Storage time of cold Rb atoms in an optical dipole trap formed by a multimode fiber laser

We systematically studied the storage time of Rb87 atoms in an optical dipole trap (ODT) formed by a multimode fiber laser. Storage time is an important parameter in cold atom experiments. If atoms are prepared in the hyperfine state |F=2〉, hyperfine-state-changing collisions can transfer these atoms from |F=2〉 to |F=1〉, whereby the released kinetic energy leads to considerable trap loss. In most ODT experiments, atoms are prepared in the hyperfine state |F=1〉. However, two-photon Raman transitions induced by high-power multimode fiber lasers can optically pump these atoms from |F=1〉 to |F=2〉, and the following hyperfine-state-changing collision results in the trap loss. In this work, our experimental data indicate that both the two-photon Raman transition and the hyperfine-state-changing collision can be inhibited if the atoms are prepared in the single Zeeman sublevel of |F=2,m=2〉 (or |F=2,m=−2〉) and an auxiliary magnetic field is applied.