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We measured the thermodynamic temperature of the melting point of gallium $T_{\mathrm {Ga}}$ using a Johnson noise thermometer (JNT) with an integrated quantum voltage noise source (IQVNS) as a reference. $T_{\mathrm {Ga}}$ was calculated using the fundamental constants recommended by the Committee on Data for Science and Technology (CODATA) for the revision of the International System of Units (SI). The measured $T_{\mathrm {Ga}}$ is consistent with the value defined in the International Temperature Scale of 1990. [ABSTRACT FROM AUTHOR]

We report on our progress in measuring the Boltzmann’s constant by Johnson noise thermometry (JNT) using an integrated quantum voltage noise source (IQVNS) that is fully implemented with superconducting integrated circuit technology. The IQVNS generates calculable pseudo white noise voltages to calibrate the JNT system. Thermal noise of a resistor placed at the temperature of the triple point of water was measured precisely by the IQVNS-based JNT. We accumulated more than 2000 data points to determine the Boltzmann’s constant. The experimentally obtained Boltzmann’s constant was kexp = 1.3806493 × 10−23 J/K with a relative statistical uncertainty of 8.6 × 10−6, which agreed well with the 2014 Committee on Data for Science and Technology value with a relative offset of +0.6 × 10−6. [ABSTRACT FROM AUTHOR]

The antiperovskite manganese nitride compound Mn3Ag1–xCuxN has a broad resistivity-temperature curve around room temperature that is comparable with the Manganin alloy. This curvature and the peak temperature can be adjusted by codoping with Cu and In or Fe. The drift rate of the resistance value was strongly affected by the condition of the four-terminal contact and the shape of the sample. Samples with spot-welded contacts show lower resistance drift rates than samples with Ag-paste contacts. The four-terminal-shaped sample has a drift rate that is 80 times lower than the normal cuboid-shaped sample. We confirmed that the Mn3AgN sample has a sufficiently low-thermal electromotive force against copper that is less than a few microvolts per kelvin. We expect that this antiperovskite compound could be used as a material for precision resistors and could improve the temperature coefficient of resistors for developing metrology standards. [ABSTRACT FROM PUBLISHER]

We have evaluated the linearity of commercial digital voltmeters (DVMs) using a programmable Josephson voltage standard (PJVS) system. The PJVS system is composed of a 524 288-niobium nitride-based Josephson junction array that has the ability to generate arbitrary output voltages up to 17 V with a resolution of 12 bits. In our system, the junction array is operated in a 10-K compact cooler without a liquid-helium coolant. Up to now, we have succeeded in generating accurate dc voltage levels of up to approximately 13 V using this system. In this paper, we demonstrate our PJVS system as a tool for investigating the linearity characteristics of commercial DVMs, with an accuracy level of 0.1 \mu \textV /V or better, and discuss the uncertainty sources in these measurements. [ABSTRACT FROM PUBLISHER]

We have developed a calibration system for the Zener voltage standards using a programmable Josephson voltage standard (PJVS) for liquid-helium consumption reduction and improvement in the calibration performance. The PJVS array is composed of 524 288 niobium nitride (NbN)-based overdamped Josephson junctions and is cooled by a 10-K compact cooler. To verify the validity of the system, indirect and direct comparisons of the PJVS system and our conventional Josephson voltage standard system have been carried out. As a result, an agreement within a relative expanded uncertainty of 8.4\times 10^-10 was obtained for a nominal voltage of 10 V. We also discuss the uncertainty sources in the calibration of the Zener voltage standards using our PJVS system. [ABSTRACT FROM PUBLISHER]

We performed a detailed evaluation of the temperature coefficient of resistance of manganese nitride antiperovskite compounds, i.e., \Mn3\Ag1 - x\Cux \N, around 23 ^\circ\C. The second-order term of the temperature coefficient \beta was found to show a rough correlation with the Cu content. For a Cu content x = 0.4, the compound \Mn3\Ag0.6\Cu0.4 \N shows the lowest temperature coefficients. The drift rate of the samples was also investigated. The drift rate was suppressed to about 1/30 by higher temperature annealing, and the lowest drift rate was 9.1 (\mu\Omega/\Omega)/year. We expect that this antiperovskite compound will be useful for precision resistors and improve the temperature coefficient of resistors by process optimization so that they can be used to produce standard resistors for example. [ABSTRACT FROM PUBLISHER]

Long integration periods are necessary to reach low uncertainty when measuring temperature through Johnson noise thermometry (JNT). The main goal of the National Institute of Standards and Technology JNT program is to achieve a combined relative uncertainty of 6 \times 10^-6 in the measurement of the water triple point temperature, which, in turn, allows determination of Boltzmann's constant at the same uncertainty. To this end, a four-channel JNT system, which will reduce the measurement period twofold, is being developed with new components, including a switchboard, analog-to-digital converters (ADCs), and a programmable recharging power supply system. A significant source of systematic error that was discovered while implementing the new ADCs is described. New measurements are presented using a doubled ADC sampling rate, which show the potential for higher measurement bandwidth. [ABSTRACT FROM AUTHOR]

A cryogenic current comparator (CCC) is an instrument of great importance in electrical metrology, which provides a ratio of two currents with ultimate accuracy based on superconductivity. It is used for dc resistance calibration in many national metrology institutes. Conventional CCCs consist of multi-turn coils of wire windings, a multi-layered shield of superconductor foils and a separate SQUID sensor. This implementation results in a bulky device too massive to cool with a mechanical cryocooler, making a system inconvenient. A new implementation of CCC, an integrated CCC (ICCC) consisting of thin-film spiral coils, a thin-film superconducting shield and a SQUID sensor integrated on a single chip, enables a user-friendly system operated with a compact cryocooler. Prototype ICCC chips were designed and fabricated by using a superconducting Nb integrated circuit technology with chemical-mechanical polishing. The basic operation of the prototype ICCCs was confirmed by monitoring periodic flux-voltage characteristics of the SQUIDs. [ABSTRACT FROM AUTHOR]

We precisely evaluated a single-chip 10-V programmable Josephson voltage standard (PJVS) system based on a closed-cycle refrigerator by directly comparing it with a conventional Josephson voltage standard system. The PJVS chip fabricated using NbN/TiNx/NbN junction technology was used. The result of the measurement showed a good agreement with a combined standard uncertainty of 3.1 parts in 1010 at 10 V. [ABSTRACT FROM AUTHOR]

Since beginning the construction early in 2005, considerable progress has been made on the watt balance of the Bureau International des Poids et Mesures (BIPM). We have continued the development of a room-temperature version to test the feasibility of simultaneous force and velocity measurements. Preliminary measurements of the voltage-velocity ratio have been carried out with a reproducibility of the order of 1 part in 104. The coil suspension has been improved to reduce the undesired coil movement in the 5 degrees of freedom different from a perfectly vertical movement. Further work on the current source has reduced its long-term drift to a few parts in 109 per minute with a satisfactory short-term stability. A technique needed to separate the voltage induced in the coil from the voltage drop due to the current flow based on the use of a second noninductive coil has been tested. The second coil is now being integrated into the apparatus. Work has started on the geometrical and magnetic characterizations of a large precision solenoid that will become the reference for the magnetic field alignment. The collaboration with a university on the fabrication of our magnetic circuit is being continued. This paper briefly outlines the main ideas of the BIPM watt balance and reports the progress to date. [ABSTRACT FROM AUTHOR]

We report the experimental results on a Josephson junction array (JJA) driven by current pulse trains generated by triggering a photo detector located in a cryostat with an optical comb. The key components in the experimental system are a mode locked fiber laser, a metal-semiconductor-metal (MSM) photoconductive switch, and an overdamped JJA. Optical pulse trains generated at room temperature are transmitted via an optical fiber to the MSM-photo detector installed at 4.2 K, and then converted into electric current pulse trains to drive the overdamped JJA. Quantized voltage steps have been verified at multiples of 10 μV, which agrees with the repetition rate of the pulse laser and the number of Josephson junctions in the JJA. [ABSTRACT FROM AUTHOR]

In this paper, quantized voltage steps were observed by driving an overdamped Josephson junction array (JJA) with current pulse trains. The current pulse trains were generated by triggering a metal-semiconductor-metal photodetector installed close to JJA at 4.2 K with a mode-locked fiber laser. The intervals of the constant voltage steps were 10 μV, which agrees with the repetition frequency of the light source (49.7 MHz) and the number of Josephson junctions (100) in the JJA. This is the first step toward establishing an ac voltage standard at the National Institute of Advanced Industrial Science and Technology. [ABSTRACT FROM AUTHOR]

A NbN-based programmable Josephson voltage standard arrays (PJVAs) have been investigated. We show that these arrays can be utilized for programmable operation up to ±1 V. The results of direct comparisons between the PJVA and a conventional superconductor-insulator-superconductor Josephson array agree at voltages between 0.1 V and 1 V within an uncertainty of better than 1 nV. An indirect comparison via a Zener voltage reference also shows agreement within a 1σ type A uncertainty of 13 nV. [ABSTRACT FROM AUTHOR]