We have employed a feedback cooling scheme, which combines high-frequency mixing with digital signal processing. The frequency and damping rate of a 2 MHz micromechanical resonator embedded in a dc SQUID are adjusted with the feedback, and active cooling to a temperature of 14.3 mK is demonstrated. This technique can be applied to GHz resonators and allows for flexible control strategies.
@article{arxiv.1106.2106,
title = {Discrete-time quadrature feedback cooling of a radio-frequency mechanical resonator},
author = {M. Poot and S. Etaki and H. Yamaguchi and H. S. J. van der Zant},
journal= {arXiv preprint arXiv:1106.2106},
year = {2012}
}