Optical tuning of the scattering length of cold alkaline-earth-metal atoms

It is possible to tune the scattering length for the collision of ultracold ¹S₀ ground-state alkaline-earth-metal atoms using an optical Feshbach resonance. This is achieved with a laser far detuned from an excited molecular level near the frequency of the atomic intercombination ¹S₀-³P₁ transition. Simple resonant-scattering theory, illustrated by the example of ⁴⁰Ca, allows an estimate of the magnitude of the effect. Unlike alkali metal species, large changes of the scattering length are possible while atom loss remains small, because of the very narrow linewidth of the molecular photoassociation transition. This raises prospects for control of atomic interactions for a system without magnetically tunable Feshbach resonance levels.