  We propose a nanowaveguide platform for collective atom-light interaction
through evanescent field coupling. We have developed a 1cm-long silicon nitride
nanowaveguide can use evanescent fields to trap and probe an ensemble of 87Rb
atoms. The waveguide has a sub-micrometer square mode area and was designed
with tapers for high fiber-to-waveguide coupling efficiencies at near-infrared
wavelengths (750nm to 1100nm). Inverse tapers in the platform adiabatically
transfer a weakly guided mode of fiber-coupled light into a strongly guided
mode with an evanescent field to trap atoms and then back to a weakly guided
mode at the other end of the waveguide. The coupling loss is -1dB per facet
(~80% coupling efficiency) at 760nm and 1064nm, which is estimated by a
propagation loss measurement with waveguides of different lengths. The proposed
platform has good thermal conductance and can guide high optical powers for
trapping atoms in ultra-high vacuum. As an intermediate step, we have observed
thermal atom absorption of the evanescent component of a nanowaveguide, and
have demonstrated the U-wire mirror magneto-optical trap that can transfer
atoms to the proximity of the surface.
