Zero-frequency current noise for the double-tunnel-junction Coulomb blockade

We compute the zero-frequency current noise numerically and in several limits analytically for the Coulomb-blockade problem consisting of two tunnel junctions connected in series. At low temperatures over a wide range of voltages, capacitances, and resistances it is shown that the noise measures the variance in the number of electrons in the region between the two tunnel junctions. The average current, on the other hand, is linearly related to the mean number of electrons for an asymmetric pair of junctions. Thus, the noise provides additional information about transport in these devices which is not available from measuring the current alone.