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Conference on Precision Electromagnetic Measurements

Cryocooler-based quantum voltage standard with dual rf drive

D. Georgakopoulos, Ilya F. Budovsky, Thomas Hagen, Hajime SASAKI, Hirotake Yamamori

Published Jul 1, 2012• 3 citations
Publisher

Abstract

We have developed a Programmable Josephson Voltage Standard (PJVS) that can produce voltages up to 20 V with a resolution of better than 0.1 μV and that does not require liquid helium. The system has two superconductor - normal metal - superconductor junction arrays connected in series and driven by two radiofrequency oscillators. The new system agrees with the primary Josephson voltage standard maintained at the National Measurement Institute, Australia, to within 10 nV.

DOI
10.1109/cpem.2012.6250727

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Superconductor Science and Technology•Feb 1, 2008•15 citations
We have developed a Programmable Josephson Voltage Standard (PJVS) that can produce voltages up to 20 V with a resolution of better than 0.1 μV and that does not require liquid helium. The system has two superconductor - normal metal - superconductor junction arrays connected in series and driven by two radiofrequency oscillators. The new system agrees with the primary Josephson voltage standard maintained at the National Measurement Institute, Australia, to within 10 nV.
We have developed a programmable Josephson voltage standard that can produce voltages up to 20 V with a resolution of better than 0.1 µV over the whole voltage range and better than 1 nV for voltages up to 10 mV. The standard has two superconductor–normal metal–superconductor junction arrays connected in series and driven by two radiofrequency oscillators. The cryogenic part of the standard is based on a cryocooler. The new standard agrees with the primary quantum voltage standard maintained at the National Measurement Institute, Australia, within 10 nV and forms the basis of an automated calibration system for digital multimeters and voltage references.
A compact Programmable Josephson Voltage Standard (PJVS) system based on a cryocooler is under development at the National Institute of Advanced Industrial Science and Technology (AIST). The system uses a 2 V NbN/TiN/NbN PJVS chip operating at 12 K. Since the PJVS chip requires cooling power of less than 100 mW, it is possible to use a compact-size cryocooler, which may be mounted inside a standard 19-inch rack-mount chassis. By combining the 2 V PJVS chip with a high-precision semiconductor voltage multiplier circuit, it is possible to generate arbitrary voltages up to 20 V.
The two main challenges to operating a programmable Josephson voltage standard (PJVS) on a cryocooler are the available cooling power and the temperature oscillations of the cold head. We overcame these challenges and successfully operated a PJVS circuit on a cryocooler by employing one supercritical helium buffer that damps the temperature oscillations, developing a new cryogenic package that increases the thermal conductivity between the chip and the cold head, and increasing overall device performance with fabrication improvements. A 1.32 mA step width of the quantized voltage produced with all of the subarrays of the PJVS circuit biased was achieved at an operating temperature of 4.3 K. The quantum accuracy of the PJVS is maintained at temperatures up to 4.8 K. This result was obtained with a cryocooler that employs a 3 kW water-cooled compressor to produce at the chip about 270 mW of net cooling power at 4.3 K.
We report on the performance of a 1-V dc programmable Josephson voltage standard (PJVS) operating on a commercially available Gifford-McMahon cryocooler at 4 K. The NIST-fabricated niobium superconductor-normal metal-superconductor junction chip has been shown to operate successfully as integrated with this cryopackage, generating 1.229 V at the maximum operating frequency of 19.364 GHz with Shapiro steps at constant voltage that are flat to within less than 100 nV. Because of the large operating margin (greater than 1 mA), these steps were highly stable and immune from noise. Differences in behavior of the PJVS in liquid helium and on the cryocooler are discussed. This demonstration paves the way towards automated warming and cooling of the Josephson device and a fully automated voltage standard system.
Abstract Josephson voltage standards (JVSs) provide a primary realization of the volt, the unit of electromotive force. They generate direct current (dc) voltages up to 10 V and show agreement better than 1 nV V−1 at 10 V. For JVSs based on Josephson junction arrays (JJAs) that are driven by sinusoidal radiofrequency (RF) power, commonly referred to as continuous wave-driven JJAs (CWD JJAs), the minimum voltage that can be generated is limited to the voltage across one Josephson junction (JJ) for practical devices. To achieve this resolution, they may require a perfect JJA chip. JVSs based on a pulse-driven (PD) JJA require high performance electronics (i.e. high bandwidth, low distortion and jitter, pulse shaping filters and large memory) to achieve their minimum and maximum voltage. We have combined two CWD JJAs and two PD JJAs driven by two microwave inputs to one chip to generate quasi-continuous dc voltages up to the sum of the full-scale voltages of both JJAs that are robust to the imperfections of the JJs and have relaxed requirements on the RF electronics driving the JJA, compared to the existing CWD JVSs and PD JVSs, respectively. By use of the JJA chip at the National Measurement Institute Australia, we demonstrate its feasibility to generate voltages up to 1 V. Preliminary evaluation of the system shows that the voltage uncertainty can be 11 nV (k = 2) or better and the theoretical resolution is better than 1 nV from 0 V to 1 V. The main requirement is that all the JJs must have quantum locking ranges with respect to the power and frequency of the RF bias and for the PD JJAs to have a constant voltage over a range of dc bias current. Although this development is not a replacement for existing state-of-the-art JVSs, we anticipate that it will be an alternative fit-for-purpose solution for metrological applications under non-ideal operating conditions or when the components of the state-of-the-art solutions are not available.
We have demonstrated a programmable Josephson voltage standard (PJVS) operation up to 10.84 V using a multi-chip technique. We combined two PJVS chips fabricated using NbN/(TiN x /NbN) 2 junction technology. Each PJVS chip was mounted on a single chip carrier using bonding wire, and the two chip carriers were connected by a simple Cu lead wire, and mounted on a cryocooler. High-precision measurements confirmed flat voltage steps for all 22 cells, with a peak-to-peak variation of 100 nV and wide margins of at least 0.35 mA. We also confirmed the stability of the voltage steps in spite of a temperature and RF frequency variation of ± 0.1 K and ± 0.1 GHz, respectively.