Anisotropic Hyperfine Interactions Limit the Efficiency of Spin-Exchange Optical Pumping of 3He Nuclei

We use accurate ab initio and quantum scattering calculations to demonstrate that the maximum He-3 spin polarization that can be achieved in spin-exchange collisions with potassium (K-39) and silver (Ag-107) atoms is limited by the anisotropic hyperfine interaction. We find that spin exchange in Ag-He collisions occurs much faster than in K-He collisions over a wide range of temperatures (10-600 K). Our analysis indicates that measurements of trap loss rates of S-2 atoms in the presence of cold He-3 gas may be used to probe anisotropic spin-dependent interactions in atom-He collisions.