Josephsonvoltstandarden

The Josephson voltage standard, sometimes referred to as the Josephson voltstandarden in Scandinavian languages, is a quantum electrical standard used to realize and calibrate the volt with extremely high precision. It relies on the AC Josephson effect observed in superconducting Josephson junctions when irradiated with microwave frequency.

The principle rests on the quantization of voltage steps that occur across a Josephson junction under microwave irradiation. The voltage of each step is proportional to the frequency of the applied radiation and fundamental constants, described by V = n h f / (2e), where n is an integer, h is Planck’s constant, and e is the elementary charge. In practice, arrays of many Josephson junctions connected in series are used to reach practical voltage levels, while maintaining the same quantization relation. The result is a highly stable voltage that is intrinsically linked to fundamental constants, providing an absolute reference for calibration.

Realization and operation require cryogenic temperatures to maintain superconductivity and precise microwave control. Modern Josephson voltage standards are implemented in superconducting integrated circuits and are operated in metrology laboratories worldwide. They form part of the chain of calibration instruments for voltmeters and digital multimeters, ensuring traceability to SI units.

Historically, the standard has also been tied to a conventional value of the Josephson constant for practical calibration in many labs, although ongoing updates align realizations with the fixed fundamental constants defined in the contemporary SI system.