Deviations from early--time quasilinear behaviour for the quantum kicked rotor near the classical limit

We present experimental measurements of the mean energy for the atom optics kicked rotor after just two kicks. The energy is found to deviate from the quasi--linear value for small kicking periods. The observed deviation is explained by recent theoretical results which include the effect of a non--uniform initial momentum distribution, previously applied only to systems using much colder atoms than ours.