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.

We have used the extreme sensitivity of electron tunneling to variations in electrode separation to construct a novel, compact displacement transducer. Electrostatic forces are used to control the separation between the tunneling electrodes, thereby eliminating the need for piezoelectric actuators. The entire structure is composed of micromachined silicon single crystals, including a folded cantilever spring and a tip. Measurements of displacement sensitivity and noise are reported. This device offers a substantial improvement over conventional technology for applications which require compact, highly sensitive transducers.

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.

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