Feedback cooling of cantilever motion using a quantum point contact transducer

We use a quantum point contact (QPC) as a displacement transducer to measure and control the low-temperature thermal motion of a nearby micromechanical cantilever. The QPC is included in an active feedback loop designed to cool the cantilever's fundamental mechanical mode, achieving a squashing of the QPC noise at high gain. The minimum achieved effective mode temperature of 0.2K and the displacement resolution of 10(-11) m/root Hz p are limited by the performance of the QPC as a one-dimensional conductor and by the cantilever-QPC capacitive coupling. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754606]