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

Optical-levitated nanospheres in vacuum have excellent decoupling from environmental fluctuations. This decoupling makes levitated nanospheres a promising candidate for both precision force measurement and strong coupling with other oscillators. In our experiment, we aim to couple a sample of ⁸⁷Rb atoms to a 170 nm diameter nanosphere situated in a separate vacuum chamber. A shared 781nm beam travels through a sample of 87Rb atoms, and then enters a medium finesse optical cavity (F~350) to interact with the nanosphere. The center of mass motion of the nanosphere along the cavity axis will be encoded into the phase of the 781 nm beam’s retro-reflection from the optical cavity to create an optical lattice to both trap and couple to the ⁸⁷Rb atoms. The nanosphere and the atoms will then experience an effective coupling between their COM phonons through their respective optomechanical couplings with the shared 781 nm beam. Using a variety of atom cooling schemes, such as molasses cooling and polarization gradient cooling, the effective coupling could also lead to cooling of the COM motion of the nanosphere. Strong coupling would lead to hybridization of the nanosphere and atom states, possibly allowing the generation of non-classical states of the nanosphere motion by coupling to the internal states of atoms.