  A double-helix optical trapping potential for cold atoms can be
straightforwardly created inside the evanescent field of an optical nanofiber.
It suffices to send three circularly polarized light fields through the
nanofiber; two counterpropagating and far red-detuned with respect to the
atomic transition and the third far blue-detuned. Assuming realistic
experimental parameters, the transverse confinement of the resulting potential
allows one to reach the one-dimensional regime with cesium atoms for
temperatures of several \muK. Moreover, by locally varying the nanofiber
diameter, the radius and pitch of the double-helix can be modulated, thereby
opening a realm of applications in cold-atom physics.
