  We demonstrate experimentally an autonomous nanoscale energy harvester that
utilises the physics of resonant tunnelling quantum dots. Gate defined quantum
dots on GaAs/AlGaAs high-electron-mobility transistors are placed on either
side of a hot electron reservoir. The discrete energy levels of the quantum
dots are tuned to be aligned with low energy electrons on one side and high
energy electrons on the other side of the hot reservoir. The quantum dots thus
act as energy filters and allow for the conversion of heat from the cavity into
electrical power. This energy harvester device, measured at an estimated base
temperature of 75 mK in a He3/He4 dilution refrigerator, can generate a thermal
power of 0.13 fW when the temperature difference across each dot is about 67
mK.
