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We have recently discovered that the driven classical dynamics of a macroscopic mechanical object can be dominated by the quantum statistical fluctuations of tunneling electrons, i.e., by shot noise. Furthermore, coupling between the object and the electrons modifies the electron-electron correlations, resulting in strongly super- and sub-Poissonian current noise. In particular, we have found that a GaAs-based quantum point contact (QPC) can be viewed as a macroscopic mechanical oscillator (a normal mode of the host crystal) whose position is continuously monitored by a mesoscopic electrical detector (the QPC). Furthermore, electrons tunneling through the QPC cause the host crystal to vibrate by means of quantum mechanical backaction. This effect is similar to Brownian motion, in which the motion of a grain of pollen in water is determined by the classical equilibrium statistical fluctuation of molecules. In our case, however, the motion of the oscillator is determined by the quantum non-equilibrium statistical fluctuations of tunneling electrons. Furthermore, the size disparity between the oscillator (a semiconducting chip containing 10^20 atoms) and the source of the fluctuations driving them (fundamental subatomic particles) is truly extreme, and provides a dramatic example of interaction between the quantum and classical worlds.
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