  The inherent polarization gradients in tight optical tweezers can be used to
couple the atomic spins to the two-body motion under the action of a microwave
spin-flip transition, so that such a spin-motion coupling offers an important
control knob on the motional states of optically trapped two colliding atoms.
Here, after preparing two elastically scattering $^{85}$Rb atoms in the
three-dimensional ground-state in the optical tweezer, we employed this control
in order to probe the colliding energies of elastic and inelastic channels. The
combination of microwave spectra and corresponding s-wave pseudopotential model
allows us to infer the effect of the state-dependent trapping potentials on the
elastic colliding energies, as well as to reveal how the presence of inelastic
interactions affects elastic part of the relative potential. Our work shows
that the spin-motion coupling in a tight optical tweezer expand the
experimental toolbox for fundamental studies of ultracold collisions in the two
body systems with reactive collisions, and potentially for that of more complex
interactions, such as optically trapped atom-molecule and molecule-molecule
interactions.
