Abstract

The AC-Stark shift of a set of interfering laser beams together with the Zeeman interaction with external magnetic fields provide flexible mechanisms for coherently controlling atomic wave packets. When detuned far from atomic resonance, these optical lattices can trap cold atoms with minimal dissipation and thus provide an ideal environment for observing quantum coherent phenomena. We consider a one-dimensional lattice of double wells produced by counterpropagating linearly polarized laser beams and a static magnetic field transverse to the laser wave vectors. The distance between the wells is determined by the angle between the beam polarizations and is on the order of the optical wavelength, which is macroscopic when compared to the atomic dimension. As such, an atom that is coherently distributed on both sides of the double wells may be considered to be a “Schrodinger cat.” From an experimental perspective, the double-well potential has a built-in polarization gradient, so that tunneling is accompanied by a precession of the atom’s angular momentum. This provides a label for left/right positions in the double well and allows real-time observation of coherent tunneling as an oscillation in the magnetization—something that is typically not possible in a condensed matter system. In addition, this provides a model system for studying Landau- Zener transitions in a regime far from the semiclassical limit, because the potential surfaces cross near the zero-point energy. This regime forces us to reanalyze a quantitative definition of tunneling.

© 1998 Optical Society of America