  Optical control of atomic interactions in a quantum gas is a long-sought goal
of cold atom research. Previous experiments have been hindered by short
lifetimes and parasitic deformation of the trap potential. Here, we develop and
implement a generic scheme for optical control of Feshbach resonance in quantum
gases, which yields long condensate lifetimes sufficient to study equilibrium
and non-equilibrium physics with negligible parasitic dipole force. We show
that fast and local control of interactions leads to intriguing quantum
dynamics in new regimes, highlighted by the formation of van der Waals
molecules and partial collapse of a Bose condensate.
