We demonstrate that weak magnetic fields can significantly enhance laser cooling and sate preparation of Cs atoms in a one-dimensional optical lattice. A field parallel to the lattice axis increases the vibrational ground state population of the stretched state |m=F> to 28%. A transverse field ireduces the kinetic temperature. Quantum Monte-Carlo simulations agree with the experiment, and predict 45% ground state population for optimal parallel and transverse fields. Our results show that coherent mixing and local energy relaxation play important roles in laser cooling of large-F atoms.
Physical Review A 57, R705 (1998)