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Real-time detection of electron tunnelling in a quantum dot


Nanostructures in which strong (Coulomb) interactions exist between electrons are predicted to exhibit temporal electronic correlations1. Although there is ample experimental evidence that such correlations exist2, electron dynamics in engineered nanostructures have been observed directly only on long timescales3. The faster dynamics associated with electrical currents or charge fluctuations4 are usually inferred from direct (or quasi-direct) current measurements. Recently, interest in electron dynamics has risen, in part owing to the realization that additional information about electronic interactions can be found in the shot noise5 or higher statistical moments6,7 of a direct current. Furthermore, interest in quantum computation has stimulated investigation of quantum bit (qubit) readout techniques8,9, which for many condensed-matter systems ultimately reduces to single-shot measurements of individual electronic charges. Here we report real-time observation of individual electron tunnelling events in a quantum dot using an integrated radio-frequency single-electron transistor10,11. We use electron counting to measure directly the quantum dot's tunnelling rate and the occupational probabilities of its charge state. Our results provide evidence in favour of long (10 µs or more) inelastic scattering times in nearly isolated dots.

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Figure 1: Characterization of RF-SET response.
Figure 2: Time-domain analysis of the RF-SET output for S1.
Figure 3: Comparison of a simple one-state model with the RTS near a charge degeneracy point for S1.
Figure 4: Measurement of non-equilibrium QD charge fluctuations for S2.


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We thank W. L. Wilson, M. Thalakulam, J. Sarkar, R. J. Schoelkopf, D. H. Johnson, D. Natelson, R. M. Westervelt, D. Driscoll and A. C. Gossard for discussions and experimental assistance. This work was supported by the National Science Foundation, the Army Research Office, and the Robert A. Welch Foundation.

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Correspondence to A. J. Rimberg.

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Lu, W., Ji, Z., Pfeiffer, L. et al. Real-time detection of electron tunnelling in a quantum dot. Nature 423, 422–425 (2003).

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