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...

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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.

Simultaneous two-dimensional trapping of neutral dipolar molecules in low-and high-field seeking states is analyzed. A trapping potential of the order of 20 mK can be produced for molecules like ND3 with time-dependent electric fields. The analysis is in agreement with an experiment where slow molecules with longitudinal velocities of the order of 20 m/s are guided between four 50 cm long rods driven by an alternating electric potential at a frequency of a few kHz.PACS numbers: 33.80. Ps, 33.55.Be, 39.10.+j Cold molecules offer new perspectives, e.g. for high precision measurements [1] and collisional physics studies [2]. Pioneering work on cold molecules has been done using cryogenic buffer gas cooling [3]. Another promising technique for the production of cold molecules is based on the interaction of dipolar molecules with inhomogeneous electric fields. For example, low-field seeking molecules (LFS) have been slowed down in suitably tailored timevarying electric fields [4] and have been trapped in inhomogeneous electrostatic fields [5,6]. Furthermore, efficient filtering [7] of slow LFS from an effusive thermal source using a bent electrostatic quadrupole guide has been demonstrated [8].Compared to LFS, the manipulation of high-field seeking molecules (HFS) is much more difficult. This is mainly due to the fact that electrostatic maxima are not allowed in free space, and hence, HFS are quickly lost on the electrodes. Nevertheless, guiding of HFS in Keppler orbits [9] and deceleration as well as acceleration of HFS [10] is possible. Despite this progress in manipulating dipolar molecules, all techniques realized so far are suited only for either LFS or HFS, not both simultaneously. However, in future experiments with trapped samples of cold molecules, collisions or the interaction with light fields are likely to change HFS into LFS and vice versa. Therefore, a technique to trap both species simultaneously is vital. In this Letter, we investigate both theoretically and experimentally a new technique, which can trap both HFS and LFS. In particular, we report on the first experimental demonstration of two-dimensional trapping of slow ND 3 molecules from an effusive source in a bent four-wire guide driven by an alternating electric field.Trapping neutral particles in oscillating electric fields works as follows [11]. The force on a molecule in an electric field, E, is given by F = − ∇W (E), with W (E) the Stark energy of the molecule. Polar molecules like ND 3 and H 2 CO predominantly experience a linear Stark shift, W = s E, where s is the slope of the Stark shift. Other molecules, however, and atoms usually experience a quadratic Stark effect, W = − rapidly switched between two dipole-like configurations with angular frequency ω. Close to the center, the field can be expanded harmonically,where E 0 is the field in the center and β is (half) the curvature of the field. The step function H(t) = 1 if nT < t < (n + 1 2 )T and H(t) = −1 otherwise, with T = 2π/ω the period of the driving field and n an integer.Indep...

We report the creation of a confined slow beam of heavy-water (D2O) molecules with a translational temperature around 1 kelvin. This is achieved by filtering slow D2O from a thermal ensemble with inhomogeneous static electric fields exploiting the quadratic Stark shift of D2O. All previous demonstrations of electric field manipulation of cold dipolar molecules rely on a predominantly linear Stark shift. Further, on the basis of elementary molecular properties and our filtering technique we argue that our D2O beam contains molecules in only a few ro-vibrational states. Cold dilute molecular systems are rapidly emerging as a front line area at the interface of quantum optics and condensed matter physics [1]. An increasing subset of this activity centers around the creation of cold dilute gases of molecules possessing electric dipole moments. These in particular, owing to their long-range anisotropic interaction, hold the promise of novel physics, where twoand many-body quantum properties can be systematically studied. Cold dilute gases of dipolar molecules can be produced by forging a tight bond between two chemically distinct species of laser-cooled atoms, e.g. RbCs [2]. Alternatively, cold dilute gas ensembles can be created by buffer-gas loading [3] Here we report the creation of a slow beam of heavywater (D 2 O) molecules, which experience a quadratic Stark effect. The cold D 2 O molecules are filtered from a room-temperature thermal gas [6] and have a translational temperature around 1 kelvin. Because the Stark shifts are quadratic in the electric field, it follows that forces exerted by inhomogeneous electric fields are relatively small for D 2 O compared to molecules with similar dipole moments but with linear Stark shifts. It is therefore by no means obvious that significant quantities of slow D 2 O molecules can be produced by means of electric-field-based methods. Our experimental result therefore underlines the versatility of the velocityfiltering method. It is an enabling step towards future trapping of molecules for which the ratio of elastic to inelastic collisions is expected to be more favorable than for molecules with linear Stark shifts [11]. An additional advantage of the quadratically Stark-shifted molecules like D 2 O is the possibility to perform precise spectroscopic measurements insensitive to stray electric fields, to the first order. Moreover, water is abundant in interstellar space at low densities and temperatures from a few kelvin upward, playing an important role in the chemistry of molecular clouds [12]. The conditions in these clouds are remarkably close to those achieved in our experiment, opening up the possibility to investigate in the laboratory chemical reactions under conditions found in space.This Letter is structured as follows. First we discuss general features of Stark shifts of molecular states with particular references to D 2 O. We then present our experimental work with D 2 O. This is followed by arguing from first principles that the resulting beam of D 2 O is domina...