Two teams of researchers have succeeded in transporting a single electron from one quantum dot to another using a surface wave (Sylvian Hermelin et al. Nature 477, 435–438; 2011 and R. P. G. McNeil et al. Nature 477, 439–442; 2011). This technology could represent an exciting platform for the transfer of quantum-optics experiments to on-chip infrastructures.

Quantum information processing using photons is already a well-developed technology — the key to this steady advance being the fact that photons largely ignore each other. This is in stark contrast to electrons, which, when travelling along a wire, interact with one another and quickly lose any quantum information they might be carrying. However, Hermelin et al. and McNeil et al. have now separately shown how surface acoustic waves can transfer individual electrons over an extended distance while isolating them from their surroundings.

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Gallium arsenide is a piezoelectric material: any mechanical expansion or contraction generates an internal electric field and vice versa. Both groups of researchers used a metallic transducer to generate ripples on gallium arsenide, creating a corresponding propagating electric field. This surface acoustic wave then picked up an electron as it passed across a single-electron source and transported it along a narrow channel to a distant detector.

A natural choice for both a source and a detector of single electrons is a quantum dot. Its small size, usually of the order of ten nanometres, means that the electron energy levels are discrete, much like those in an atom. Thus, electrons can be isolated, and the addition of a single electron leads to a detectable change in a dot's electrical properties.

Hermelin et al. demonstrated a single-electron generation efficiency of 96% and a detection efficiency at the second dot, three micrometres away, of 92%. Such effective processes should aid the scaling up of this basic unit to more complicated circuits. Additionally, McNeil et al. were able to shuttle their electron back and forth between two dots as many as sixty times, clocking up a total distance travelled of 0.25 millimetres.