  Single-electron circuits of the future, consisting of a network of quantum
dots, will require a mechanism to transport electrons from one functional part
to another. For example, in a quantum computer[1] decoherence and circuit
complexity can be reduced by separating qubit manipulation from measurement and
by providing some means to transport electrons from one to the other.[2]
Tunnelling between neighbouring dots has been demonstrated[3, 4] with great
control, and the manipulation of electrons in single and double-dot systems is
advancing rapidly.[5-8] For distances greater than a few hundred nanometres
neither free propagation nor tunnelling are viable whilst maintaining
confinement of single electrons. Here we show how a single electron may be
captured in a surface acoustic wave minimum and transferred from one quantum
dot to a second unoccupied dot along a long empty channel. The transfer
direction may be reversed and the same electron moved back and forth over sixty
times without error, a cumulative distance of 0.25 mm. Such on-chip transfer
extends communication between quantum dots to a range that may allow the
integration of discrete quantum information-processing components and devices.
