Beyond effective Hamiltonians: Micromotion of Bose-Einstein condensates in periodically driven optical lattices

We investigate by statistical means a Bose-Einstein condensate held in a one-dimensional optical lattice whose phase undergoes a fast oscillation. The averaged potential experienced by the atoms yields a periodic potential having the same spatial period but with a renormalized depth. However, the atomic dynamics also contains a micromotion whose main features are revealed by a Kolmorogov-Smirnov analysis of the experimental momentum distributions. Furthermore, we discuss the impact of the micromotion on a quench process corresponding to a proper sudden change of the driving amplitude which reverses the curvature of the averaged potential.