We have measured the elastic-scattering cross section of
87Rb atoms in the \ensuremath{\Vert}F=1,
mF=-1〉 ground state at 25 \ensuremath{\mu}K. The cross section is almost purely s wave at these temperatures and has a value of (5.4\ifmmode\pm\else\textpm\fi{}1.3)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}12}$
cm2. We have searched for the predicted Feshbach-type resonances in the elastic cross section [Tiesinga et al., Phys. Rev. A 46, 1167 (1992)] as a function of magnetic field. There are no resonances with a magnetic-field width \ensuremath{\ge}2 G over a magnetic-field range of 15--540 G.
Abstract Optical tweezers are used to facilitate cold collisions between two Rydberg rubidium atoms (87Rb) by controlling the impact parameter and collision energy. One atom is held stationary while the other is propelled to a constant velocity. After the tweezers are deactivated, both atoms are excited to a Rydberg state using a π-pulse. Following the collision, a second π-pulse is applied. If the stationary atom undergoes minimal momentum transfer and returns to its ground state, it can be recaptured when the tweezer is reactivated. The collision probability as a function of the impact parameter is extracted from the atom loss in the tweezer and used to determine the collisional cross section between Rydberg atoms. Numerical simulations of elastic two-body collisions agree well with the experimental data, providing valuable insights into the parameter regime where quantum effects will become important.
We have measured the time taken for a magnetically trapped cloud of cold cesium atoms in the ${(F=3,m}_{F}=\ensuremath{-}3)$ ground state to rethermalize from a nonequilibrium spatial and velocity distribution. From these measurements we infer the dependences of the elastic scattering cross section on temperature and magnetic field in the ranges $1\ensuremath{-}30\ensuremath{\mu}\mathrm{K}$ and 0.05--2.0 mT, respectively. We determine a lower bound on the magnitude of the $(3,\ensuremath{-}3)+(3,\ensuremath{-}3)$ s-wave scattering length of
940a0.