Enhanced laser cooling and state preparation in an optical lattice with a magnetic field

We demonstrate that weak magnetic fields can significantly enhance laser cooling and state 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 reduces 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.