Applications: Metrology

Metrology is the science of precision measurement of physical quantities and has developed a close relationship with superconductivity and superconducting materials, beginning with the discoveries of magnetic flux quantization and the Josephson effects in 1961 and 1962. Programmable Josephson voltage standard systems were first proposed and developed at NIST and are nowadays fully demonstrated in numerous metrology measurements and operated in liquid-cryogen-free refrigerators. A Josephson array device with growing applications to ac voltage metrology has emerged in recent years: the pulse-driven Josephson arbitrary waveform synthesizer. The use of superconductors in solenoids allows current densities to be much higher than for conventional conductors due to zero Joule heating. The Josephson effect has been applied to temperature measurement through the detection of Johnson noise using various superconducting junction-based technologies. The most recent application of Josephson technologies to temperature metrology involves the use of quantum-based reference noise-voltage waveforms synthesized by arrays of Josephson junctions.