Two-Dimensional Trapping of Dipolar Molecules in Time-Varying Electric Fields

Abstract

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...

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