephson voltage standard has been trumpeted as a primary application for the phenomenon of coherent quantum phase-slips (CQPS) in superconducting nanowires, but it requires a dc transport geometry, distinct from the ring geometry in which CQPS have been probed by microwave spectroscopy measurements. We present measurements on NbN nanowires with a width of 15 nm and including integrated thin-film resistors to provide a high-impedance environment. Analysis shows that the nanowire behavior is in line with expectations. The results demonstrate that the process is promising both for future dc transport CQPS measurements and for the fabrication of other circuits in which low-width superconducting nanowires are required.

Uncertainty estimation of non-ideal analog switches using programmable Josephson voltage standards for mutual inductance measurement in the joule balance

Measurement of the mutual inductance is one of the key techniques in the joule balance to determine the Planck constant h, where a standard-square-wave compensation method was proposed to accurately measure the dc value of the mutual inductance. With this method, analog switches are used to compose an analog-switch signal generator to synthesize the excitation and compensation voltages. However, the accuracy of the compensation voltage is influenced by the non-ideal behaviors of analog-switches. In this paper, the effect from these non-ideal switches is analyzed in detail and evaluated with the equivalent circuits. A programmable Josephson voltage standard (PJVS) is used to generate a reference compensation voltage to measure the time integration of the voltage waveform generated by the analog-switch signal generator. Moreover, the effect is also evaluated experimentally by comparing the difference between the mutual inductance measured with the analog-switch signal generator and the value determined by the PJVS-analog-switch generator alternately in the same mutual inductance measurement system. The result shows that the impact of analog switches is 1.97 × 10−7 with an uncertainty of 1.83 × 10−7 (k = 1) and confirms that the analog switch method can be used regularly instead of the PJVS in the mutual inductance measurement for the joule balance experiment.

Comparison of the Josephson Voltage Standards of the DMDM and the BIPM (part of the ongoing BIPM key comparison BIPM.EM-K10.b)

A comparison of the Josephson array voltage standards of the Bureau International des Poids et Mesures (BIPM) and the Directorate of Measures and Precious Metals (DMDM), Belgrade, Serbia, was carried out in June 2015 at the level of 10 V. For this exercise, options A and B of the BIPM.EM-K10.b comparison protocol were applied. Option B required the BIPM to provide a reference voltage for measurement by the DMDM using its Josephson standard with its own measuring device. Option A required the DMDM to provide a reference voltage with its Josephson voltage standard for measurement by the BIPM using an analogue nanovoltmeter and associated measurement loop. Since no sufficiently stable voltage could be achieved in this configuration, a digital detector was used. In all cases the BIPM array was kept floating from ground.The final results were in good agreement within the combined relative standard uncertainty of 1.5 parts in 1010 for the nominal voltage of 10 V.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Comparison of the Josephson Voltage Standards of the NIMT and the BIPM (part of the ongoing BIPM key comparison BIPM.EM-K10.b)

A comparison of the Josephson array voltage standards of the Bureau International des Poids et Mesures (BIPM) and the National Institute of Metrology - (Thailand), NIMT, was carried out in November 2015 at the level of 10 V. For this exercise, options A and B of the BIPM.EM-K10.b comparison protocol were applied. Option B required the BIPM to provide a reference voltage for measurement by the NIMT using its Josephson standard with its own measuring device. Option A required the NIMT to provide a reference voltage with its Josephson voltage standard for measurement by the BIPM using an analogue nanovoltmeter and associated measurement loop. In all cases the BIPM array was kept floating from ground.The final results were in good agreement within the combined relative standard uncertainty of 2.6 parts in 1010 for the nominal voltage of 10 V.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The 2014 North American Josephson Voltage Interlaboratory Comparison

Abstract:The 10th North American Josephson voltage standard (JVS) interlaboratory comparison (ILC) at 10 V was completed in 2014. This ILC was unique because it consisted of two parts. An on-site comparison was conducted between the National Institute of Standards and Technology (NIST) transportable JVS and the pivot laboratory's conventional JVS (CJVS) system. A set of four traveling Zener voltage standards then served to transfer traceability from the pivot laboratory to the 12 other participants. In addition to the regular ILC activities, a second on-site comparison was conducted between the NIST transportable JVS and the programmable JVS (PJVS) provided by the National Aeronautics and Space Administration (NASA). Due to limited availability of the PJVS, only two laboratories were selected to make direct comparisons between their CJVS systems and NASA's PJVS. The method has been used for the first time in the JVS ILC and has the advantage of using the PJVS as a transfer standard. This allowed the parti...

Application of a 10 V Programmable Josephson Voltage Standard in Direct Comparison With Conventional Josephson Voltage Standards

This paper briefly describes the working principle of the 10 V programmable Josephson voltage standard (PJVS) that was developed at the National Institute of Standards and Technology and how to use it in a direct comparison with a conventional Josephson voltage standard (CJVS). Manual and automatic comparison methods were developed to verify the agreement between the two types of Josephson standards. A 10 V PJVS provided by the National Aeronautics and Space Administration (NASA) was used as a transfer standard in the 2014 Josephson voltage standard Interlaboratory Comparison that is organized by the National Conference of Standards Laboratories International. The results of automatic direct comparisons between a NASA PJVS and three CJVSs are reported. Allan variance is applied to analyze the large number of correlated data for Type A uncertainty.

Precision square waves synthesized by programmable Josephson voltage standards for induced voltage compensation in a Joule balance

A programmable Josephson voltage standard (PJVS) can be used to generate a precision square wave for induced voltage compensation to measure the mutual inductance between the coils in a joule balance. In this paper, the influence of the transitions between quantized voltages in the synthesized square waves is analyzed in detail. The ratio of the time-integrated value of the transitions to the total waveform is reduced to several parts in 104 to improve the measurement accuracy. The influence of different configurations of the integrating digitizer is discussed. The result shows that when the voltages are in a quantum state, the time-integrated agreement between the measured and theoretical differences for two PJVS systems is within 4 × 10−9 V s V−1 s−1. For the total time integration of a voltage waveform larger than 2 V s, the combined relative uncertainty is less than 5.9 × 10−8 V s V−1 s−1. The result confirms the capability of the PJVS to generate a precision square wave for the joule balance.

Direct comparison of a 1 V Josephson arbitrary waveform synthesizer and an ac quantum voltmeter

AC Josephson voltage standards based on pulse-driven Josephson arrays (Josephson arbitrary waveform synthesizer—JAWS) have recently achieved an output voltage of at least 1 V root-mean-square. An ac quantum voltmeter (ac-QVM) based on a 2 V programmable Josephson array has been used to verify the quantization level of the new JAWS by performing a direct comparison in the frequency range from 30 Hz to 2 kHz. The comparison has demonstrated an excellent agreement between the two quantum standards of better than 1 part in 108. Sources for systematic errors have been investigated. The overall uncertainty is found to be better than 1.2 parts in 108 (k = 1) for measurements at a frequency of 250 Hz and 1 V amplitude.

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

A dual radio frequency drive programmable Josephson voltage standard can generate quasi-continuous voltages with quantum accuracy. This paper focuses on the mathematical methods used to maximize the achievable voltage resolution and describes two algorithms that can be employed. Quasi-continuous voltages with a resolution of a few nanovolts have been achieved using Josephson junction arrays with missing junctions and an almost arbitrary segment structure.

Bilateral Comparison of 1 V and 10 V Standards between the SMD (Belgium) and the BIPM October to December 2014 (part of the ongoing BIPM key comparison BIPM.EM-K11.a and b)

As part of the ongoing BIPM key comparison BIPM.EM-K11.a and b, a comparison of the 1 V and 10 V voltage reference standards of the BIPM and the Service Métrologie—Metrologische Dienst (SMD), Brussel, Belgium, was carried out from October to November 2014. Two BIPM Zener diode-based travelling standards (Fluke 732B), BIPM_4 (Z4) and BIPM_5 (Z5), were transported by freight to SMD and also back to BIPM. At SMD, the reference standard for DC voltage is a Josephson Voltage Standard (JVS). The output EMF (Electromotive Force) of each travelling standard was measured by direct comparison with the primary standard.At the BIPM, the travelling standards were calibrated, before and after the measurements at SMD, with the Josephson Voltage Standard. Results of all measurements were corrected for the dependence of the output voltages of the Zener standards on internal temperature and ambient atmospheric pressure.The final result of the comparison is presented as the difference between the values assigned toDC voltage standards by SMD, at the level of 1.018 V and 10 V, at SMD, USMD, and those assigned by the BIPM, at the BIPM, UBIPM, at the reference date of 5 November 2014.USMD − UBIPM = 0.14 mV; uc = 0.07 mV, at 1 VUSMD − UBIPM = 0.09 mV; uc = 0.49 mV , at 10 Vwhere uc is the combined standard uncertainty associated with the measured difference, including the uncertainty of the representation of the volt at the BIPM and at SMD, based on KJ-90, and the uncertainty related to the comparison.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Comparison of the Josephson Voltage Standards of the PTB and the BIPM (part of the ongoing BIPM key comparison BIPM.EM-K10.b)

A comparison of the Josephson array voltage standards of the Bureau International des Poids et Mesures (BIPM) and the Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany, was carried out in October 2014 at the level of 10 V. For this exercise, options A and B of the BIPM.EM-K10.b comparison protocol were applied. Option B required the BIPM to provide a reference voltage for measurement by PTB using its Josephson standard with its own measuring device. Option A required PTB to provide a reference voltage with its Josephson voltage standard for measurement by the BIPM using an analogue nanovoltmeter and associated measurement loop.The final results were in good agreement within the combined relative standard uncertainty of 3.9 parts in 1011 for the nominal voltage of 10 V.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Comparison of the Josephson Voltage Standards of the INM and the BIPM (part of the ongoing BIPM key comparison BIPM.EM-K10.b)

A comparison of the Josephson array voltage standards of the Bureau International des Poids et Mesures (BIPM) and the Institutul National de Metrologie (INM), Bucuresti, Romania, was carried out in June 2014 at the level of 10 V. For this exercise, options A and B of the BIPM.EM-K10.b comparison protocol were applied. Option B required the BIPM to provide a reference voltage for measurement by INM using its Josephson standard with its own measuring device. Option A required INM to provide a reference voltage with its Josephson voltage standard for measurement by the BIPM using an analogue nanovoltmeter and associated measurement loop. Since no sufficiently stable voltage could be achieved in this configuration, a digital detector was used. In all cases the BIPM array was kept floating from ground.The final results were in good agreement within the combined relative standard uncertainty of 2.6 parts in 1010 for the nominal voltage of 10 V.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Final Report Key Comparison COOMET.EM.BIPM-K10.b Comparison of the 10 V Josephson Voltage Standards COOMET 542/RU/11

The 10 V Josephson voltage standard of BelGIM was compared with the similar standard of VNIIM in August-November 2014 in accordance with the option B of the BIPM.EM-K10.b comparison protocol. The standard of VNIIM based upon the Josephson effect was used as a transfer standard to measure the output voltage by BelGIM. The final results are in very good agreement with the reference value supplied by the BIPM voltage standard: the relative voltage difference was 6·10-12 at the combined relative standard uncertainty of 2.8·10-10 for the nominal voltage of 10 V.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Traceability of DC high voltage measurements using the Josephson voltage standard

This paper introduces a new methodology for obtaining high voltage DC measurements traceability to the International System of Units (SI) at the Egyptian National Institute for Standards (NIS). The traceability has been achieved via the NIS automated 10 V DC Josephson Voltage Standard (JVS). A 100kV DC voltage divider with a nominal voltage ratio of 10,000:1 is being used with its display in parallel with a high sensitive digital voltmeter. The traceability has been realized by calibrating this digital voltmeter via the JVS system and then it has been used to calibrate the divider display readings. Moreover, the divider ratio has been accurately calibrated using a traceable calibrator source on its high voltage side and the calibrated digital voltmeter on its low voltage side. Accurate and traceable high voltage values have been obtained associated with their expanded uncertainties. Highly improved uncertainties have been achieved using this new calibration technique.

Cryocooler operation of SNIS Josephson arrays for AC Voltage standards

Avoiding liquid helium is now a worldwide issue, thus cryocooler operation is becoming mandatory for a wider use of superconductive electronics. Josephson voltage standards hold a peculiar position among superconducting devices, as they are in use in high precision voltage metrology since decades. Higher temperature operation would reduce the refrigerator size and complexity, however, arrays of Josephson junctions made with high temperature superconductors for voltage standard applications are not to date available. The SNIS (Superconductor-Normal metal-Insulator-Superconductor) junction technology developed at INRIM, based on low temperature superconductors, but capable of operation well above liquid helium temperature, is interesting for application to a compact cryocooled standard, allowing to set a compromise between device and refrigerator requirements. In this work, the behavior of SNIS devices cooled with a closed-cycle refrigerator has been investigated, both in DC and under RF irradiation. Issues related to thermal design of the apparatus to solve specific problems not faced with liquid coolants, like reduced cooling power and minimization of thermal gradients for uniform operation of the chip are discussed in detail.

極低温技術を用いた電気標準の現状

極低温技術を用いた電気標準の現状

Comparison of the Josephson Voltage Standards of the NIM and the BIPM (part of the ongoing BIPM key comparison BIPM.EM-K10.b)

A comparison of the Josephson array voltage standards of the Bureau International des Poids et Mesures (BIPM) and the National Metrology Institute (NIM), Beijing, People's Republic of China, was carried out in November 2013 at the level of 10 V. For this exercise, options A and B of the BIPM.EM-K10.b comparison protocol were applied. Option B required the BIPM to provide a reference voltage for measurement by NIM using its Josephson standard with its own measuring device. Option A required NIM to provide a reference voltage for measurement by the BIPM using its analogue detector and associated measurement loop. In both cases the BIPM array was kept floating from ground.The final results were in good agreement within the combined relative standard uncertainty of 9.2 parts in 1011 for the nominal voltage of 10 V.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Direct comparison of two NIST PJVS systems at 10 V

Two NIST programmable Josephson voltage standard (PJVS) systems are directly compared at 10 V using different nanovoltmeters. These PJVS systems use arrays of triple-stacked superconducting niobium Josephson junctions with barriers made of niobium silicide. Compared with the voltages produced by Josephson voltage standards based on hysteretic junctions, PJVS systems using damped junctions produce predictable voltage levels. However, in order to guarantee the quantization of the voltages and to minimize the errors at the room-temperature voltage output, additional precautions are required. We report several experimental results of voltage measurements that contain significant systematic errors. The generated voltages appear reproducible but they are, in fact, inaccurate. When proper measurement procedures are followed, the results of a direct comparison using an analogue detector show that the two independent PJVS systems agree within 2.6 parts in 1011 at 10 V with a relative total combined uncertainty of 3.4 parts in 1011 (k = 1). Investigations show that the largest systematic error and most significant contribution to the uncertainty budget is caused by the leakage resistance of each PJVS to ground. This paper describes a measurement procedure to characterize this leakage resistance and one approach to including the resulting voltage error in the uncertainty budget.

The North American Josephson Voltage Interlaboratory Comparison

The ninth North American Josephson voltage standard (JVS) interlaboratory comparison (ILC) at 10 V was completed in 2011. An on-site comparison was conducted between the National Institute of Standards and Technology compact JVS and the pivot laboratory system. A set of four traveling Zener voltage standards was then shipped from the pivot laboratory to the other participants. We give the results from the 2011 ILC and review recent comparisons which have used the same traveling standards and similar procedures.

Quantum Calibration System for Digital Voltmeters at Voltages from 10 nV to 1 kV

We have developed a programmable Josephson voltage standard that can generate voltages up to 20 V with a resolution of 10 nV. The standard has two superconductor–normal metal-superconductor junction arrays connected in series and driven by two radio frequency oscillators. The standard has been integrated into a digital voltmeter calibration system for voltages from 10 nV up to 1000 V. The expanded uncertainty $(k = 2)$ of the system is approximately 10 nV for voltages up to 20 V and 0.9 $\mu\hbox{V/V}$ in the voltage range from 20 to 1000 V.