MAGNETIC TRAPPING OF CALCIUM MONOHYDRIDE MOLECULES AT MILLIKELVIN TEMPERATURES

Recent advances(1-5) in the magnetic trapping and evaporative cooling of atoms to nanokelvin temperatures have opened important areas of res earch, such as Bose-Einstein condensation and ultracold atomic collisi ons. Similarly, the ability to trap and cool molecules should facilita te the study of ultracold molecular physics and collisions(6); improve ments in molecular spectroscopy could be anticipated. Also, ultracold molecules could aid the search for electric dipole moments of elementa ry particles(7). But although laser cooling (in the case of alkali met als(1,8,9)) and cryogenic surface thermalization (in the case of hydro gen(10,11)) are currently used to cool some atoms sufficiently to perm it their loading into magnetic trays, such techniques are not applicab le to molecules, because of the latter's complex internal energy-level structure. (Indeed, most atoms have resisted trapping by these techni ques.) We have reported a more general loading technique(12) based on elastic collisions with a cold buffer gas, and have used it to trap at omic chromium and europium(13,14). Here we apply this technique to mag netically trap a molecular species-calcium monohydride (CaH). We use Z eeman spectroscopy to determine the number of trapped molecules and th eir temperature, and set upper bounds on the cross-sectional areas of collisional relaxation processes. The technique should he applicable t o many paramagnetic molecules and atoms.