Estimating Bounds on Collisional Relaxation Rates of Spin-Polarized87Rb Atoms at Ultracold Temperatures.
We present quantum scattering calculations for the collisional relaxation rate coefficient of spin-polarized87Rb(f= 2,m= 2) atoms, which determines the loss rate of cold Rb atoms from a magnetic trap. Unlike the lighter alkali atoms, spin-polarized87Rb atoms can undergo dipolar relaxation due to both the normal spin-spin dipole interaction and a second-order spin-orbit interaction with distant electronic states of the dimer. We presentab initiocalculations for the second-order spin-orbit terms for both Rb2and Cs2. The corrections lead to areductionin the relaxation rate for87Rb. Our primary concern is to analyze the sensitivity of the87Rb trap loss to the uncertainties in the ground state molecular potentials. Since the scattering length for thea3Σ+ustate is already known, the major uncertainties are associated with theX1Σ+gpotential. After testing the effect of systematically modifying the short-range form of the molecular potentials over a reasonable range, and introducing our best estimate of the second-order spin-orbit interaction, we estimate that in the low temperature limit the rate coefficient for loss of Rb atoms from thef= 2,m= 2 state is between 0.4 × 10-15cm3/s and 2.4 × 10-15cm3/s (where this number counts two atoms lost per collision). In a pure condensate the rate coefficient would be reduced by 1/2.
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
Frederick H
FH
Mies
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
Carl J
CJ
Williams
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
Paul S
PS
Julienne
National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
Morris
M
Krauss
ab initio calculations; cold trapped atoms; rubidium atom collisions; second-order spin-orbit; spin-relaxation rate; spin-spin interactions