Person:

Sadeghpour, Hossein

We predict that a large class of helium-containing cold polar molecules form readily in a cryogenic buffer gas, achieving densities as high as 10(^{12})  cm(^{-3}). We explore the spin relaxation of these molecules in buffer-gas-loaded magnetic traps and identify a loss mechanism based on Landau-Zener transitions arising from the anisotropic hyperfine interaction. Our results show that the recently observed strong (T^{-6}) thermal dependence of the spin-change rate of silver (Ag) trapped in dense (^{3})He is accounted for by the formation and spin change of Ag(^{3})He van der Waals molecules, thus providing indirect evidence for molecular formation in a buffer-gas trap.

We present a joint experimental and theoretical study of spin depolarization in collisions of alkali-metal atoms with (^3)He in a magnetic field. A rigorous quantum theory for spin-changing transitions is developed and applied to calculate the spin exchange and spin relaxation rates of Li and K atoms in cryogenic (^3)He gas. Magnetic trapping experiments provide upper bounds to the spin exchange rates for Li-(^3)He and K-(^3)He, which are in agreement with the present theory. Our calculations demonstrate that the alkali-metal atoms have extremely slow spin depolarization rates, suggesting a number of potential applications in precision spectroscopy and quantum optics.