Quantum-based voltage metrology with superconducting Josephson devices at NIST

Abstract

Summary form only given. Over the past three decades, the quantum behavior of Josephson junctions has been exploited to improve the accuracy of dc voltage measurements by five orders of magnitude. State-of-the-art precision voltage-standard systems based on arrays of superconductive Josephson junctions can now provide quantum-accurate, intrinsically stable, programmable voltages at amplitudes greater than 10 V for dc voltages and up to 2 V rms for synthesized ac voltages such as sine waves and arbitrary waveforms. Various measurement techniques have been developed for ac measurement applications in the audio-frequency regime and for 60 Hz power metrology. I describe the key developments in Josephson circuits and in measurement techniques, and summarize their current performance and limitations for voltage metrology applications. In particular, I emphasize how the use of quantum-based systems, even when they produce apparently low-uncertainty and reproducible results, does not guarantee that the measurements are accurate. Finally, I briefly summarize how quantum-accurate, arbitrary waveform synthesis is being used to measure Boltzmann's constant by measuring the Johnson noise of a resistor at the triple-point of water, and how a practical electronic primary temperature standard might be realized with a quantum-based Johnson noise thermometer.