Fractional revivals of coherence in quantum mechanical oscillators

A case study is made of the delocalisation and revival dynamics of a contin uously driven quantum pendulum in integrable and near integrable regimes, u tilising the Husimi phase-space distribution function, and an entropy funct ion which measures the degree of localisation. The numerical results can be well understood in terms of a simple model description based on a quasi-en ergy representation. Two important time-scales of the evolution are derived , and the model description appears to remain highly accurate in the region of classical KAM-tori, even in the driven case. (C) 2000 Elsevier Science B.V. All lights reserved.