State-Insensitive Trapping of Alkaline-Earth Atoms in a Nanofiber-Based Optical Dipole Trap

Neutral atoms that are trapped and optically interfaced using the evanescent field surrounding optical nanofibers are a promising platform for developing quantum technologies and exploring fundamental science, such as quantum networks and many-body physics of interacting photons. Building on the successful advancements with trapped alkali atoms, here we demonstrate a state-insensitive, nanofiber-based optical dipole trap for strontium-88, an alkaline-earth atom, using the evanescent fields of an optical nanofiber. Employing a two-color, double magic-wavelength trapping scheme, we realize state-insensitive trapping for the kilohertz-wide intercombination transition, which we verify by performing high-resolution spectroscopy for an atom-surface distance of only 300 nm. This allows us to experimentally find and verify the state-insensitivity of the trap nearby a theoretically predicted magic wavelength of 435.827(25) nm. Given the non-magnetic ground state and low collisional scattering length of strontium-88, this work also lays the foundation for developing versatile and robust matter-wave atomtronic circuits over nanophotonic waveguides.