The Stark interaction of polar molecules with an inhomogeneous electric field is exploited to select slow molecules from a room-temperature reservoir and guide them into an ultrahigh vacuum chamber. A linear electrostatic quadrupole with a curved section selects molecules with small transverse and longitudinal velocities. The source is tested with formaldehyde (H 2 CO) and deuterated ammonia (ND 3 ). With H 2 CO a continuous flux is measured of Ϸ10 9 /s and a longitudinal temperature of a few kelvin. The data are compared with the result of a Monte Carlo simulation.The past years have seen an explosion of activity in the field of cold atomic gases ͓1͔. It is interesting and desirable to extend these investigations to molecules, which have a complex internal structure and can as a consequence possess a permanent electric dipole moment. Trapping cold polar molecules will lead to new physics due to the long range and anisotropy of the dipole-dipole interaction ͓2͔. Slow molecules for precision measurements or interferometry are further motivations behind the ongoing efforts. However, the complexity and density of energy levels in the rotational and vibrational manifolds largely precludes the effective use of laser cooling techniques ͓3͔. Therefore, a number of different approaches have been considered for cooling and trapping molecules. Buffer-gas cooling in a cryogenic environment is one possibility, but requires a rather complex setup ͓4͔. Another method is photoassociation, but this is limited to simple molecules with laser-cooled precursor atoms ͓5͔. A different technique uses deceleration by the Stark effect, where packages of polar molecules are decelerated with time-varying electric fields ͓6-8͔. Other, mostly mechanical methods have also been proposed but remain to be demonstrated ͓9,10͔.It is, however, not necessary to produce slow molecules, as they are present in any thermal gas, even at room temperature. Slow molecules only need to be filtered out. For this reason, already in the 1950s it was attempted to select the slowest atoms from a hot beam using gravity ͓11͔. These attempts failed, mostly because the slow particles were kicked away by the fast ones. Much later, it was demonstrated that slow lithium atoms can be efficiently guided out of a hot beam with strong permanent magnets, providing a robust and cheap source of slow atoms ͓12͔, e.g., for Bose-Einstein condensation experiments. In the same spirit, an efficient and simple filtering technique could play an important role towards the production of a cold molecular gas.In this paper we describe an experiment in which the Stark interaction of polar molecules with an inhomogeneous, electrostatic field is exploited to efficiently select and guide slow molecules out of a room-temperature reservoir into ultrahigh vacuum. Whether a dipolar molecule is weak-field seeking and trapped by an electric-field minimum, or strongfield seeking and expelled, depends on whether the average orientation of the rotating molecular dipole is antiparallel or parallel to t...

In mixed systems of trapped ions and cold atoms, the ions and atoms can coexist at different temperatures. This is primarily due to their different trapping and cooling mechanisms. The key questions of how ions can cool collisionally with cold atoms and whether the combined system allows stable coexistence, need to be answered. Here we experimentally demonstrate that rubidium ions cool in contact with magneto-optically trapped rubidium atoms, contrary to the general experimental expectation of ion heating. The cooling process is explained theoretically and substantiated with numerical simulations, which include resonant charge exchange collisions. The mechanism of single collision swap cooling of ions with atoms is discussed. Finally, it is experimentally and numerically demonstrated that the combined ion-atom system is intrinsically stable, which is critical for future cold chemistry experiments with such systems.

We measure the collision rate coefficient between laser cooled Rubidium (Rb) atoms in a magnetooptical trap (MOT) and optically dark Rb + ions in an overlapping Paul trap. In such a mixture, the ions are created from the MOT atoms and allowed to accumulate in the ion trap, which results in a significant reduction in the number of steady state MOT atoms. A theoretical rate equation model is developed to describe the evolution of the MOT atom number, due to ionization and ion-atom collision, and derive an expression for the ion-atom collision rate coefficient. The loss of MOT atoms is studied systematically, by sequentially switching on the various mechanisms in the experiment. Combining the measurements with the model allows the direct determination of the ion-atom collision rate coefficient. Finally the scope of the experimental technique developed here is discussed.

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A continuously operated electrostatic trap for polar molecules is demonstrated. The trap has a volume of approximately 0.6 cm3 and holds molecules with a positive Stark shift. With deuterated ammonia from a quadrupole velocity filter, a trap density of approximately 10(8) cm(-3) is achieved with an average lifetime of 130 ms and a motional temperature of approximately 300 mK. The trap offers good starting conditions for high-precision measurements, and can be used as a first stage in cooling schemes for molecules and as a "reaction vessel" in cold chemistry.