A macroscopic mechanical resonator driven by mesoscopic electrical back-action

Systems with coupled mechanical and optical or electrical degrees of freedom(1,2) have fascinating dynamics that, through macroscopic manifestations of quantum behaviour(3), provide new insights into the transition between the classical and quantum worlds. Of particular interest is the back-action of electrons and photons on mechanical oscillators, which can lead to cooling and amplification of mechanical motion(4-6). Furthermore, feedback, which is naturally associated with back-action, has been predicted to have significant consequences for the noise of a detector coupled to a mechanical oscillator(7,8). Recently it has also been demonstrated that such feedback effects lead to strong coupling between single-electron transport and mechanical motion in carbon nanotube nanomechanical resonators(9,10). Here we present noise measurements which show that the mesoscopic back-action of electrons tunnelling through a radio-frequency quantum point contact(11) causes driven vibrations of the host crystal. This effect is a remarkable macroscopic manifestation of microscopic quantum behaviour, where the motion of a mechanical oscillator-the host crystal, which consists of on the order of 10(20) atoms-is determined by statistical fluctuations of tunnelling electrons.