A molecular synchrotron

Abstract

Many of the tools for manipulating the motion of neutral atoms and molecules take their inspiration from techniques developed for charged particles. Traps for atoms—akin to the Paul trap for ions—have paved the way for many exciting experiments, ranging from ultra-precise clocks to creating quantum degenerate matter. Surprisingly, little attention has been paid to developing a neutral particle analogue of a synchrotron—arguably, the most celebrated tool of the charged-particle physicist. So far, the few experiments dealing with ring structures for neutral particles have used cylindrically symmetric designs; in these rings, no force is applied to the particles along the longitudinal direction and the stored particles are free to fill the entire ring. Here, we demonstrate a synchrotron for neutral polar molecules. A packet of ammonia molecules is accelerated, decelerated and focused along the longitudinal direction ('bunched') using the fringe fields between the two halves of a segmented hexapole ring. The stored bunch of cold molecules (T=0.5 mK) is confined to a 3 mm packet even after a flight distance of over 30 m (40 round trips). Furthermore, we show the injection of multiple packets into the ring

A Forty-Segment Molecular Synchrotron

“…After the successful implementation of this first storage ring, C. E. Heiner and coworkers demonstrated a sectioned storage ring consisting of two hexapoles bent into a semicircle with a radius of 125 mm, separated by a 2 mm gap [24]. By switching the electric field synchronously with the motion of the molecules, the electric fields in the gap are used to keep the molecular packet confined in the longitudinal direction.…”

“…The top right panel shows the second generation molecular storage ring: the prototype molecular synchrotron, consisting of two hexapole bent into a semi circle, separated by 2 mm wide gaps. The measurement under the ring shows the ND 3 intensity as a function of storage time (reproduced from [24]). Here, due to the applied switching scheme, the molecular packet is confined as a tight bunch in an effective three dimensional potential well.…”

Cold SO2 molecules by Stark deceleration

“…Here, molecules were decelerated from 285 m/s to 53 m/s. This final velocity is very close to typical velocities that are used to load electrostatic traps [3,30,31]. A slight increase of the phase angle would have been sufficient to achieve this but the detection of the particles would have been very difficult due to dispersion of the bunches during the time-of-flight from the end of the decelerator to the interaction zone.…”

“…For these molecules Stark deceleration has proved to be a very efficient method to generate cold samples [1,2]. The decelerated molecules can be confined for long times [3,4] and can be used for collision studies with precise control over the translational degrees of freedom [5].…”

Experiments with Stark decelerated and trapped OH radicals

“…In our group, this has been explicitly demonstrated by the construction of various types of decelerators [8,11], a buncher [12], various types of traps [2,13], and a storage ring for neutral polar molecules [14]. Recently, also a molecular synchrotron has been experimentally realized [15] [20]. Of these, the molecules ND 3 [2], OH [3] and OD [17] have been trapped.…”