Estimating bounds on collisional relaxation rates of spin-polarized 87Rb atoms at ultracold temperatures

The recent observation of Bose-Einstein condensation (BEC) in magnetically trapped alkali atoms has brought to completion a 15 year attempt to achieve BEC in a weakly interacting atomic system. The success of BEC in both 87Rb and 23Na and evidence for BEC in 7Li were remarkable achievements brought about by the development of laser cooling during the past decade, the design of optical and magnetic traps for holding cold atomic samples, and most recently the development of evaporative cooling techniques to cool atoms below the recoil limit. The authors present quantum scattering calculations for the collisional relaxation rate coefficient of spin-polarized 87Rb(f = 2, m = 2) atoms, which determines the loss rate of cold Rb atoms from a magnetic trap. Unlike the lighter alkali atoms, spin-polarized 87Rb atoms can undergo dipolar relaxation due to both the normal spin-spin dipole interaction and a second-order spin-orbit interaction with distance electronic states of the dimer. The authors present ab initio calculations for the second-order spin-orbit terms for both Rb2 and Cs2. The corrections lead to a reduction in the relaxation rate for 87Rb. The primary concern is to analyze the sensitivity of the 87Rb trap loss to the uncertainties in the ground state molecular potentials