ac Stark shift and multiphotonlike resonances in low-frequency-driven optical lattices

We suggest that Bose-Einstein condensates in optical lattices subjected to ac forcing with a smooth envelope may provide detailed experimental access to multiphotonlike transitions between ac-Stark-shifted Bloch bands. Such transitions correspond to resonances described theoretically by avoided quasienergy crossings. We show that the width of such anticrossings can be inferred from measurements involving asymmetric pulses. We also introduce a pulse tracking strategy for locating the particular driving amplitudes for which resonances occur. Our numerical calculations refer to a currently existing experimental setup [E. Haller, R. Hart, M. J. Mark, J. G. Danzl, L. Reichs\"ollner, and H.-C. N\"agerl, Phys. Rev. Lett. 104, 200403 (2010)].