Real-time control of the periodicity of a standing wave: an optical accordion

We report an experimental method to create optical lattices with real-time control of their periodicity. We demonstrate a continuous change of the lattice periodicity from 0.96 $mu$m to 11.2 $mu$m in one second, while the center fringe only moves less than 2.7 $mu$m during the whole process. This provides a powerful tool for controlling ultracold atoms in optical lattices, where small spacing is essential for quantum tunneling, and large spacing enables single-site manipulation and spatially resolved detection.