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IEEE International Superconductive Electronics Conference (ISEC)

Towards a He-Free Source of Arbitrary Quantum Voltage Signals

Paolo Durandetto, E. Monticone, Bruno Trinchera, A. Sosso

Published Jun 1, 2017• 0 citations
Publisher

Abstract

The Josephson effect is worldwide exploited as the basis for constant reference voltages in National Metrological Institutes (NMIs) and in industry calibration laboratories. Lately, voltage metrology research has been mainly directed towards the application of Josephson effect for the synthesis of very accurate ac and arbitrary voltage signals: pulse-driven Josephson arrays represent the most promising way for linking ac voltage calibrations to a quantum phenomenon. Furthermore, an easy and secure cooling system based on cryocoolers is desirable in order to allow the spread of Josephson standards outside NMIs. A Gifford-McMahon cryocooler is currently in use at INRiM for the operation of ac-Josephson Voltage Standards (JVSs). We employed pulse-driven JVSs for synthesizing sine waves with frequency in the kHz range and amplitudes in the mV range, with distortion around 80 dBc. In this report we present a detailed description of this technique and of the refrigeration system employed.

DOI
10.1109/isec.2017.8314217

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Measurement Science and Technology•Nov 9, 2022•1 citation
The Josephson effect is worldwide exploited as the basis for constant reference voltages in National Metrological Institutes (NMIs) and in industry calibration laboratories. Lately, voltage metrology research has been mainly directed towards the application of Josephson effect for the synthesis of very accurate ac and arbitrary voltage signals: pulse-driven Josephson arrays represent the most promising way for linking ac voltage calibrations to a quantum phenomenon. Furthermore, an easy and secure cooling system based on cryocoolers is desirable in order to allow the spread of Josephson standards outside NMIs. A Gifford-McMahon cryocooler is currently in use at INRiM for the operation of ac-Josephson Voltage Standards (JVSs). We employed pulse-driven JVSs for synthesizing sine waves with frequency in the kHz range and amplitudes in the mV range, with distortion around 80 dBc. In this report we present a detailed description of this technique and of the refrigeration system employed.
The past few decades have witnessed great progress being made from the first voltage standards based on arrays of Josephson junctions. Continuous improvements in the fabrication process have increased the quality and “user-friendliness” of these superconducting circuits. Combined with the improvements in measuring electronics, the range of applications of Josephson-based measurements with unmatched precision has extended from DC into AC voltage metrology for signal frequencies up to 500 kHz. In this poster we will present several Josephson-based measurement systems developed for metrology applications. Two versions of quantum AC standards will be used as Josephson references: Programmable Josephson Voltage Standards (PJVS), which are based on serial arrays with up to 300,000 Josephson junctions, and pulse-driven arrays with more than 50,000 junctions, typically referred to as Josephson Arbitrary Waveform Synthesizers (JAWS). PJVS can reach amplitudes of up to 80 V, while pulse-driven arrays can reach up to 1 V or even 4 V. The advantage of pulse-driven Josephson voltage standards is that they are ideally suited as quantum-based voltage synthesizers for arbitrary waveforms or sine waves with high spectral purity. Therefore, they can be used directly to characterize or calibrate ADCs. In addition, JAWS are particularly useful in Josephson impedance bridges, which perform automated impedance calibrations at the 10-9 uncertainty level over a wide frequency range from 50 Hz to 80 kHz in a single bridge. We will further show how PJVS are used in commercial quantum voltmeters for DC and AC voltages and are typically used as quantum voltage references in measurement systems. Using differential sampling based on PJVS, uncertainties at the level of a few parts in 108 for frequencies up to the kHz range can be achieved. Such quantum-based AC voltage calibrations are at least 30 times faster than conventional AC-DC transfer and offer even better uncertainties. This idea has been quickly adopted by many National Metrology Institutes to establish such systems for AC voltage calibrations. As an example, the BIPM will now start worldwide onsite comparisons to ensure the uniformity of the new method which we introduced in 2006. But developments continue. Recently, a sub-sampling technique was used to extend the frequency range of the AC quantum voltmeter to up to 100 kHz with uncertainties below 5 parts in 106. In addition, a novel method, also for differential sampling, enables the measurement of arbitrary waveforms and the calibration of specific tones. Our poster will provide an overview of these Josephson-based metrological applications and present the latest developments from this fast-developing area.
The paper is about development of the lumped Josephson junction arrays (JJAs) for the generation of accurate quantum-based ac voltages. By using semiconductor pattern generators, it was possible to synthesize unipolar and bipolar waveforms with amplitudes of almost 10 mV and frequencies of up to 122 kHz. Higher harmonics and other unwanted noise signals were suppressed by -90 dBc. Because of the unique layout of our JJA, it was possible to connect the circuit directly to the ground, thereby eliminating common-mode signals
We demonstrated the operation of pulse-driven Josephson junction arrays (JJAs) for AC voltage standard using a wideband cryo-prober system with a 4-K Gifford-MacMahon (GM) cooler. This unique system was originally developed for high-speed network switch applications of rapid-single-flux-quantum (RSFQ) circuits and enables wideband data transmission at bit rates of higher than 10 Gbps between room-temperature and cryogenic environments. JJA chips were fabricated using NbN-based superconductor-normal metal-superconductor (SNS) junctions. A 5-mm chip was mounted on a 16-mm chip carrier using flip-chip bonding technology for probe contact. To obtain bipolar output voltages, we tried two types of testing based on the AC coupling technique proposed by the National Institute of Standards and Technology (NIST). A pulse pattern generator (PPG) with a large memory of 134 Mbit was used for covering a wide frequency range of output signals. As a result, we succeeded in bipolar operation of the JJA, generating waveforms at frequencies from 60 Hz to several tens of kilo hertz. The maximum rms voltage obtained for a single array was 12.7 mV. The observed spurious level was lower than -93 dBc at 16 kHz.
We present the combination of two Josephson waveform synthesizers to generate waveforms with low harmonic distortion [below$-$110 dBc (carrier)] and amplitudes above the 1-V level. Fast and flexible code programming enables pulse-driven Josephson arrays to synthesize arbitrary waveforms. We have used the pulse-driven system to cancel the harmonic content from the binary array that can reach 1-V amplitudes. The quantum nature of the Josephson synthesizer ensures very stable amplitudes (better than6×10−86 \times 10^{-8}6×10−8) and no frequency drift. This performance, together with the ability to synthesize arbitrary waveforms, can make this synthesizer a relevant tool for characterizing precision electronics and ac voltage metrology.
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.