Highly excited Rydberg atoms are atomic-scale laboratories where the quantum mechanics of chaotic systems can be tested. The extensive symmetry breaking introduced into the Coulomb potential by crossed electric and magnetic fields removes the obstacles for phenomena not possible in 2 degrees of freedom. We bring out the classical structures that support the complexity of motion and lead to alternating layers of order and chaos. The special status assigned to certain dominant periodic orbits by experiment emerges naturally in our treatment.

• Received 31 January 1994

DOI:https://doi.org/10.1103/PhysRevLett.73.2428