Towards cooling the center of mass motion of a levitated nanosphere with cold atoms

Optically-levitated nanospheres under vacuum have excellent decoupling from fluctuations in their environment. This decoupling makes levitated nanospheres a promising candidate for both precision force measurement and the generation of strong coupling with other oscillators. Access to the strong coupling regime allows our nanosphere to not only couple to cavity photons, but also to cold atoms through the transfer of photons of a shared beam. In our experiment, a shared 781 nm beam will optomechanically couple to a 170 nm diameter nanosphere via a medium finesse cavity (F~250) and exhibits linear coupling when the nanosphere is placed in between the beam’s nodes and antinodes. Its subsequent retro-reflection from the cavity will create an optical lattice that traps a sample of ⁸⁷Rb atoms in a separate vacuum chamber ~ 1 m away. The nanosphere and atoms will then have an effective coupling between their respective COM phonons through their optomechanical couplings with the shared 781 nm beam. Through this effective coupling, well-known atom cooling schemes such as molasses cooling and polarization gradient cooling can sympathetically cool the COM motion of the nanosphere. This hybridized could also be extended to couple the internal states of the atoms to the nanosphere.