We design and build a new experimental setup to demonstrate a mixture of a single nanoparticle and laser-cooled atoms. This system aims for investigating the low-energy scattering of ultracold atoms by a dielectric nanoparticle. The wave nature of the cold atoms manifests itself in both elastic and inelastic cross sections. In the new experimental system at Yokohama National University, we demonstrated optical trapping and cooling of a glass nanoparticle in vacuum. The ballistic Brownian motion of the nanoparticle in the harmonic potential was observed. We also demonstrated parametric cooling of the center of mass motion of the nanoparticle. We discuss the prospects for realization of a mixture of a single nanoparticle and laser-cooled atoms.
Ultracold atom experiments use a gas of neutral atoms with temperatures less than 100 µK above absolute zero and offer unmatched experimental control of quantum states and coherence, which has allowed ultracold atom-based measurements to be some of the most precise to date. While ultracold atom experiments can control almost all atomic degrees of freedom, spin-dependent trapping and spatial manipulation has remained difficult if not inaccessible. We are developing a method of spin-dependent trapping and spatial manipulation for ultracold neutral atoms using the AC Zeeman force produced by a microwave magnetic near-field gradient generated by an atom chip. We measure the AC Zeeman force on ultracold rubidium atoms by observing its effect on the motion of atoms in free-fall and on those confined in a trap. We have studied the force as a function of microwave frequency detuning from a hyperfine transition at 6.8 GHz at several magnetic field strengths and have observed its characteristic bipolar and resonant features predicted by two-level dressed atom theory. We find that the force is several times the strength of gravity in our setup, and that it can be targeted to a specific hyperfine transition while leaving other hyperfine states and transitions relatively unaffected. We find that our measurements are reasonably consistent with parameter-free theoretical predictions.