Atom optics kicked rotor: experimental evidence for a pendulum   description of the quantum resonance
  We present measurements of the mean energy for an atom optics kicked rotor ensemble close to quantum resonance. Oscillations in the mean energy in this regime are are shown to be in agreement with a quasi--classical pendulum approximation. The period of the oscillations is shown to scale with a single variable, which depends on the number of kicks. 
S. Wayper, M. Sadgrove, W. Simpson, and M.D. Hoogerland