Cryogen-Free Operation of SNIS for AC Quantum Voltage Standards

Abstract

We report on the recent and ongoing activities on helium-free operation with both types of Josephson standards: programmable SNIS arrays. Helium-free operation provides ease of use, a wider number of applications and users. Moreover, they allow to reduce cable loading thus are then crucial to overcome frequency-related limitations to their ultimate accuracy. Thermalization problems not faced with helium cooling are still challenging, in particular with programmable standards. The higher temperature operation capabilities of SNIS technology is advantageous to simplify cooling issues. Some of our recent results indicate that a careful design of the setup allows operation with short cables without affecting the cooler effectiveness. If confirmed, cryogen-free SNIS Josephson standards will prove a benefit to speed up the synthesized quantum signal frequency rather than another obstacle to overcome.

On the Synthesis of Stepwise Quantum Waves Using a SNIS Programmable Josephson Array in a Cryocooler

“…The cryocooler setup is an improved version of that reported in [14], which was used to test both programmable SNIS array and pulse driven SNS array. It is based on a Gifford-McMahon closed-cycle refrigerator with top loading sample assembly, a minimum temperature near 2.9 K (no thermal load), and nominal cooling power of 1 W at 4.2 K. The cold finger top was fitted with an additional copper disk (cold plate) which contains a thermometer and a heater for temperature monitoring and control.…”

Thermal Performances of an Improved Package for Cryocooled Josephson Standards

“…The PJVS chip used in this experiment was fabricated in cooperation with PTB (Physikalisch-Technische Bundesanstalt) with the Superconductor-Normal-Insulator-Superconductor (SNIS) technology [16], developed for applications in quantum voltage metrology and with peculiar characteristic in terms of reduced temperature dependence of the electrical parameters [17]. Its operation was intensively investigated both in liquid helium and in cryocooler [18], [19]. It is made by 8192 series-connected Nb/Al-AlO x /Nb junctions, which are sub-divided into fourteen individually-biased binary segments.…”

Application and Error Analysis of Differential Sampling for AC Power Measurement based on Quantum Voltage

“…Principle of Pulse Driven AC Josephson Voltage Standard (ACJVS)The pulse-driven AC Josephson Voltage Standard (ACJVS) generates the quantum signal of the synthesized by changing the microwave frequency radiated on the Josephson junction array[12,13]. The pulse-driven quantum voltage reference is based on the Delta-Sigma Modulated analog-to-digital converter.…”

“…Composite schematic diagram of ACJVS.The PJVS array has a more stable performance. The synthesized voltage signal can be used not only as a DC voltage standard but also as an AC voltage standard within 1 kHz and has been used in many AC measurement fields[12][13][14][15]. PJVS is more resistant to current noise and can generate relatively accurate quantized voltage.…”

“…It is difficult to determine the output value of the array voltage during the switching process.The voltage waveform synthesized by the ACJVS system is close to the ideal sine wave. The accuracy of the synthesized voltage is high, the frequency spectrum of the voltage signal is very pure, and the frequency coverage ranges from 150 Hz to 100 kHz[13][14][15]. However, compared with the PJVS system, the microwave pulse bias of the ACJVS system is more complex, and the number of corresponding junctions is much less than the PJVS system, leading to a decrease in the amplitude value of the synthetic voltage.…”