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IEEE Transactions on Applied Superconductivity

Josephson Arbitrary Waveform Synthesis With Multilevel Pulse Biasing

Justus A. Brevik, Nathan E. Flowers-Jacobs, Anna E. Fox, Evan B. Golden, Paul D. Dresselhaus, Samuel P. Benz

Published Feb 1, 2017• 34 citations
Publisher

Abstract

We describe the implementation of new commercial pulse-bias electronics that have enabled an improvement in the generation of quantum-accurate waveforms both with and without low-frequency compensation biases. We have used these electronics to apply a multilevel pulse bias to the Josephson arbitrary waveform synthesizer and have generated, for the first time, a quantum-accurate bipolar sinusoidal waveform without the use of a low-frequency compensation bias current. This uncompensated 1 kHz waveform was synthesized with an rms amplitude of 325 mV and maintained its quantum accuracy over a1.5 mA operating current range. The same technique and equipment was also used to synthesize a quantum-accurate 1 MHz sinusoid with a 1.2 mA operating margin. In addition, we have synthesized a compensated 1 kHz sinusoid with an rms amplitude of 1 V and a 2.7 mA operating margin.

DOI
10.1109/tasc.2017.2662708

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We describe the implementation of new commercial pulse-bias electronics that have enabled an improvement in the generation of quantum-accurate waveforms both with and without low-frequency compensation biases. We have used these electronics to apply a multilevel pulse bias to the Josephson arbitrary waveform synthesizer and have generated, for the first time, a quantum-accurate bipolar sinusoidal waveform without the use of a low-frequency compensation bias current. This uncompensated 1 kHz waveform was synthesized with an rms amplitude of 325 mV and maintained its quantum accuracy over a1.5 mA operating current range. The same technique and equipment was also used to synthesize a quantum-accurate 1 MHz sinusoid with a 1.2 mA operating margin. In addition, we have synthesized a compensated 1 kHz sinusoid with an rms amplitude of 1 V and a 2.7 mA operating margin.
A quantum-accurate waveform with an rms output amplitude of 1 V has been synthesized for the first time. This fourfold increase in voltage over previous systems was achieved through developments and improvements in bias electronics, pulse-bias techniques, Josephson junction array circuit fabrication, and packaging. A recently described ac-coupled bipolar pulse-bias technique was used to bias a superconducting integrated circuit with 25 600 junctions, which are equally divided into four series-connected arrays, into the second quantum state. We describe these advancements and present the measured 1 V spectra for 2 Hz and 10 Hz sine waves that remained quantized over a 0.4 mA current range. We also demonstrate a 2 kHz sine wave produced with another bias technique that requires no compensation current and remains quantized at an rms voltage of 128 mV over a 1 mA current range. Increasing the clock frequency to 19 GHz also allowed us to achieve a maximum rms output voltage for a single array of 330 mV.
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.
An array of Josephson junctions (JJs) was driven with photonically generated current pulses to synthesize a high-fidelity 1 kHz bipolar voltage waveform with a quantum-based amplitude that can be directly related to fundamental constants. A photodiode capable of producing high average photocurrent was used to generate large-amplitude current pulses that were ac-coupled to a JJ array. The resulting bipolar current pulses have enabled the first demonstration of quantum-based bipolar waveform synthesis with an optical drive. We measured the quantum locking range with respect to several operating parameters, including 1.2 mA with respect to a dc bias current applied to the array, confirming the robust synthesis of bipolar waveforms.
Abstract This paper reports on the comparison of two Josephson arbitrary waveform synthesizers for frequencies up to 500 kHz. Both independent pulse-driven Josephson arrays produce a 10 mV RMS sinusoidal voltage. They are alternately connected to an analog-to-digital converter which serves as a transfer standard. The setup is capable to of synthesizing quantum-based waveforms using two different pulse-bias techniques. We use the Zero-Compensation method and a two-pole high-pass filter structure in the pulse-bias configuration of one system (the reference) to minimize the amplitude error for signal frequencies up to 500 kHz. Consequently, we are able to directly detect the high-frequency voltage errors in the other system (the device under test). The setup is used to measure differences between both systems, and the influence of parameter variation on the results with Type A uncertainties of 0.4 µV/V ( k = 1) in measurement times of 60 s. We find that the dominant sources of deviations above 10 kHz can be traced to the influence of the output cabling and the pulse bias on the synthesized voltage signal. Our analysis explains the origin and the reduction of these high-frequency voltage errors.
The performance of the NIST Josephson arbitrary waveform synthesizer has been improved such that it generates a root-mean-square (rms) output voltage of 1 V with an operating current range greater than 2 mA. Our previous 1 V JAWS circuit achieved this same maximum voltage over a current range of 0.4 mA by operating every Josephson junction in its second quantum state. The newest circuit synthesizes 1 V waveforms with the junctions operating in the first quantum state. The voltage per array is doubled because the number of junctions in each array was doubled through the use of improved microwave circuit designs that increased the bias uniformity to the junctions. We describe the circuit improvements and device operation, and we demonstrate the system capabilities by showing measured spectra of a 1 Hz sine wave and a dual-tone waveform. With only two arrays of the new circuit, we also synthesized a 128 mV sine wave without a compensation bias signal, which is one of the bias signals required for achieving 1 V. This is the same rms output voltage achieved with the previous circuit using four arrays.
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.