Anharmonic parametric excitation in optical lattices - art. no. 033403

We study both experimentally and theoretically the losses induced by parame tric excitation in far-off-resonance optical lattices. The atoms confined i n a one-dimensional sinusoidal lattice present an excitation spectrum and d ynamics substantially different from those expected for a harmonic potentia l. We develop a model based on the actual atomic Hamiltonian in the lattice and we introduce semiempirically a broadening of the width of lattice ener gy bands which can physically arise from inhomogeneities and fluctuations o f the lattice, and also from atomic collisions. The position and strength o f the parametric resonances and the evolution of the number of trapped atom s are satisfactorily described by our model.