Radio-frequency ac Zeeman force for ultracold atoms

We measure the ac Zeeman force acting on ultracold $^{87}\mathrm{Rb}$ atoms due to a radio frequency (rf) field driving intramanifold Zeeman transitions near 8 MHz. We observe about 2.5 times the force of gravity for $\ensuremath{\approx}14$ mW of rf power acting on atoms $\ensuremath{\approx}100\phantom{\rule{4pt}{0ex}}\textmu{}\mathrm{m}$ from the atom chip. Our measurements are consistent with theoretical predictions and demonstrate the spin-state dependence of the force, as well as its resonant and bipolar behavior. We demonstrate the ac Stern-Gerlach effect by spatially separating a spin mixture, using initial detuning to determine which spins are ac Zeeman high- and low-field seekers. With an eye towards using this force for atom trapping, we observe the time dependence of dressed state spin mixing as a function of detuning and power.