Feedback cooling of the normal modes of a massive electromechanical   system to submillikelvin temperature
  We apply a feedback cooling technique to simultaneously cool the three electromechanical normal modes of the ton-scale resonant-bar gravitational wave detector AURIGA. The measuring system is based on a dc Superconducting Quantum Interference Device (SQUID) amplifier, and the feedback cooling is applied electronically to the input circuit of the SQUID. Starting from a bath temperature of 4.2 K, we achieve a minimum temperature of 0.17 mK for the coolest normal mode. The same technique, implemented in a dedicated experiment at subkelvin bath temperature and with a quantum limited SQUID, could allow to approach the quantum ground state of a kilogram-scale mechanical resonator. 
A. Vinante, M. Bignotto, M. Bonaldi, M. Cerdonio, L. Conti, P.   Falferi, N. Liguori, S. Longo, R. Mezzena, A. Ortolan, G.A....