Quantum standard for amp achieved

A quantum standard for the ampere can now join the ranks alongside the volt and ohm thanks to research from the Physikalisch-Technische Bundesanstalt (PTB). The research team – led by Professor Hans Werner Schumacher – have successful developed a current standard which not only generates a single-clocked electron current, but simultaneously measures this current independently. A quantum standard for the ampere could only be made possible by controlling the capture and release of single electrons in an electronic nano-circuit. Scientists from PTB developed an optimised single-electron pump to allow both the generation of a clocked single-electron current, and its independent measurement with minimum uncertainty. The so-called self-referenced quantum current source is a semiconductor circuit equipped with several pumps and detectors and is operated near absolute zero. The single-electron pump is a minuscule semiconducting island with two current leads. In operation, an electron from the current lead on the left is loaded onto the island and releases into the other lead on the right; if repeated periodically at clock frequency then a current is generated that is only determined by the clock frequency and the singe electron charge “Basically we have taken a pump to handle electrons one by one and added an extra component to overcome statistical errors inherent in these pumps,” Frank Hohls told Laboratory News. “We use several pumps to detect electrons which have left their path and settled on the island. Wehave accounted for these errors and can say a certain number of electrons have been transferred in a certain time.” Schumacher’s group have been able to measure, for the first time, the current involved in each single electron jump. As their pump only transports a few dozen electrons per second, it is slow enough to allow precision measurements. “The process is slow,” Hohls said. “But this first step has demonstrated the principle. Now we will try and make the process faster, in the gigahertz range.” The newly developed source also allows the generation of validated small currents down to the attoampere range – 10^-18 ampere – with a clearly lower measurement uncertainty than possible using conventional current measurement methods. The scientists ­– who published their work on arXiv – have been awarded the Hermann von Helmholtz Prize – a €20,000 prize deemed the most significant in metrology. A self-referenced single-electron quantized-current source