ac electric trap for ground-state molecules

We here report on the realization of an electrodynamic trap, capable of trapping neutral atoms and molecules in both low-field and high-field seeking states. Confinement in three dimensions is achieved by switching between two electric field configurations that have a saddle point at the center of the trap, i.e., by alternating a focusing and a defocusing force in each direction. The ac trapping of (ND3)-N-15 molecules is experimentally demonstrated, and the stability of the trap is studied as a function of the switching frequency. A 1 mK sample of (ND3)-N-15 molecules in the high-field seeking component of the {\J,K>=\1,1>} level, the ground state of para-ammonia, is trapped in a volume of about 1 mm(3).