A Cryogenic Trap for Neutral Atoms

A cryogenic system for the trapping and cooling of neutral atoms is described. The system uses superconducting coils inside a trapping chamber cooled to liquid helium temperatures. The cryogenic nature of the system allows the production of extremely long-lived traps at high field gradients and curvatures. At the highest field gradients, evidence for discrete jumps in the trap fluorescence is presented; these jumps are shown to be due to single atoms entering and leaving the trap. The stability of high field gradient traps is studied, and a newly identified loss mechanism, stochastic diffusion, is shown to be the dominant loss mechanism for such traps. Finally, evidence for evaporative cooling of cesium is presented, and an upper bound to a cross section critical to the evaporation process is obtained.