Perspectives of the generation and measurement of small electric currents

This paper provides a comprehensive overview of the historical background, current status, and future prospects related to the generation and measurement of small electric currents. It specifically caters to nonprofessional readers, with the aim of making the information comprehensible. A range of technologies are introduced, applicable in both basic research and industrial context. Quantum-mechanical approaches have been the focus of extensive efforts in this field, encompassing various types of single-electron pumps and combinations of two other quantum standards: the Josephson voltage standard and the quantized Hall resistance standard. These methods offer a reliable and precise means of generating and measuring small electric currents, minimizing uncertainties. However, operating complex cryogenic systems requires specialized expertise. Alternatively, conventional room-temperature systems are comparatively easier to handle. They employ low-noise amplifiers in conjunction with stable high-value resistors or capacitors charged with voltage ramps. This paper not only examines the characteristics of the both quantum and classical approaches from multiple perspectives but also outlines current and future applications for the generation and measurement of small electric currents.