Timothy Roach

We have studied the interaction of cold atoms with ferromagnetic surfaces. The atomic source is a magneto-optic trap (MOT) that captures Rb atoms from a dilute vapor and cools them to 30 $\mu$K in a 1 mm diameter cloud. In our experiments we place a magnetic sample 2-4 cm below the trap and release the atoms, allowing them to fall and hit the surface. Due to the interaction between the atomic magnetic dipole and the locally strong surface field, atoms in weak-field-seeking states are repelled from the surface (Stern-Gerlach effect). We observe these rebounding atoms by recapturing them in the MOT. We have used a variety of magnetic surfaces including audiotape, floppy disks and thin iron films. The surfaces were prepared either with a spatially periodic or a random magnetization pattern and on both flat and concave surfaces. We find that the atomic reflectivity for both periodic and randomly magnetized surfaces is high but the former is specularly reflecting while the latter is diffusely reflecting, which we show is in agreement with theoretical expectations. We measure the reflectivity for a periodically magnetized surface to be at least (89 $\pm$ 8) %. We demonstrate that a concave periodically magnetized surface confines the atoms horizontally (i.e., focuses them) and we observe up to 8 bounces of an atomic cloud confined in this manner for 1 second. We conclude that these surfaces show great promise for the storage and manipulation of cold atoms.