Cort Johnson

Magnetic Trapping of Silver and Copper, and Anomalous Spin Relaxation in the Ag-He System

We have trapped large numbers of copper (Cu) and silver (Ag) atoms using buffer-gas cooling. Up to 3 x 10{12} Cu atoms and 4 x 10{13} Ag atoms are trapped. Lifetimes are as long as 5 s, limited by collisions with the buffer gas. Ratios of elastic to inelastic collision rates with He are >or=10{6}, suggesting Cu and Ag are favorable for use in ultracold applications. The temperature dependence of the Ag-3He collision rate varies as T;{5.8+/-0.4}. We find that this temperature dependence is inconsistent with the behavior predicted for relaxation arising from the spin-rotation interaction, and conclude that the Ag-3He system displays anomalous collisional behavior in the multiple-partial wave regime. Gold (Au) was ablated into 3He buffer gas, however, atomic Au lifetimes were observed to be too short to permit trapping.

Zeeman Relaxation of Cold Atomic Iron and Nickel in Collisions with \(^3\)He

We have measured the ratio γ of the diffusion cross section to the angular momentum reorientation cross section in the colliding Fe-(^3)He and Ni-(^3)He systems. Nickel (Ni) and iron (Fe) atoms are introduced via laser ablation into a cryogenically cooled experimental cell containing cold (<1 K) (^3)He buffer gas. Elastic collisions rapidly cool the translational temperature of the ablated atoms to the (^3)He temperature. γ is extracted by measuring the decays of the atomic Zeeman sublevels. For our experimental conditions, thermal energy is comparable to the Zeeman splitting. As a result, thermal excitations between Zeeman sublevels significantly impact the observed decay. To determine γ accurately, we introduce a model of Zeeman state dynamics that includes thermal excitations. We find γ(_{Ni-^{3}He}=5×10^3) and γ(_{Fe-^{3}He}leq3×10^3) at 0.75 K in a 0.8 T magnetic field. These measurements are interpreted in the context of submerged shell suppression of spin relaxation, as studied previously in transition metals and rare earth atoms.