Towards the Observation of Collective Radiance Phenomena in a One-Dimensional Array of Waveguide-Coupled Atoms with Sub $-\lambda/2$ Spacing

Recently, it has been shown theoretically that the fidelity of photon storage and retrieval in quantum memories scales exponentially better with the number of emitters if one harnesses the collective response of closely spaced atoms ordered in an array [1]. The improved scaling relies on the effect of selective radiance, that is, destructive interference that suppresses scattering into undesired modes. This occurs when the period of an array of emitters is less than half of the atomic resonant wavelength of the probe laser <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(d &lt; \lambda/2)$</tex>. In order to realize this situation, we trap and optically interface laser-cooled cesium atoms using a two-color nanofiber-based dipole trap [2]. It is composed of a blue-detuned partial standing wave and two red-detuned running wave light fields, which counter-propagate in the fiber to compensate the inhomgenous broadening due to the vector light shift [3]. The resulting trapping potential consists of two 1D-arrays of trapping sites on the opposite sides of the nanofiber, where the axial period is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$d\simeq 0.35\lambda$</tex>. Radially, the minima of the trapping potential are located at a distance of 300nm from the fibers surface. We characterize the trap by measuring the trap frequencies, the total number of stored atoms, the fraction of sites filled with a single atom in the collisional blockade regime, and the lifetime of the atoms.