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Conference on Precision Electromagnetic Measurements

Radio-Frequency Waveform Synthesis with the Josephson Arbitrary Waveform Synthesizer

Justus A. Brevik, Christine A. Donnelly, Nathan E. Flowers-Jacobs, Anna E. Fox, P. F. Hopkins, Paul D. Dresselhaus, Samuel P. Benz

Published Jul 1, 2018• 5 citations
Publisher

Abstract

We have measured the output power versus synthesis frequency (transfer function), up to 100 MHz, of a modified Josephson arbitrary waveform synthesizer. A 50 Ω resistor was integrated within the Josephson junction array circuit to match the nominally zero array impedance to a 50 Ω transmission line and load. The resistor significantly reduces ripple in the transfer function due to reflections from impedance mismatches, but it reduces the output voltage by a factor of two. The measured power is constant within 0.01 dB up to 10 MHz, above which it deviates by no more than 0.15 dB.

DOI
10.1109/cpem.2018.8501023

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We have developed a Josephson digital-to-analog converter, otherwise know as a Josephson arbitrary waveform synthesizer, with 300 mV peak output voltage. This is the first system of its kind with demonstrated quantum accuracy. We show precision synthesized waveforms from dc to 100 kHz with measured distortion and harmonic content below 115 dBc (dB below the carrier or fundamental). The heart of the system is a superconducting microwave integrated circuit with two Josephson junction arrays biased in parallel for the microwave drive and connected in series to double the voltage for the audio frequency output waveforms. New superconducting integrated circuits with twice as many stacked junctions and improved microwave circuits have allowed us to more than double the output voltage of our recent system. We also demonstrate that quantum-based synthesized arbitrary waveforms (not just sine waves) can be used for precision measurements of a high-performance commercial analog-to-digital converter.
To make the experimental setup of the Josephson arbitrary waveform synthesizer less complex by reducing the number of RF cables between room and cryogenic temperature, we developed on-chip RF power dividers. By integration of these components, we can eventually increase the number of Josephson junctions operated by one single pulse-pattern generator channel, and thus reduce the costs of the setup. At Physikalisch-Technische Bundesanstalt, we designed, fabricated, and investigated the performance of two different RF power dividers types: the serial-parallel and the Wilkinson power divider. Spectrally pure sinusoidal waveforms were successfully synthesized with both types of power dividers. With the Wilkinson power divider, we obtained 17.55 mV (rms) at a clock frequency of 15 GHz combined with a test array of 1000 Josephson junctions. As for the serial-parallel power divider combined with a test array of 2000 Josephson junctions, we synthesized rms output voltages of 19.0 mV.
We review our development of Josephson-junction-based programmable reference sources to synthesize spectrally pure waveforms with quantum-based voltage accuracy for characterizing and improving future communication devices and systems. The goal is to provide sources that together span the entire radio frequency band, equivalent to seven orders of magnitude in frequency (20 kHz to 300 GHz). To synthesize waveforms in the microwave frequency band, we are extending the existing Josephson arbitrary waveform synthesizer (JAWS) technology used for ac voltage metrology at audio frequencies (<;20 kHz). Using new microwave circuits and experimental techniques, we demonstrate JAWS-based synthesis of single-tone waveforms at 1 GHz, with -49 dBm output power and 79 dBc spur-free dynamic range (SFDR). To synthesize waveforms in the millimeter-wave frequency band, we are exploiting single flux quantum (SFQ) superconducting digital technology to design circuits that amplify SFQ pulses using a network of pulse splitters. With our initial SFQ-based circuit, we demonstrate synthesis of a 4-GHz sine wave with -74 dBm output power and 70 dBc SFDR.
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