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

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 such as ${\mathrm{ND}}_3$ with time-dependent electric fields. The analysis is in agreement with an experiment where slow molecules with longitudinal velocities of the order of $20\mathrm{m}/\mathrm{s}$ are guided between four 50 cm long rods driven by an alternating electric potential at a frequency of a few kHz.

Figure 1

Schematic of the four-wire setup for typical operating voltages of $\pm 5\mathrm{kV}$, where $E_0=35\mathrm{kV}/\mathrm{cm}$ and $\beta =2.3\times {10}^3\mathrm{kV}/{\mathrm{cm}}^3$. The voltages on a pair of opposite electrodes are switched, as shown in (a), in order to produce a time-varying field that alternates between configurations 1 and 2, shown in (b), with a repetition rate in the kHz range. The radius $r_{\max }$ used in simulations is indicated by the dashed circles.

Figure 2

Area of guided molecules in transverse-velocity space obtained from a two-dimensional Monte-Carlo simulation. Curves for LFS [down-pointing black and grey (red) triangles] and HFS [up-pointing black and grey (red) triangles] ${\mathrm{ND}}_3$ molecules with the given Stark shifts are displayed.

Figure 3

Schematic of the experimental setup. ${\mathrm{ND}}_3$ molecules emerging from the nozzle are injected into the guide. The slowest molecules are kept within the guide, and after passing two differential pumping stages, they enter a UHV chamber where they are detected with a mass spectrometer. The fast molecules are pumped away.

Figure 4

(a) Molecular flux as a function of the applied frequency for rod voltages of $\pm 5\mathrm{kV}$. The graph in the inset shows the frequency of maximum flux, ${\omega }_0$, as a function of the applied voltage. The dashed line indicates the ${\omega }_0\propto \sqrt{V}$ dependence. (b) Flux as a function of the applied voltage. For each voltage, the frequency is adjusted for maximum flux according to (a). The line is a quadratic fit.