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Conference on Precision Electromagnetic Measurements

2 Volt pulse-driven josephson arbitrary waveform synthesizer

Nathan E. Flowers-Jacobs, Alain Rüfenacht, Anna E. Fox, Paul D. Dresselhaus, Samuel P. Benz

Published Jul 1, 2016• 22 citations
Publisher

Abstract

We created a Josephson Arbitrary Waveform Synthesizer (JAWS) with a root-mean-square (rms) output magnitude of 2 V. This system is composed of two 1 V chips operating on a cryocooler. By controlling the relative phase of the two chips' output voltage, we add the voltages in quadrature and create rms output voltages between (1+1) V=2 V and (1-1) V=0 V. We use this control to compare the two halves of the system as a function of the relative phase, and measure a difference of 8 parts in 108at a nominal rms amplitude of 1 V and 1 kHz.

DOI
10.1109/cpem.2016.7540601

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Conference on Precision Electromagnetic Measurements•Jul 8, 2024•1 citation
We created a Josephson Arbitrary Waveform Synthesizer (JAWS) with a root-mean-square (rms) output magnitude of 2 V. This system is composed of two 1 V chips operating on a cryocooler. By controlling the relative phase of the two chips' output voltage, we add the voltages in quadrature and create rms output voltages between (1+1) V=2 V and (1-1) V=0 V. We use this control to compare the two halves of the system as a function of the relative phase, and measure a difference of 8 parts in 108at a nominal rms amplitude of 1 V and 1 kHz.
The root-mean-square (rms) output voltage of the NIST Josephson arbitrary waveform synthesizer (JAWS) has been doubled from 1 V to a record 2 V by combining two new 1 V chips on a cryocooler. This higher voltage will improve calibrations of ac thermal voltage converters and precision voltage measurements that require state-of-the-art quantum accuracy, stability, and signal-to-noise ratio. We achieved this increase in output voltage by using four on-chip Wilkinson dividers and eight inner-outer dc blocks, which enable biasing of eight Josephson junction (JJ) arrays with high-speed inputs from only four high-speed pulse generator channels. This approach halves the number of pulse generator channels required in future JAWS systems. We also implemented on-chip superconducting interconnects between JJ arrays, which reduces systematic errors and enables a new modular chip package. Finally, we demonstrate a new technique for measuring and visualizing the operating current range that reduces the measurement time by almost two orders of magnitude and reveals the relationship between distortion in the output spectrum and output pulse sequence errors.
We describe a new generation of Josephson Arbitrary Waveform Synthesizers that generate programmable ac waveforms with an rms amplitude of 3 V and, at 1 kHz, have a quantum locking range greater than 1 rnA. This system has two chips with a total of 204 960 Josephson junctions (JJs) co-located on a cryocooler. To test for systematic errors, we phase-shift by 180° the waveform generated by half the JJs (102 480 JJs) to produce an approximate null. The measured residual of 51 nV rms implies a relative agreement of 3 parts in 108between the two halves of the system.
The output voltage of Josephson arbitrary waveform synthesizers (JAWS) is limited by the number of Josephson junctions (JJs) that can be driven by a single pulse-generator channel. Here, we double the number of JJs driven by one generator channel to 51 200 JJs by distributing the pulse bias between four JJ arrays by use of two layers of Wilkinson dividers. We use this single bias to generate a voltage at 1 kHz with an rms magnitude of 1 V. This voltage is quantum-accurate over an operating current range of 1.4 mA. For comparison, the operating current range of a recent design that uses a single layer of Wilkinson dividers is twice as large, but requires two pulse-bias channels to generate 1 V. We also show that we can recover this performance by incorporating in the pulse generator a finite-impulse response (FIR) filter that acts as an equalizer. The FIR filter creates a custom transfer function that compensates for the bandwidth-limited transfer function of the Wilkinson dividers. Optimizing the FIR filter parameters increases the operating current range from 1.4 to 2.7 mA. This ability to drive additional JJ arrays with a single pulse-generator channel will enable future JAWS chips and systems to achieve significantly larger output voltages. This will increase the voltage range for JAWS calibrations of ac thermal converters and improve precision voltage measurements that require quantum-accurate, stable, and distortion-free waveforms with a large signal-to-noise ratio.
We have recently created a 4 V rms cryocooled JAWS (Josephson Arbitrary Waveform Synthesizer) using 204,960 nearly identical Josephson junctions (JJs) that are embedded in coplanar-wave guides. The JJs are pulse-biased at repetition rates up to 16×109pulses per second to create quantum-accurate, calculable AC waveforms at frequencies from DC to greater than 1 MHz. This system has metrological applications including in precision ac voltage calibrations, comparisons of arbitrary impedances, and ac power measurements.
The Josephson arbitrary waveform synthesizer (JAWS) is a series array of thousands of superconducting Josephson junctions that are biased by current pulses such that the array produces voltage waveforms with quantum accuracy. Intrinsically accurate voltage waveforms synthesized with the quantized pulses from Josephson junctions were first demonstrated in 1996. Ten years later, a commercial ac standard was calibrated at an output root-mean-square (RMS) amplitude of 100 mV with the first practical superconducting digital-to-analog converter. Since then, many different bias techniques, pulse-drive electronics, and device technology have been developed and improved in order to achieve a maximum of 138 mV output RMS voltage per Josephson array. In this paper, we report new bias electronics and demonstrate two new pulse-bias techniques. The first technique has demonstrated 250 mV output RMS voltage per 6400-junction array and may enable a practical 1 V system with only four arrays. The second bias technique reduces inductance-related error signals at the signal frequency and should reduce systematic errors for waveforms with frequencies greater than 1 MHz.
This paper describes the current status of developing Josephson arbitrary waveform synthesizer (JAWS) chips in NIM (National Institute of Metrology, China). The chip has one data input channel and two Josephson junction arrays, each array consisted by 4000 double-stack Nb/NbxSi1–x/Nb junctions. The two arrays were driven with a single pulse-generator channel by using one on-chip Wilkinson power divider and inside/outside DC blocks. Root-mean-square (rms) output magnitude of 300 mV was generated with this JAWS chip.