  The evanescent field surrounding nano-scale optical waveguides offers an
efficient interface between light and mesoscopic ensembles of neutral atoms.
However, the thermal motion of trapped atoms, combined with the strong radial
gradients of the guided light, leads to a time-modulated coupling between atoms
and the light mode, thus giving rise to additional noise and motional dephasing
of collective states. Here, we present a dipole force free scheme for coupling
of the radial motional states, utilizing the strong intensity gradient of the
guided mode and demonstrate all-optical coupling of the cesium hyperfine ground
states and motional sideband transitions. We utilize this to prolong the trap
lifetime of an atomic ensemble by Raman sideband cooling of the radial motion,
which has not been demonstrated in nano-optical structures previously. Our work
points towards full and independent control of internal and external atomic
degrees of freedom using guided light modes only.
