Nowhere does the divergence of the quantum and classical descriptions of particle motion become more apparent than in quantum tunneling between two regions of classically stable motion. An archetype of such nonclassical motion, studied since the earlies days of quantum mechanics, in tunneling through an energy barrier. In the 1980s a new kind of tunneling was predicted. Called dynamical tunneling, it involves no potential energy barrier, yet a constant of motion other than energy still classically forbids this quantum-allowed motion. This process should occur, e.g., in perodically driven, nonlinear, Hamiltonian systems with one degree of freedom. Such systems may be chaotic, and may contain phase space regions of stable, regular motion embedded in a sea of chaos. Previous studies predicted dynamical tunneling between such stable regions. Here we present the observation of dynamical tunneling of ultra-cold atoms, from a Bose-Einstein condensate, in an amplitude-modulated optical standing wave. Atoms coherently tunnel back and forth between their initial state of oscillatory motion (in an island of regular motion and the state oscillating 180 degrees out of phase with the initial state.
Issue: No. 6842
Pub Type: Journals
BEC, chaos, dynamical tunneling, tunneling