The Kicked Harper Model
The kicked Harper model is a quantum mechanical system whose dynamics reduces Harper's Hamiltonian to a two-dimensional area-preserving map. Successive iterations appear to be attracted to the neighborhood of stable "islands," showing chaotic transport.
The kicked Harper Hamiltonian has the form
where and is a row of delta functions with period 1. The discrete version, giving the kicked Harper map, is
 R. Artuso, "Kicked Harper Model," Scholarpedia, 6(10), 2011 p. 10462. doi:10.4249/scholarpedia.10462.