Single-electron Counting Device

Single-electron counting device (see a frontispiece) is promising for detecting individual electron flow and analyzing an electrical current with various statistical analyses. Here, we present some experiments as a single-electron ammeter for detecting an extremely faint current and as a physical tool to investigate electron correlation in a transport [1]. Toshimasa Fujisawa

Physical Science Laboratory

We have developed a single-electron counting device, which measures the location of an electron in two quantum dots by using a point contact electrometer (see the frontispiece). For example, an average current can be obtained by counting the number of net electron flow in a given period. We have demonstrated such current measurement on a single-electron transistor as shown in Fig. (a). The obtained current shows Coulomb blockade oscillations as shown in Fig. (b), where noise level of about 3 atto-ampere is three or four orders of magnitudes smaller than that in a conventional ammeter.

In addition to the average current, various statistical analyses are also demonstrated. Figure (c) shows a histogram of the interval between two consecutive forward electron tunneling events (called forward recurrence time), where the reduction of the occurrence with zero interval suggests anti-bunching correlation. This appears from Coulomb interaction in the single-electron transport through the counting device. Moreover, Fig. (d) represents a histogram of the current measured in a short periodT_{avr}(counting statistics), where higher order noise of the current are extracted to characterize the distribution of the current. We believe that various correlated transport can be examined with this technique.[1] T. Fujisawa, et al., Science

312(2006) 1634.

Fig. Experiments on single-electron counting. (a) A circuit diagram for measuring a current from a single-electron transistor. (b) Coulomb blockade oscillations of the device. (c) Anti-bunching correlation in the transport through the device. (d) Counting statistics of the current showing the second (S) and third (C) order noise.

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