Exploiting the local polarization of strongly confined light for sub-micrometer-resolution internal state preparation and manipulation of cold atoms

A strongly confined light field necessarily exhibits a local polarization that varies on a subwavelength scale. We demonstrate that a single optical mode of this kind can be used to selectively and simultaneously manipulate atomic ensembles that are less than a micron away from each other and equally coupled to the light field. The technique is implemented with an optical nanofiber that provides an evanescent field interface between a strongly guided optical mode and two diametric linear arrays of cesium atoms. Using this single optical mode, the two atomic ensembles can simultaneously be optically pumped to opposite Zeeman states. Moreover, the state-dependent light shifts can be made locally distinct, thereby enabling an independent coherent manipulation of the two ensembles. Our results open a route toward advanced manipulation of atomic samples in nanoscale quantum optics systems.