Current measurement by realtime counting of single electrons
Abstract
The fact that electrical current is carried by individual charges has been known for over 100 years, yet this discreteness has not been directly observed so far. Almost all current measurements involve measuring the voltage drop across a resistor, using Ohm's law, in which the discrete nature of charge does not come into play. However, by sending a direct current through a microelectronic circuit with a chain of islands connected by small tunnel junctions, the individual electrons can be observed one by one. The quantum mechanical tunnelling of single charges in this onedimensional array is time correlated, and consequently the detected signal has the average frequency f = I/e, where I is the current and e is the electron charge. Here we report a direct observation of these timecorrelated singleelectron tunnelling oscillations, and show electron counting in the range 5fA1pA. This represents a fundamentally new way to measure extremely small currents, without offset or drift. Moreover, our current measurement, which is based on electron counting, is selfcalibrated, as the measured frequency is related to the current only by a natural constant.
 Publication:

Nature
 Pub Date:
 March 2005
 DOI:
 10.1038/nature03375
 arXiv:
 arXiv:condmat/0411420
 Bibcode:
 2005Natur.434..361B
 Keywords:

 Condensed Matter  Mesoscopic Systems and Quantum Hall Effect
 EPrint:
 9 pages, 4 figures