A proposal for ac magnetic guide and trap of cold atoms

We propose a novel ac electro-magnetic wave guide for cold neutral atoms in an Ioffe tube, which is based on the interaction of a magnetic dipole mome nt of a guided atom with both an ac quadrupole magnetic field in the transv erse direction and a de-bias magnetic field along the guiding axis. The tim e-averaged magnetic potential and force for the guided atoms in the magneti c guiding tube are calculated. The results show that the potential is high enough to collect and guide nearly all cold atoms from a standard magneto-o ptical trap with a temperature of similar to 120 muK. We also estimate the atomic losses from collisions with background thermal atoms, quantum tunnel ing and spin-flip transitions in the guiding process. Our study indicates t hat a cold and dense atomic beam with a guiding efficiency of similar to 92 % and a beam intensity of about 10(11) atoms/cm(2)/s can be output from the magnetic guide tube, and the guiding scheme proposed here could be used to manipulate spin-polarized cold atoms. (C) 2001 Elsevier Science B.V. All r ights reserved.