Double-well Magnetic Traps For Neutral Atoms And Their Applications

Due to the Zeeman effect, the principle of magnetic trap for neutral atoms is based on the interaction potential between a neutral atom with a magnetic dipole moment and a static, inhomogeneous magnetic field. The atom in the strong (weak)-field-seeking state will be attractive (repulsed) to the trap center with the maximum (minimum) magnetic field when the interaction potential is negative (positive), which can be used to realize the three dimensional trap of cold atoms.In this thesis, we propose four novel controllable double-well magnetic traps (i.e., double loffe trap, double Z-shaped wire trap, double U-U-shaped wire trap and double U-Z-shaped wire trap) for cold neutral atoms using current-carrying wires (including current-carrying coils). We calculate the spatial distributions of the magnetic field, gradient and curvature generated by the above four trapping schemes and discussed their experimental feasibility to realize the double-well magnetic trap for cold atoms. Our study shows that the double-well traps proposed here can be used to realize the magnetic trap or magneto-optical trap (MOT) for two different atomic samples and can be continuously changed into a single-well trap by reducing the current in some wire, which can be used to experimentally study the collision mechanisms between two-species cold atoms and the interference between atomic matter waves, and so on. Further study finds that when the characteristic length of the trapping systems is equal to 200um and the currents in the wires are 0.2A, the magnetic-field gradients and curvatures of the double loffe trap and double Z-shaped wire trap at their well centers are typically 2.0 X103 G/cm and 1.0 X 105 G/cm2, which are far greater than those of macroscopic BEC magnetic traps. So our double-well magnetic microtraps can be used to realize a micro-well, two-species Bose-Einstein condensation (BEC).In the double loffe trap and double Z-shaped wire trap, the magnetic field at the well center is a nonzero minimum, there are no Majorana transitions, and a sufficient high atomic density can be obtained. Therefore these traps cannot only be used to study the collision mechanisms between two-species cold atoms, but also to realizetwo-species BEC and study the properties of two-species BEC. There are serious Majorana transitions because the magnetic fields of the double U-U-shaped wire trap and double U-Z-shaped wire trap at their well centers are equal to zero, which limits the increase of atomic density in the magnetic trap, so they can be only used to realize the two-species MOT and study the collision mechanisms between two-species cold atoms. Our study shows the magnetic gradients of the double U-U-shaped wire trapand double U-Z-shaped wire trap near their well centers are about 15 ~ 20G/cm when the currents in the wires are equal to 600A and the homogeneous bias magnetic field is equal to 40G. In this case, we can obtain two cold atomic samples with ~106 atoms in each MOT and a temperature of- 266 n K, which are similar to those in a standard MOT.