Trapping of Neutral Rubidium with a Macroscopic Three-Phase Electric Trap

We trap neutral ground-state rubidium atoms in a macroscopic trap based on purely electric fields. For this, three electrostatic field configurations are alternated in a periodic manner. The rubidium is precooled in a magneto-optical trap, transferred into a magnetic trap, and then translated into the electric trap. The electric trap consists of six rod-shaped electrodes in cubic arrangement, giving ample optical access. Up to ${10}^5\mathrm{\text{atoms}}$ have been trapped with an initial temperature of around 20 microkelvin in the three-phase electric trap. The observations are in good agreement with detailed numerical simulations.

Figure 1

The ac electric trap. (a) The 6 electrodes. (b) The switching diagram, indicating that in each full cycle each pair of electrodes is switched on for one third of the time. (c)–(e) The absolute value of the electric field in the $x\mathrm{\text{−}}y$ plane in the three consecutive phases of a full driving cycle with electrodes at $\pm 7\mathrm{kV}$.

Figure 2

The frequency dependence of the trapped number of atoms after 50 ms for electrodes at $\pm 7\mathrm{kV}$. The square symbols are data; the triangles are the result of a Monte Carlo simulation. Noise in the background images can lead to negative values. The simulation result is scaled to fit the height of the data. The inset shows the measured dependence of the frequency of the maximum $f_{\mathrm{peak}}$ as a function of the electrode voltage. The expected linear dependence is indicated by the line.

Figure 3

Remaining number of atoms as a function of time. At $t=0$ the magnetic trap contains $2.7\times {10}^6\mathrm{\text{atoms}}$. The initial rapid decay is caused by atoms which enter the electric trap on nontrapped orbits, either because they are too hot or because their motion has the wrong phase. The decay of the trapped atoms, visible as the long tail with a $1/e$ time of 0.36 s, is attributed to collisions with background gas. The inset shows, for another set of data with other starting conditions, the dependence of the maximum number of trapped atoms after 50 ms electric trapping as a function of the applied voltage. The line is a guide to the eye.

Figure 4

(a) Measured and (b) simulated camera pictures of the trapped cloud at the times indicated 1, 2, 3, 4 in (c). Each picture in (a) is an average over 10 measurements. The 19.5° tilt with respect to the vertical corresponds to the tilt angle of the trap mounting. (c) Measured (squares) and simulated (triangles) aspect ratio of the elliptic clouds. The boxes with letters $x$, $y$, $z$, $x$ indicate the charged electrodes. Note that the simulation has no free parameters.