Optical fibers can be heated and stretched down to radii less than
an optical wavelength, where much of the optical mode extends into the
vacuum. With careful experimental control and understanding of optical
modes, we can create ultrathin fibers that
guide light adiabatically from a core-cladding guided mode onto a
cladding-vacuum mode and back with greater than 99.9% transmission.
Using a variety of diagnostic techniques, we can also launch and
control higher order modes through such fibers, giving new
opportunities for spatially tailoring the evanescent fields. Using an
ultrathin fiber we trap atoms in a two-color evanescent field a few
hundred nanometers from the fiber surface. Such a system is interesting
both as a component of a hybrid quantum system,
and as a one-dimensional atomic system with infinite-range
interactions.