Atom-mediated optical cooling of a mechanical resonator

We present our experimental progress toward the realization of a hybrid quantum system consisting of a high-Q mechanical oscillator coupled to ultracold ${}^{87}$Rb atoms. We observe quality factors and $\omega$-Q products as high as $3 \times 10^{7}$ and $6 \times 10^{13}$ respectively for stoichiometric silicon nitride membranes [1,2] at room temperature, putting us in a regime to achieve quantum ground-state cooling[3]. A novel sympathetic cooling scheme is presented which relies on coupling internal states of ${}^{87}$Rb atoms to the mechanical motion of the resonator via a non-degenerate two-photon Raman process. Proof-of-principle experiments give projected cooling rates of $10^{12}$ phonons/s, leading to the possibility of atom-mediated cooling from room temperature down to the quantum ground state. Our scheme does not rely on the optomechanical system being in the ``good cavity'' regime, thereby enabling the optical cooling of mechanical resonators with low quality factors and poor optical properties such as graphene nanoresonators.\\[4pt] [1] B. M. Zwickl {\em et al}, Appl. Phys. Lett. \textbf{92}, 103125 (2008); \\[0pt] [2] D. J. Wilson {\em et al}, Phys. Rev. Lett. \textbf{103}, 207204 (2009); \\[0pt] [3] F. Marquardt {\em et al}, Phys. Rev. Lett. \textbf{99}, 09390