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Measuring current by counting electrons in a nanowire quantum dot
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) SEM image of the device. The QD is formed in the nanowire, with the QPC located in the 2DEG directly beneath the QD. (b) Typical time trace of the QPC conductance, showing a few electrons tunneling into and out of the QD. The upper level corresponds to a situation with electrons on the QD. (c) Rise time of the detector, defined as the time needed for the current to cross the midline between current levels belonging to the and electron states.

Image of FIG. 2.
FIG. 2.

(a) Coulomb diamonds measured by counting electrons entering and leaving the QD. To compensate for changes in the QPC potential, we set and . (b) Distribution of tunneling times, taken at the position marked by I in (a). The solid lines are fits to Eq. (1) in the text, with fitting parameters and . [(c) and (d)] , for the upper-middle part of (a). The arrow in (c) marks the position where an excited state enters the transport window. The inset of (d) depicts the energy levels of the system at the position marked by the arrow in (c).

Image of FIG. 3.
FIG. 3.

(a) Electron count rate measured with the QD in a more open regime. (b) QD current for the same region as in (a), measurement with a conventional current meter. (c) Energy level diagrams for the three regions marked in (a). In I, the count rate is due to equilibrium fluctuations between the QD and the drain lead. In region II, transport is blocked due to weak coupling between the QD ground state and the source lead. In III, a more strongly coupled excited state is available for transport and the current through QD is strongly increased. (d) Cross section of the color maps in (a) and (b) taken at . The black curve is the current measured with current meter, while the gray is measured by counting electrons. The dashed line is the counting signal when compensating for the limited bandwidth of the detector.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Measuring current by counting electrons in a nanowire quantum dot