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

Abstract

We systematically studied the storage time of 87Rb atoms in an optical dipole trap (ODT) formed by amultimode fiber laser. Storage time is an important parameter in cold atom experiments. If atoms are prepared in the hyper- fine state jF ? 2i, hyperfine-state-changing collisions can transfer these atoms from jF ? 2i to jF ? 1i, whereby the released kinetic energy leads to considerable trap loss. In most ODT experiments, atoms are prepared in the hyperfine state jF ? 1i. However, two-photon Raman transitions induced by high-powermultimode fiber lasers can optically pump these atoms from jF ? 1i to jF ? 2i, 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 sub- level of jF ? 2;m ? 2i (or jF ? 2;m ? −2i) and an auxiliary magnetic field is applied.