Time ordering and counting statistics

S. Bachmann, G. M. Graf, G. B. Lesovik

Published 2009-07-22, updated 2009-09-21Version 3

The basic quantum mechanical relation between fluctuations of transported charge and current correlators is discussed. It is found that, as a rule, the correlators are to be time-ordered in an unusual way. Instances where the difference with the conventional ordering matters are illustrated by means of a simple scattering model. We apply the results to resolve a discrepancy concerning the third cumulant of charge transport across a quantum point contact.