Electrostatic trapping of ammonia molecules

The ability to cool and slow atoms with light for subsequent trapping(1-3) allows investigations of the properties and interactions of the trapped ato ms in unprecedented detail. By contrast, the complex structure of molecules prohibits this type of manipulation, but magnetic trapping of calcium hydr ide molecules thermalized in ultra-cold buffer gas(4) and optical trapping of caesium dimers(5) generated from ultra-cold caesium atoms have been repo rted. However, these methods depend on the target molecules being paramagne tic or able to form through the association of atoms amenable to laser cool ing(6-8), respectively, thus restricting the range of species that can be s tudied. Here we describe the slowing of an adiabatically cooled beam of deu terated ammonia molecules by time-varying inhomogeneous electric fields(9,1 0) and subsequent loading into an electrostatic trap. We are able to trap s tate-selected ammonia molecules with a density of 10(6) cm(-3) in a volume of 0.25 cm(3) at temperatures below 0.35 K. We observe pronounced density o scillations caused by the rapid switching of the electric fields during loa ding of the trap. Our findings illustrate that polar molecules can be effic iently cooled and trapped, thus providing an opportunity to study collision s and collective quantum effects in a wide range of ultra-cold molecular sy stems(11-14).