Loading and characterization of a printed-circuit-board atomic ion trap

We demonstrate loading of ${}^{88}\mathrm{Sr}^{+}$ ions into a $0.5\text{−}\mathrm{mm}$-scale printed circuit board surface-electrode ion trap. We then characterize the trap by measuring the secular frequencies and comparing them to a three-dimensional simulation of the trap, and by measuring the stray electric fields along two of the trap’s principal axes. Cancelling these fields by applying additional voltages enables a hundredfold increase in the trap lifetime to greater than ten minutes at a vacuum of ${10}^{-9}\text{torr}$.

Figure 1

(Color online) (a) Photograph showing the top electrode plate mounted $6.3\mathrm{mm}$ above the trap. The top plate has a slit for ion fluorescence detection. (b) Layout of trap electrodes, each labeled with the voltage applied; all but $V_{\mathrm{rf}}$ are dc. The space around the long electrodes ($V_{\mathrm{rf}}$ and $V_1$) has been milled out. Coordinates referenced as shown define the origin at the trap center and on the chip surface. (c) Charge-coupled device image of trapped strontium ions.

Figure 2

Cross sections of the pseudopotential along the $\widehat{x}$ and $\widehat{y}$ directions for $V_{\mathrm{rf}}=1260\mathrm{V}$ at $\Omega ∕2\pi =7.6\mathrm{MHz}$, $V_2=110\mathrm{V}$, and $V_3=-50\mathrm{V}$. The two figures (a) and (b) correspond to $V_{\text{top}}$ voltages of $-25.4$ and $15\mathrm{V}$, respectively. Micromotion compensation is expected in the $-25.4\mathrm{V}$ case, but with a depth of only $1\mathrm{eV}$, while the uncompensated $15\mathrm{V}$ case has an expected depth of $5.4\mathrm{eV}$. The position of the rf null is indicated in each plot by an “⊗.”

Figure 3

Calculated values of trap depth (hollow circles) and ion displacement from the rf null (solid diamonds) as $V_{\text{top}}$ is varied. As trap depth is increased, the displacement of the ion cloud from the rf null leads to increased micromotion.

Figure 4

Measurement results showing compensation of micromotion in the trap at a buffer gas pressure of $1\times {10}^{-5}\text{torr}$. (a) Cloud intensity profile along the $\widehat{y}$ axis, fit to a Gaussian, for a representative value of the $\widehat{y}$ compensation voltage, $V_{\text{top}}$. (b) Linear fit of the cloud center position versus $1∕{\omega }_1^2$, where ${\omega }_1$ is the secular frequency of the ion motion, yielding the electric field along $\widehat{y}$ at the rf node. (c) Plot of the $\widehat{y}$ electric field as a function of the $V_{\text{top}}$ compensating voltage, showing that the stray field is minimized at $V_{\text{top}}=1.0\mathrm{V}$. (d) Plot of the $\widehat{x}$ electric field as a function of the middle electrode voltage $V_5$, showing compensation at $V_5=1.3\mathrm{V}$.