Laser cooling of diffraction limited size micromirrors

The prospect of realizing entangled quantum states between macroscopic objects and photons [1] has recently stimulated interest in laser-cooling schemes of macroscopic mechanical resonators [2-5]. We describe passive optical cooling of the Brownian motion of a cantilevered micromirror. Since the cantilever forms one mirror of a confocal Fabry-P\'{e}rot cavity, its mirror end has to be of the size of the optical wavelenght in order to ensure high reflectivity. In our setup, the mirror's size is 2.4$\mu $m and hence in the range of the diffraction limit for 1.3$\mu $m laser light. With its weigth of 11pg it represents the smallest mass cooled so far. The optically induced excitation regime was also explored, opening a path to optically driving nanostructures with high frequency resonances. [1] Marshall et al., Phys. Rev. Lett. \textbf{91}, 130401 (2003). [2] Metzger and Karrai, Nature \textbf{432}, 1002 (2004). [3] Gigan et al., Nature \textbf{444}, 67 (2006). [4] Arcizet et al., Nature \textbf{444}, 71 (2006). [5] Kleckner and Bouwmeester, Nature \textbf{444}, 75 (2006).