Stability of a superconductive atom chip with persistent current

The lifetime of Rb-87 atoms trapped in a z wire trap generated by a closed-circuit superconductive current on a MgB2 strip is measured as a function of the distance between the atom and the strip. The lifetime is found to be longer than 10 s at a distance of 40 mu m. This value is an order of magnitude longer than the lifetime of a trap generated by a normal current at the same distance. However, it is many orders of magnitude shorter than the theoretical decay rate induced by the spin-flip transition caused by the fluctuation of the current. This shows that for a type-II superconductor the dominant trap loss mechanism is not the spin-flip transition caused by noise as with a normal current atom trap. An analysis of our measurement suggests that magnetic field distortion resulting from flux penetration into the superconductor leads to much faster decay.