A Linear AC Trap for Polar Molecules in Their Ground State

Abstract

A linear AC trap for polar molecules in high-field seeking states has been devised and implemented, and its characteristics have been investigated both experimentally and theoretically. The trap is loaded with slow 15 ND 3 molecules in their ground state (para-ammonia) from a Stark decelerator. The trap's geometry offers optimal access as well as improved loading. We present measurements of the dependence of the trap's performance on the switching frequency, which exhibit a characteristic structure due to nonlinear resonance effects. The molecules are found to oscillate in the trap under the influence of the trapping forces, which were analyzed using 3D numerical simulations. On the basis of expansion measurements, molecules with a velocity and a position spread of 2.1 m/s and 0.4 mm, respectively, are still accepted by the trap. This corresponds to a temperature of 2.0 mK. From numerical simulations, we find the phase-space volume that can be confined by the trap (the acceptance) to be 50 mm 3 (m/s) 3 .

ac electric trapping of neutral atoms

“…Similar trap depths were later obtained for the same molecule with a linear ac trap [12]. In the meantime, Katori and coworkers achieved trapping of about 100 ground-state Sr atoms with a lifetime of 80 ms in a microstructured ac trap on a chip [13].…”

Ultracold molecules and ultracold chemistry

“…Slowly moving molecules produced using this technique have already found many applications, including: high-resolution spectroscopy [14,18] and lifetime measurements [72,73]; trapping in static and AC electric fields [74][75][76][77][78]; magneto-electrostatic and magnetic trapping [79]; reflection from a microstructure or permanent magnet array [80,81] and tunable-energy collision studies [82]. More recently, a molecular synchrotron [83] has been constructed which confines molecules in bunches orbiting inside a split hexapole ring -a direct analogue of the charged-particle synchrotrons used for high-energy collision experiments.…”

“…The linear AC trap designed by Schnell et al [78], shown in Fig. 9(b), consisting of four 8 mm length double rods, has been used to capture 15 ND 3 molecules which were decelerated to 15 ms −1 before trapping.…”

“…Inelastic trap loss can be avoided, however, if the molecules are trapped in their ground state, which is possible using AC electric and magnetic fields [78,179,220] or an optical dipole trap formed in the focus of an intense off-resonant laser beam [185]. In the first step towards this goal, Schlunk and co-workers have demonstrated the successful transfer of magnetically trapped Rb atoms into an AC electric trap which could be used to confine Stark decelerated ammonia molecules [182,183].…”

Prospects for sympathetic cooling of molecules in electrostatic, ac and microwave traps

“…By alternating the focussing and defocussing directions at a suitable rate, molecules are confined near the trap centre. Such ac electric traps have already been used to trap polar molecules in strong-field-seeking states [41][42][43], and also to trap ground-state atoms [44,45], and sympathetic cooling of molecules in ac traps has been proposed [44,45].…”