Trapping Molecules on a Chip in Traveling Potential Wells

A microstructured array of over 1200 electrodes on a substrate has been configured to generate an array of local minima of electric field strength with a periodicity of $120\mu \mathrm{m}$ about $25\mu \mathrm{m}$ above the substrate. By applying sinusoidally varying potentials to the electrodes, these minima can be made to move smoothly along the array. Polar molecules in low field seeking quantum states can be trapped in these traveling potential wells. This is experimentally demonstrated by transporting metastable CO molecules in 30 mK deep wells that move at constant velocities above the substrate.

Figure 1

(a)–(c): Contour lines of equal electric field strength in a plane perpendicular to both the substrate and the electrodes, shown in $0.2\mathrm{kV}/\mathrm{cm}$ intervals, for three different times in the rf cycles. The instantaneous potentials applied to the $10\mu \mathrm{m}$ wide electrodes are indicated (in volts). The dashed horizontal lines are at the same height above the substrate in (a)–(c). The electric field strength (solid black curve) and the Stark shift for metastable CO molecules (dashed red curve) are shown around the minima as a function of position along the $z$ axis (d) and as a function of height above the substrate (e). Note that the right vertical axes have an offset.

Figure 2

Upper part: Scheme of the microstructured electrode array at different levels of detail. The applied waveforms are schematically indicated. Lower part: Scheme of the experimental setup. A pulsed laser prepares the metastable CO molecules in the desired quantum state. After passing through a skimmer and a narrow slit the molecules travel closely above the microstructured electrode array, over its full 5.0 cm length, and then pass through a second narrow slit. Time-resolved detection of the metastable CO molecules takes place another 6 cm further downstream. In the lower right corner, the arrival time distribution of the metastable CO molecules is shown when no voltages are applied to the electrodes.

Figure 3

Arrival time distributions of metastable CO molecules, for seven different frequencies $\omega /2\pi$, corresponding to velocities of the traveling potential wells ranging from $276$ to $348\mathrm{m}/\mathrm{s}$. The enveloping curve is the arrival time distribution of the molecules in free flight, scaled down for this comparison.