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 0.2 K and the displacement resolution of 10^(-11) m/Hz^(1/2) are limited by the performance of the QPC as a one-dimensional conductor and by the cantilever-QPC capacitive coupling. 
M. Montinaro, A. Mehlin, H. S. Solanki, P. Peddibhotla, S. Mack, D. D.   Awschalom, and M. Poggio
cond-mat.mes-hall