It is often overlooked that so far, there has been inconsistency between the definition of the ampere in SI units and its realization. For instance, the ampere is defined based on the classical Ampere’s law, while its representation has been made through the Ohm’s law, that is, the ratio of the Josephson voltage to the quantum Hall resistance that do not belong to the SI units. However, in the revised SI units that are slated to take effect in 2019 on World Metrology Day, 20 th of May, it is significant to note that the ampere will be defined as a flow of electrons with the numerical value of the elementary charge fixed. In this instance, all three of the electrical units, such as the current, voltage and resistance will become defined on the basis of quantum physics. As a candidate for the quantum current standard, the various types of single electron pump devices are reviewed in relation to the redefinition of the ampere.

In the current SI (International System of Units), the kilogram is defined by the mass of a material artefact. In this instance, because the artefact can be damaged during use, the present definition is inherently considered unstable. To overcome the shortcomings of the present kilogram definition, the SI will be redefined in near future. In the new SI, the kilogram will be redefined by fixing the numerical value of the Planck constant. After the kilogram redefinition, realization experiments which link the Planck constant to the mass will be necessary. In the new SI, the kilogram will be realized through experiments including the Kibble balance and the X-ray crystal density. The Kibble balance, which is named for the scientist Bryan P. Kibble, is an electromechanical device comparing mechanical power and electrical power. The electrical power is proportional to the Planck constant, because of the voltage and resistance are measured using the Josephson effect and the quantum Hall effect, respectively. The Planck constant is an invariant and not a characteristic of a man-made object, or a specific experiment. The new mass unit is more stable than the current one, and will pave the way for the advancement of precision measurement.