Akio Iwasa

Attenuation of microwave filters for single-electron tunneling experiments

Two types of microwave filters, metallic powder filters and a filter using a resistive coaxial cable, were tested. Attenuation of the metallic powder filters using copper or stainless steel (SUS304L) was measured at 300 K, 77 K, and 4.2 K, and it was found that SUS304L powder of nominal 30 /spl mu/m grain size gives best result as the microwave filter for single electron tunneling (SET) experiments. Attenuation of a coaxial filter, or Thermocoax with SMA connectors attached at both ends is larger at low temperatures than that at room temperatures, and the temperature dependence of the attenuation does not agree with Zorins model. The filter arrangement in a cryostat designed for SET experiments, is also reported.

Comparison of a Multichip 10-V Programmable Josephson Voltage Standard System With a Superconductor–Insulator–Superconductor-Based Conventional System

We developed a 10-V dc programmable Josephson voltage standard (PJVS) using a multichip technique. The PJVS was based on NbN/TiNx/NbN junctions and operated using a 10-K compact cryocooler. We carried out an indirect comparison with a superconductor-insulator-superconductor-based conventional Josephson voltage standard (JVS) by measuring the voltage of a 10-V zener diode reference standard. The combined standard uncertainty of the comparison was u c = 0.03 muV(k = 1), and the relative combined standard uncertainty was 3 times10-9.

Ten-volt Josephson junction array

An array of 20144 Josephson junctions divided into four strip line branches has been developed and tested. The array generates quantized voltages up to about 14 V under millimeter-wave irradiation of 90 mW at 92.5 GHz, and will be used in a 10-V voltage standard. >

Single-Chip 10-V Programmable Josephson Voltage Standard System Based on a Refrigerator and Its Precision Evaluation

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.

Practical Analysis of Single Electron Pump with Harmonic Drive

We study a two-gate single electron pump device with harmonic AC gate voltages. We have performed numerical and analytical calculations of quantum correction to a DC current due to the cotunneling phenomena. This correction determines the accuracy of the device in a wide range of parameters (temperature, frequency and amplitude of the gate voltage modulation). We found the crossover from adiabatic transport at lower frequencies f f cr to non-adiabatic transport at higher frequencies f f cr. The crossover frequency f cr = { k BT / (e2/ C) }2 / (AR TC) is argued to be the optimal frequency of the pump operation.

A direct comparison of a 10 V Josephson voltage standard between a refrigerator-based multi-chip programmable system and a conventional system

A multi-chip 10 V programmable Josephson voltage standard (PJVS) system was demonstrated using a closed-cycle refrigerator. We precisely measured the PJVS by a direct comparison measurement with a conventional Josephson voltage standard. The result agreed within a combined standard uncertainty of 3.9 × 10−10 at 10 V.

Use of the Josephoson Junction Array Voltage Standard in Industry

A novel trial for use of a fully automated Josephson-junction-array-voltage-standard (JJAVS) system in industry has been carried out since January 1991. Long-term performance tests show that the JJAVS system is available as an industrial-use voltage standard with an accuracy of 0.01 ppm as well as for use in the national laboratory.

Calibration System for Zener Voltage Standards Using a 10 V Programmable Josephson Voltage Standard at NMIJ

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 524288 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 × 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.

Evaluation of linearity in digital voltmeters using PJVS

We are evaluating the linearity characteristics of digital voltmeters (DVMs) using a programmable Josephson voltage standard (PJVS) system. The PJVS system is composed of a 524 288 junction array and a 10 K compact cooler, which enables to generate an arbitrary output voltage of more than 10 V. The voltage signal output with the PJVS system was applied to DVMs, and the linearity characteristics were investigated based on the reading values of the DVMs. As a result, we found that the linearity characteristics can be evaluated with the expanded uncertainty of 0.1 μV/V or better for the 10 V or smaller ranges.

Development of zener calibration system using 10 V programmable Josephson voltage standard at NMIJ

We are developing a calibration system for Zener voltage standards using a programmable Josephson voltage standard (PJVS) for the purposes of the reduction in liquid-helium consumption and also the improvement of the calibration performance. The PJVS array is composed of total 524 288 NbN-based Josephson junctions and is cooled with a 10 K compact cooler. For verifying the validity of the system, the indirect comparison between the PJVS system and our conventional JVS (CJVS) system has been carried out. As a result, the agreement within the relative expanded uncertainty of 7.8 × 10-9 was obtained. The uncertainty in the calibration of Zener voltage standards using our PJVS system is also discussed.