Controlling Condensate Collapse and Expansion with an Optical Feshbach Resonance

We demonstrate control of the collapse and expansion of an Sr88 Bose-Einstein condensate using an optical Feshbach resonance near the S01-P13 intercombination transition at 689 nm. Significant changes in dynamics are caused by modifications of scattering length by up to ±10a_bg, where the background scattering length of Sr88 is a_bg=-2a₀ (1a₀=0.053nm). Changes in scattering length are monitored through changes in the size of the condensate after a time-of-flight measurement. Because the background scattering length is close to zero, blue detuning of the optical Feshbach resonance laser with respect to a photoassociative resonance leads to increased interaction energy and a faster condensate expansion, whereas red detuning triggers a collapse of the condensate. The results are modeled with the time-dependent nonlinear Gross-Pitaevskii equation.