Phys. Rev. Lett. 114, 146805 (2015)

Electrical noise is often an unwanted presence in electronic devices as it can hamper their operation. Fabian Hartmann and colleagues at the University of Würzburg and the University of St. Andrews have now found a way to harness noise, in the form of voltage fluctuations, to produce a direct current in quantum devices. Two semiconductor quantum dots are lithographically defined in an AlGaAs/GaAs heterostructure, separated by a distance of 150 nm. The first one is connected to an electron reservoir in which voltage fluctuations are induced by a noise source. The magnitude of the fluctuations can be controlled by a voltage. The second quantum dot is capacitively coupled to the first one, and connected to two leads in such a way that the flow of electrons from the left lead is unequal compared with that from the right lead.

Random voltage fluctuations experienced by the first quantum dot supply energy, via Coulomb interaction, to electrons in the second quantum dot. Because of the asymmetry in the left and right contacts of the second dot, a direct current — whose magnitude and direction depend on the noise amplitude and that can be controlled by gates — can be measured through the second quantum dot. The maximum current obtained is 10 nA, with a power of up to 24 pW. The researchers suggest that the device concept could potentially be used for energy harvesting at the nanoscale, although at present all measurements have been carried out at 4.2 K.