Application of the Josephson effect in electrical metrology

Over the last 30 years, metrology laboratories have used the quantum behavior of the Josephson effect to greatly improve voltage metrology. The following article reviews the history and present status of the research and development for Josephson voltage standards. Specifically, the technology and performance of voltage standards that have quantum accuracy is explained in detail, as is their impact on a wide range of electrical metrology applications, primarily those for dc and ac voltage measurements. The physics of the Josephson effect will be presented and the importance of quantum-based electrical standards will be discussed. A detailed explanation of the operation of the conventional Josephson voltage standard and its use for dc applications will be presented, including a description of the most important results. The latter sections of this paper describe recent efforts to apply the Josephson effect to ac voltage and other electrical metrology applications. Advanced voltage standard systems have been developed that provide new features such as stable, programmable dc voltages and quantum-accurate ac waveform synthesis. The superconducting technology and integrated circuit designs for these systems will be described. Two different systems have dramatically improved precision measurements for audio-frequency voltages and for electric power metrology.