Atomtronics-Photonics integration with ultracold strontium atoms

Neutral atoms that are optically trapped using the evanescent fields 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, we trap strontium-88 atoms, an alkaline-earth element, in a state-insensitive, nanofiber-based optical dipole trap using the evanescent fields of an optical nanofiber. Employing a two-color, double magic-wavelength trapping scheme, we realize state-insensitive trapping of the atoms for the kilohertz-wide 1S0−3P1,|m|=1 intercombination transition, which we verify by performing high-resolution spectroscopy for an atom-surface distance of about 300 nm. Alkaline-earth atoms also exhibit nonmagnetic ground states, and their ultranarrow linewidth transitions make them ideal candidates for atomic clocks and precision metrology applications, especially with state-insensitive traps. Additionally, given the low collisional scattering length specific to strontium-88, this work lays the foundation for developing versatile and robust matter-wave atomtronic circuits over nanophotonic waveguides.