The world's smallest electric motor consisting of only two atoms being powered by quantum noise and a time-dependent sinusoidal magnetic field containing a fundamental and its second harmonic frequency (see also).

A quantum Brownian motor fabricated from a tailored GaAs/AlGaAs heterostructure is able to shuttle electrons quantum mechanically alongside the micrometer-sized ratchet structure. quantum tunneling allows for a characteristic with a current reversal, crossing zero. At this very zero-current temperature the device operates as a quantum refrigerator, separating "hot" electrons from oppositely moving "cold" electrons in absence of a net electric current. (Fig. 34 in Rev. Mod. Phys. 81: 381 [2009]).

Taming Brownian motion with idealized motor designs undergoing directional translational (b) or rotational (a, c) motion by harvesting random collisions with thermal gas particles which are held at two different temperatures. (Fig. 22 in Rev. Mod. Phys. 81:381 [2009]).