Impact of the latest generation of Josephson voltage standards in ac and dc electric metrology

For decades, the quantum behavior of Josephson junctions has been employed as intrinsic standards for voltage metrology. Conventional dc Josephson voltage standards have been the primary standards for voltage, programmable Josephson voltage standards have been implemented in calibration services and precision measurements, such as the Planck constant, and Josephson arbitrary waveform synthesizers have been employed in ac voltage calibrations and precision measurements of the Boltzmann constant. With the anticipated redefinition of the Systeme International d'Unites, all types of Josephson voltage standards will become intrinsic standards and equivalent realizations of the unit volt. Here we review the state-of-the art performance, best practices, and current impact of these systems for various applications, with an emphasis on ac voltage metrology. We explain the limitations of each system, especially regarding the many potential systematic errors that affect their accuracy and performance for specific applications.